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C KC Kwww.GOALias.blogspot.comwww.GOALias.blogspot.comwww.GOALias.blogspot.comChapterwww.GOALias.blogspot.comChapterwww.GOALias.blogspot.comLightwww.GOALias.blogspot.comWaterwww.GOALias.blogspot.comhapter 13Motionand Time143hapter 14ElectricCurrentand its Effects160Chapter15ight 174Chapter16ater: : A PreciousResource193Chapter17Forestsorests: : OurLifeline206www.GOALias.blogspot.comChapterhapter 18WastewaterStory220www.GOALias.blogspot.comINDEXINDEX 231www.GOALias.blogspot.comwww.GOALias.blogspot.comwww.GOALias.blogspot.comwww.GOALias.blogspot.comwww.GOALias.blogspot.comwww.GOALias.blogspot.comwww.GOALias.blogspot.comxiv

www.GOALias.blogspot.com1Nutrition in PlantsIn Class VI you learnt that food isessential for all living organisms.You also learnt that carbohydrates,proteins, fats, vitamins and minerals arecomponents of food. These componentsof food are necessary for our body andare called nutrients.All living organisms require food.Plants can make their food themselvesbut animals including humans cannot.They get it from plants or animals thateat plants. Thus, humans and animalsare directly or indirectly dependent onplants.1.1 MBoojho wants to knowhow plants preparetheir own food.1.1 MODEOF NUTRITIONIN PLANTSPlants are the only organisms that canprepare food for themselves by usingwater, carbon dioxide and minerals. Theraw materials are present in theirsurroundings.The nutrients enable livingorganisms to build their bodies, to grow,to repair damaged parts of their bodiesand provide the energy to carry out lifeprocesses. Nutrition is the mode oftaking food by an organism and itsutilisation by the body. The mode ofnutrition in which organisms make foodthemselves from simple substances iscalled autotrophic (auto = self; trophos= nourishment) nutrition. Therefore,plants are called autotrophs. Animalsand most other organisms take in readymade food prepared by the plants. Theyare called heterotrophs (heteros =other).Now we may ask where the foodfactories of plants are located: whetherfood is made in all parts of a plant oronly in certain parts? How do plantsobtain the raw materials from thesurroundings? How do they transportthem to the food factories of the plants?1.2.2Paheli wants to know whyour body cannot make foodfrom carbon dioxide, waterand minerals like plants do..2 PHOTOSYNTHESIS— FOODMAKINGPROCESSIN PLANTSLeaves are the food factories of plants.The synthesis of food in plants occursin leaves. Therefore, all the rawmaterials must reach there. Water andminerals present in the soil are absorbedby the roots and transported to the

www.GOALias.blogspot.comCellsYou have seen that buildings are made of bricks.Similarly, the bodies of living organisms aremade of tiny units called cells. Cells can be seenonly under the microscope. Some organismsare made of only one cell. The cell is enclosed bya thin outer boundary, called the cell membrane.Most cells have a distinct, centrally locatedspherical structure called the nucleus (Fig. 1.1).The nucleus is surrounded by a jelly-likesubstance called cytoplasm.NucleusCytoplasmCell membraneFig. 1.1 Cellleaves. Carbon dioxide from air is takenin through the tiny pores present on thesurface of the leaves. These pores aresurrounded by ‘guard cells’. Such poresare called stomata [Fig. 1.2 (c)].Boojho wants to know how waterand minerals absorbed by rootsreach the leaves.Water and minerals are transportedto the leaves by the vessels which runlike pipes throughout the root, the stem,the branches and the leaves. They forma continuous path or passage for thenutrients to reach the leaf. You will learnabout transport of materials in plantsin Chapter 11.Paheli wants to know what is sospecial about the leaves that theycan synthesise food but otherparts of the plant cannot.The leaves have a green pigmentcalled chlorophyll. It helps leaves tocapture the energy of the sunlight. Thisenergy is used to synthesise (prepare)food from carbon dioxide and water.Since the synthesis of food occurs in thepresence of sunlight, it is calledphotosynthesis (Photo: light; synthesis :to combine). So we find that chlorophyll,sunlight, carbon dioxide and water arenecessary to carry out the process ofphotosynthesis. It is a unique processon the earth. The solar energy iscaptured by the leaves and stored in theplant in the form of food. Thus, sun isthe ultimate source of energy for allliving organisms.Can you imagine the earth in theabsence of photosynthesis!In the absence of photosynthesisthere would not be any plants. Thesurvival of almost all living organismsdirectly or indirectly depends upon thefood made by the plants. Besides,oxygen which is essential for the survival2SCIENCE

www.GOALias.blogspot.comBesides leaves, photosynthesis also takes place in other green parts of theplant — in green stems and green branches. The desert plants have scale- orspine-like leaves to reduce loss of water by transpiration. These plants havegreen stems which carry out photosynthesis.of all living organisms is producedduring photosynthesis. In the absenceof photosynthesis, life would beimpossible on the earth.During photosynthesis, chlorophyllcontaining cells of leaves (Fig. 1.2), inthe presence of sunlight, use carbondioxide and water to synthesisecarbohydrates (Fig. 1.3). The processcan be represented as an equation:Carbon dioxideCarbohydratewateroxygenChlorophyllsunlightchlorophyllCarbondioxideOxygenLight energyChlorophyllin leafFig. 1.3 Schematic diagram showingphotosynthesisWater andmineralsDuring the process oxygen isreleased. The carbohydrates ultimatelyget converted into starch. The presenceof starch in leaves indicates theoccurrence of photosynthesis. Thestarch is also a carbohydrate.(a) LeafGuard cell Stoma(b) A section through a leafGuard cellsBoojho has observed someplants with deep red, violet orbrown leaves. He wants toknow whether these leavesalso carry out photosynthesis.Stomatal opening(c) StomataFig. 1.2Activity 1.1Take two potted plants of the same kind.Keep one in the dark (or in a black box)for 72 hours and the other in theNUTRITIONIN PLANTS3

www.GOALias.blogspot.comsunlight. Perform iodine test with theleaves of both the plants as you did inClass VI. Record your results. Now leavethe pot which was earlier kept in thedark, in the sunlight for 3 – 4 days andperform the iodine test again on itsleaves. Record your observations in yournotebook.The leaves other than green also havechlorophyll. The large amount of red,brown and other pigments mask thegreen colour (Fig. 1.4). Photosynthesistakes place in these leaves also.Fig. 1.4 Leaves of various coloursYou often see slimy, green patchesin ponds or in other stagnant waterbodies. These are generally formed bythe growth of organisms called algae.Can you guess why algae are green incolour? They contain chlorophyll whichgives them the green colour. Algae canalso prepare their own food byphotosynthesis.Synthesis of plant food otherthan carbohydratesYou have just learnt that plantssynthesise carbohydrates through theprocess of photosynthesis. Thecarbohydrates are made of carbon,hydrogen and oxygen. These are usedto synthesise other components of food.But proteins are nitrogenous substanceswhich contain nitrogen. From where dothe plants obtain nitrogen?Recall that nitrogen is present inabundance in gaseous form in the air.However, plants cannot absorb nitrogenin this form. Soil has certain bacteriathat convert gaseous nitrogen into ausable form and release it into the soil.These soluble forms are absorbed by theplants along with water. Also, you mighthave seen farmers adding fertilisers richin nitrogen to the soil. In this way theplants fulfil their requirements ofnitrogen along with the otherconstituents. Plants can thensynthesise components of food otherthan carbohydrates such as proteinsand fats.1.3 OTHERMODESOF NUTRITIONINPLANTSThere are some plants which do not havechlorophyll. They cannot synthesisetheir food. How do they survive and fromwhere do they derive nutrition? Likehumans and animals such plantsdepend on the food produced by otherplants. They use the heterotrophicmode of nutrition. Look at Fig. 1.5. Doyou see yellow tubular structurestwining around the stem and branchesof a tree? This is a plant called Cuscuta(Amarbel). It does not have chlorophyll.It takes readymade food from the plant4SCIENCE

www.GOALias.blogspot.comstructure is the modified part of the leaf.The apex of the leaf forms a lid whichcan open and close the mouth of thepitcher. Inside the pitcher there are hairwhich are directed downwards. Whenan insect lands in the pitcher, the lidcloses and the trapped insect getsentangled into the hair. The insect isdigested by the digestive juices secretedin the pitcher. Such insect-eating plantsare called insectivorous plants.Is it possible that such plants do notget all the required nutrients from thesoil in which they grow?Fig. 1.5 Cuscuta (Amarbel) on host planton which it is climbing. The plant onwhich it climbs is called a host. Since itdeprives the host of valuable nutrients,it is called a parasite. Are we and theother animals also parasites for theplants? You should think about it anddiscuss with your teacher.Boojho is confused. If thepitcher plant is green andcarries out photosynthesis, thenwhy does it feed on insects?LidPaheli wants to know whethermosquitoes, bed bugs, lice andleeches that suck our blood arealso parasites.Have you seen or heard of plants thatcan eat animals? There are a few plantswhich can trap insects and digest them.Is it not amazing? Such plants may begreen or of some other colour. Look atthe plant in Fig. 1.6. The pitcher-likeLeaf modifiedinto pitcherFig. 1.6 Pitcher plant showing lid and pitcherNUTRITIONIN PLANTS5

www.GOALias.blogspot.com1.4 S1.4 SAPROTROPHSYou might have seen packets ofmushrooms sold in the vegetablemarket. You may have also seen fluffyumbrella-like patches growing on rottingwood during the rainy season (Fig. 1.7).Let us find out what type of nutrientsthey need to survive and from wherethey get them.Fig. 1.7 Packet of mushrooms, a mushroomgrowing on decayed materialBoojho wants to know howthese organisms acquirenutrients. They do not havemouths like animals do. They arenot like green plants as they lackchlorophyll and cannot make foodby photosynthesis.Fig. 1.8 Fungigrowing on breadWrite down your observations in yournotebook. Most probably you will seecotton-like threads spread on the pieceof bread.These organisms are called fungi.They have a different mode of nutrition.They secrete digestive juices on the deadand decaying matter and convert it intoa solution. Then they absorb thenutrients from it. This mode of nutritionin which organisms take in nutrients insolution form from dead and decayingmatter is called saprotrophic nutrition.Plants which use saprotrophic mode ofnutrition are called saprotrophs.Fungi also grow on pickles, leather,clothes and other articles that are leftin hot and humid weather for long time.Activity 1.2Take a piece of bread and moisten it withwater. Leave it in a moist warm placefor 2–3 days or until fluffy patchesappear on them (Fig. 1.8). These patchesmay be white, green, brown or of anyother colour. Observe the patches undera microscope or a magnifying glass.Paheli is keen to knowwhether her beautiful shoes,which she wore on specialoccasions, were spoiled by fungiduring the rainy season. Shewants to know how fungi appearsuddenly during the rainyseason.6SCIENCE

www.GOALias.blogspot.comBoojho says once hisgrandfather told him that hiswheat fields were spoiled by afungus. He wants to know iffungi cause diseases also.Paheli told him that many fungilike yeast and mushrooms areuseful, but some fungicause diseases in plants,animals and humans.Some fungi are also usedin medicines.During the rainy season they spoil manythings. Ask your parents about themenace of fungi in your house.The fungal spores are generallypresent in the air. When they land onwet and warm things they germinateand grow. Now, can you figure out howwe can protect our things from gettingspoiled?Some organisms live together andshare shelter and nutrients. This iscalled symbiotic relationship. Forexample, certain fungi live in the rootsof trees. The tree provides nutrients tothe fungus and, in return, receives helpfrom it to take up water and nutrientsfrom the soil. This association is veryimportant for the tree.In organisms called lichens, achlorophyll-containing partner, which isan alga, and a fungus live together. Thefungus provides shelter, water andminerals to the alga and, in return, thealga provides food which it prepares byphotosynthesis.1.51.5 HOWNUTRIENTSAREREPLENISHEDIN THE SOILHave you seen farmers spreadingmanure or fertilisers in the fields, orgardeners using them in lawns or inpots? Do you know why they are addedto the soil?You learnt that plants absorbmineral nutrients from the soil. So, theiramounts in the soil keep on declining.Fertilisers and manures contain plantnutrients such as nitrogen, potassium,phosphorous, etc. These nutrients needto be added from time to time to enrichthe soil. We can grow plants and keepthem healthy if we can find out thenutrient requirement of plants.Usually crops require a lot of nitrogento make proteins. After the harvest, thesoil becomes deficient in nitrogen.Though nitrogen gas is available inplenty in the air, plants cannot use it inthe manner they can use carbon dioxide.They need nitrogen in a soluble form.The bacterium called Rhizobium cantake atmospheric nitrogen and convertit into a soluble form. But Rhizobiumcannot make its own food. So it lives inthe roots of gram, peas, moong beansand other legumes and provides themwith nitrogen. Most of the pulses (dals)are obtained from leguminous plants.In return, the plants provide food andshelter to the bacteria. They have aNUTRITIONIN PLANTS7

www.GOALias.blogspot.comsymbiotic relationship. This associationis of great significance for the farmers.They do not need to add nitrogenfertiliser to the soil in which leguminousplants are grown.In this chapter you learnt thatmost of the plants are autotrophs.Only a few plants adopt other modesof nutrition like parasitic andsaprotrophic. They derive nutritionfrom other organisms. All animalsare categorised as heterotrophs sincethey depend on plants and otheranimals for food. Can we say thatthe insectivorous plants are partialheterotrophs?KeywordsAutotrophicChlorophyllHeterotrophsHostInsectivorousNutrientNutritionParasitePhotosynthesisSaprotrophsSaprotrophicStomataWhat you have learnt• All organisms take food and utilise it to get energy for the growth andmaintenance of their bodies.• Green plants synthesise their food themselves by the process ofphotosynthesis. They are autotrophs.• Plants use simple chemical substances like carbon dioxide, water andminerals for the synthesis of food.• Chlorophyll and sunlight are the essential requirements forphotosynthesis.• Complex chemical substances such as carbohydrates are the productsof photosynthesis.• Solar energy is stored by the leaves with the help of chlorophyll.• Oxygen is produced during photosynthesis.• Oxygen released in photosynthesis is utilised by other living organismsfor their survival.• Fungi derive nutrition from dead, decaying matter. They are saprotrophs.Plants like cuscuta are parasites. They take food from the host plant.• A few plants and all animals are dependent on others for their nutritionand are called heterotrophs.8SCIENCE

www.GOALias.blogspot.comExercise1. Why do organisms need to take food?2. Distinguish between a parasite and a saprotroph.3. How would you test the presence of starch in leaves?4. Give a brief description of the process of synthesis of food in green plants.5. Show with the help of a sketch that the plants are the ultimate sourceof food.6. Fill in the blanks:(a) Green plants are called _________________ since they synthesisetheir own food.(b) The food synthesised by the plants is stored as _________________.(c) In photosynthesis solar energy is captured by the pigment called___________.(d) During photosynthesis plants take in ______________________ andrelease __________________.7. Name the following:(i) A parasitic plant with yellow, slender and tubular stem.(ii) A plant that has both autotrophic and heterotrophic mode of nutrition.(iii) The pores through which leaves exchange gases.8. Tick the correct answer:(a) Amarbel is an example of:(i) autotroph (ii) parasite (iii) saprotroph (iv) host(b) The plant which traps and feeds on insects is:(i) cuscuta (ii) china rose (iv) pitcher plant (iv) rose9. Match the items given in Column I with those in Column II:Column IColumn IIChlorophyllNitrogenAmarbelBacteriaHeterotrophsPitcher plantAnimalsLeafInsectsParasite10. Mark ‘T’ if the statement is true and ‘F’ if it is false:(i) Carbon dioxide is released during photosynthesis. (T/F)NUTRITIONIN PLANTS9

www.GOALias.blogspot.com(ii)(iii)(iv)Plants which synthesise their food themselves are calledsaprotrophs. (T/F)The product of photosynthesis is not a protein. (T/F)Solar energy is converted into chemical energy duringphotosynthesis. (T/F)11. Choose the correct option from the following:Which part of the plant gets carbon dioxide from the air for photosynthesis.(i) root hair (ii) stomata (iii) leaf veins (iv) sepals12. Choose the correct option from the following:Plants take carbon dioxide from the atmosphere mainly through their:(i) roots (ii) stem (iii) flowers (iv) leavesExtended Learning — Activities and Projects1. ProjectTake a potted plant with broadleaves. Take two strips of blackpaper and cut out a small squarein their centres. Cover a part of twoleaves with these papers and securethem with paper clips (Fig. 1.9).Keep the plant in the sunlight for2–5 days. Observe the difference inthe colour of the covered and theuncovered portions on the one leaf.Perform iodine test on this leaf. Didthe two parts show any differenceFig. 1.9 Experiment to test thein results? Now take another leaf. occurrence of photosynthesisRemove the strip and expose thecovered part to the sunlight for 2–3 days and do the iodine test again.Describe your observations.2. Visit a green house if there is one near your place. Observe how theyraise plants. Find out how they regulate the light, water and carbondioxide.3. Try growing a sweet potato just in water. Describe your experiment andobservations.You can read more on the following website:www.phschool.com/science/biology_place/biocoach/photosynth/overview.htmDid you know?Light is so important to plants that their leaves grow in many patterns soas to catch the most sunlight.10SCIENCE

www.GOALias.blogspot.com2Nutrition in AnimalsYou have learnt in Chapter 1 thatplants can prepare their own foodby the process of photosynthesisbut animals cannot. Animals get theirfood from plants, either directly byeating plants or indirectly by eatinganimals that eat plants. Some animalseat both plants and animals. Recall thatall organisms including humans requirefood for growth, repair and functioningof the body. Animal nutrition includesnutrient requirement, mode of intakeof food and its utilisation in the body.You have studied in Class VI that foodconsists of many components. Try torecall and list them below:1. ______________________2. ______________________3. ______________________4. ______________________5. ______________________6. ______________________The components of food such ascarbohydrates are complex substances.These complex substances cannot beutilised as such. So they are brokendown into simpler substances. Thebreakdown of complex components ofComplex substanceSimpler substancesfood into simpler substances is calleddigestion.2.12.1 DIFFERENTWAYSOF TAKINGFOODThe mode of taking food into the bodyvaries in different organisms. Bees andhumming-birds suck the nectar ofplants, infants of human and manyother animals feed on mother’s milk.Snakes like the python swallow theanimals they prey upon. Some aquaticanimals filter tiny food particles floatingnearby and feed upon them.Activity 2.1What is the type of food and mode offeeding of the following animals? Writedown your observations in the givenTable. You may find the list of modes offeeding given below the Table helpful.Table 2.1 Various modes of feedingName ofKind ofMode ofanimalfoodfeedingSnailAntEagleHumming-birdLiceMosquitoButterflyHouse fly(Scraping, chewing, brewing, capturingand swallowing, sucking etc.)

www.GOALias.blogspot.comAmazing factStarfish feeds on animals covered byhard shells of calcium carbonate.After opening the shell, the starfishpops out its stomach through itsmouth to eat the soft animal insidethe shell. The stomach then goes backinto the body and the food is slowlydigested.of the stomach and the small intestine,and the various glands such as salivaryglands, the liver and the pancreassecrete digestive juices. The digestivejuices convert complex substances ofBuccal cavityOesophagusSalivary glandLiverFig. 2.1 StarfishGall bladderStomach2.2 D2.2 DIGESTIONIN HUMANSWe take in food through the mouth,digest and utilise it. The unused partsof the food are defecated. Have you everwondered what happens to the foodinside the body? The food passesthrough a continuous canal (Fig. 2.2)which begins at the buccal cavity andends at the anus. The canal can bedivided into various compartments:(1) the buccal cavity, (2) foodpipe oroesophagus, (3) stomach, (4) smallintestine, (5) large intestine ending inthe rectum and (6) the anus. Is it not avery long path? These parts togetherform the alimentary canal (digestivetract). The food components graduallyget digested as food travels through thevarious compartments. The inner wallsFig. 2.2 Human digestive systemPancreasSmallintestineLargeintestineRectumAnusfood into simpler ones. The digestivetract and the associated glands togetherconstitute the digestive system.Now, let us know what happens tothe food in different parts of the digestivetract.The mouth and buccal cavityFood is taken into the body through themouth. The process of taking food into12SCIENCE

www.GOALias.blogspot.comMilk teeth and permanent teethDo you remember about falling of your teeth some years ago? The first set ofteeth grows during infancy and they fall off at the age between six to eightyears. These are termed milk teeth. The second set that replaces them are thepermanent teeth. The permanent teeth may last throughout life or fall offduring old age.MolarBoojho is fascinated by thehighly coiled small intestine seenin Fig. 2.2. He wants to know itslength. Would you like to make awild guess? We have given itsapproximate length on page 16.Just imagine how such a longstructure is accommodated in asmall space within our body!PremolarCanineIncisorthe body is called ingestion. We chewFig. 2.3 Arrangement of teeth and differentthe food with the teeth and break it downtype of teethmechanically into small pieces. Eachtooth is rooted in a separate socket in which ones for piercing and tearing?the gums (Fig. 2.3). Our teeth vary in Also find out the ones that are used forappearance and perform different chewing and grinding?functions. Accordingly they are given Record your observations in Table 2.2different names (Fig. 2.3).Table 2.2Activity 2.2Type of teethNumber of teethTotalWash your hands. Look into theLower jawUpper jawmirror and count your teeth. Use Cutting andyour index finger to feel the teeth. biting teethHow many kinds of teeth could you Piercing andfind? Take a piece of an apple or tearing teethbread and eat it. Which teeth do Chewing andyou use for biting and cutting, and grinding teethNUTRITIONIN ANIMALS1313

www.GOALias.blogspot.comOur mouth has the salivary glandswhich secrete saliva. Do you know theaction of saliva on food? Let us find out.Activity 2.3Take two test tubes. Label them ‘A’ and‘B’. In test tube ‘A’ put one teaspoonfulAIodine solutionBoiled riceWaterBoiled and chewed riceBFig. 2.4 Effect of saliva on starchof boiled rice; in test tube ‘B’ keep oneteaspoonful of boiled rice after chewingit for 3 to 5 minutes. Add 3–4 mL ofwater in both the test tubes (Fig. 2.4).Now pour 2–3 drops of iodine solutionin each test tube and observe. Why isthere a change in colour in the testtubes? Discuss the results with yourclassmates and your teacher. The salivabreaks down the starch into sugars.The tongue is a fleshy muscularorgan attached at the back to the floorof the buccal cavity. It is free at the frontand can be moved in all directions. Doyou know the functions of the tongue?We use our tongue for talking. Besides,it mixes saliva with the food duringchewing and helps in swallowing food.We also taste food with our tongue. Ithas taste buds that detect differenttastes of food. We can find out theSweets and tooth decayNormally bacteria are present in our mouth but they are not harmfulto us. However, if we do not clean our teeth and mouth after eating,many harmful bacteria also begin to live and grow in it. These bacteriabreak down the sugars present from the leftover food and releaseacids (see Chapter 5 to know what an acid is). The acids graduallydamage the teeth (Fig. 2.5). This is called tooth decay. If it is nottreated in time, it causes severe toothache and in extreme casesresults in tooth loss. Chocolates, sweets, cold drinks and other sugarproducts are the major culprits of tooth decay.Therefore, one should clean the teeth with a brush or dantunand dental floss (a special strong thread which is moved betweentwo teeth to take out trapped food particles) at least twice a day andrinse the mouth after every meal. Also, one should not put dirtyfingers or any unwashed object in the mouth.(a)(b)(c)(d)Fig. 2.5 Gradual decay of tooth14SCIENCE

www.GOALias.blogspot.comSometimes when you eat in a hurry, talk or laugh while eating, you may gethiccups or a choking sensation. This happens when food particles enter thewindpipe. The windpipe carries air from the nostrils to the lungs. It runs adjacentto the foodpipe. But inside the throat, air and food share a common passage.Then how is food prevented from entering the windpipe? During the act ofswallowing a flap-like valve closes the passage of the windpipe and guides thefood into the foodpipe. If, by chance, food particles enter the windpipe, we feelchoked or get hiccups.Fig. 2.6 Regions of thetongue for different tastes5. Now write down your observationsand label Fig. 2.6.Repeat this activity with otherclassmates.The foodpipe/oesophagusThe swallowed food passes into thefoodpipe or oesophagus. Look at Fig. 2.2.The foodpipe runs along the neckposition of taste buds by the followingactivity.Activity 2.41. Prepare a separate sample each of(i) sugar solution, (ii) common saltsolution, (iii) lemon juice and (iv) juiceof crushed neem leaf or bitter gourd.2. Blindfold one of your classmates andask her/him to take out the tongueand keep it in straight and flat position.3. Use a clean toothpick to put theabove samples one by one ondifferent areas of the tongue asshown in Fig. 2.6. Use a newtoothpick for each sample.4. Ask the classmate which areas of thetongue could detect the sweet, salty,sour and bitter substances.Paheli wants to know howfood moves in the oppositedirection during vomiting.FoodAlimentary canalStomachFig. 2.7 Movement of thefood in the alimentary canalNUTRITIONIN ANIMALS1515

www.GOALias.blogspot.comand the chest. Food is pushed down bymovement of the wall of the foodpipe.Actually this movement takes placethroughout the alimentary canal andpushes the food downwards (Fig. 2.7).At times the food is not accepted by ourstomach and is vomited out. Recall theinstances when you vomited after eatingand think of the reason for it. Discusswith your parents and teacher.The stomachThe stomach is a thick-walled bag. Itsshape is like a flattened U and it is thewidest part of the alimentary canal. Itreceives food from the food pipe at oneend and opens into the small intestineat the other.The inner lining of the stomachsecretes mucous, hydrochloric acid anddigestive juices. The mucous protectsthe lining of the stomach. The acid killsmany bacteria that enter along with thefood and makes the medium in thestomach acidic. The digestive juicesbreak down the proteins into simplersubstances.The small intestineThe small intestine is highly coiled andis about 7.5 metres long. It receivessecretions from the liver and thepancreas. Besides, its wall also secretesjuices.The liver is a reddish brown glandsituated in the upper part of theabdomen on the right side. It is thelargest gland in the body. It secretes bilejuice that is stored in a sac called thegall bladder (Fig. 2.2). The bile playsan important role in the digestion of fats.The pancreas is a large creamcoloured gland located just below thestomach (Fig. 2.2). The pancreatic juiceacts on carbohydrates and proteins andchanges them into simpler forms. TheThe working of the stomach was discovered by astrange accident. In 1822, a man named Alexis St.Martin was badly hit by a shot gun. The bullet hadseriously damaged the chest wall and made a holein his stomach. He was brought to an Americanarmy doctor William Beaumont. The doctor savedthe patient but he could not close the hole properly(Fig. 2.8). Beaumont took it as a great opportunityto see the inside of the stomach through the hole.He made some wonderful observations.Beaumont found that the stomach was churningFig. 2.8 Alexis St. Martin’sfood. Its wall secreted a fluid which could digestshotgun woundthe food. He also observed that the end of thestomach opens into the intestine only after the digestion of the food inside thestomach is completed.16SCIENCE

www.GOALias.blogspot.compartly digested food now reaches thelower part of the small intestine wherethe intestinal juice completes thedigestion of all components of the food.The carbohydrates get broken intosimple sugars such as glucose, fats intofatty acids and glycerol, and proteinsinto amino acids.Absorption in the smallintestineThe digested food can now pass into theblood vessels in the wall of the intestine.This process is called absorption. Theinner walls of the small intestine havethousands of finger-like outgrowths.These are called villi (singular villus).Can you guess what the role of villi couldbe in the intestine? The villi increasethe surface area for absorption of thedigested food. Each villus has a networkof thin and small blood vessels close toits surface. The surface of the villiabsorbs the digested food materials. Theabsorbed substances are transportedvia the blood vessels to different organsof the body where they are used to buildcomplex substances such as theproteins required by the body. This iscalled assimilation. In the cells, glucosebreaks down with the help of oxygen intocarbon dioxide and water, and energyis released. The food that remainsundigested and unabsorbed then entersinto the large intestine.Large intestineThe large intestine is wider and shorterthan small intestine. It is about 1.5 metrein length. Its function is to absorb waterand some salts from the undigested foodmaterial. The remaining waste passesinto the rectum and remains there assemi-solid faeces. The faecal matter isremoved through the anus fromtime-to-time. This is called egestion.2.32.3 DIGESTIONIN GRASSRASS-EATINGANIMALSHave you observed cows, buffaloes andother grass-eating animals chewingcontinuously even when they are noteating grass? Actually, they quicklyswallow the grass and store it in aseparate part of the stomach calledrumen (Fig. 2.9). Here the food getsDiarrhoeaSometime you may have experienced the need to pass watery stool frequently.This condition is known as diarrhoea. It may be caused by an infection, foodpoisoning or indigestion. It is very common in India, particularly among children.Under severe conditions it can be fatal. This is because of the excessive loss ofwater and salts from the body. Diarrhoea should not be neglected. Even before adoctor is consulted the patient should be given plenty of boiled and cooled waterwith a pinch of salt and sugar dissolved in it. This is called Oral RehydrationSolution (ORSORS).NUTRITIONIN ANIMALS1717

www.GOALias.blogspot.comPaheli wants to know whythese animals cannot chewfood properly at the time theytake it in?Boojho wants to know whywe cannot digest celluloselike the cattle do.partially digested and is called cud. Butlater the cud returns to the mouth insmall lumps and the animal chews it.This process is called rumination andthese animals are called ruminants.The grass is rich in cellulose, a typeof carbohydrate. Many animals,including humans, cannot digestcellulose.RumenRuminants have a large sac-likestructure between the small intestineand large intestine (Fig. 2.9). Thecellulose of the food is digested here bythe action of certain bacteria which arenot present in humans.So far you have learnt about animalswhich possess the digestive system. Butthere are many small organisms whichdo not have a mouth and a digestivesystem. Then, how do they acquire anddigest food? In the section below you willlearn another interesting way of foodintake.2.4 FEEDINGAND DIGESTIONINAMOEBAAmoeba is a microscopic single-celledorganism found in pond water. Amoebahas a cell membrane, a rounded, densenucleus and many small bubble-likevacuoles (Fig. 2.10) in its cytoplasm.Amoeba constantly changes its shapeand position. It pushes out one, ormore finger-like projections, calledpseudopodia or false feet for movementand capture of food.Amoeba feeds on some microscopicorganisms. When it senses food, itNucleusPseudopodiumFood particle(ingestion)StomachFig. 2.9 Digestive system of ruminantFood vacuoleFig. 2.10 AmoebaEgested waste18SCIENCE

www.GOALias.blogspot.compushes out pseudopodia around thefood particle and engulfs it. The foodbecomes trapped in a food vacuole[Fig. 2.10).Digestive juices are secreted into thefood vacuole. They act on the food andbreak it down into simpler substances.Gradually the digested food is absorbed.The absorbed substances are used forgrowth, maintenance and multiplication.The undigested residue of the food isexpelled outside by the vacuole.The basic process of digestion offood and release of energy is the samein all animals. In a later chapter youwill learn about the transport of foodabsorbed by the intestine to the variousparts of the body.KeywordsAbsorptionAmino acidAmoebaAssimilationBileBuccal cavityCanineCelluloseDigestionEgestionFatty acidFood vacuoleGall bladderGlycerolIncisorIngestionLiverMilk teethMolarPermanent teethOesophagusPancreasPremolarPseudopodiaRumenRuminantRuminationSalivary glandsVilliSalivaWhat you have learnt• Animal nutrition includes nutrient requirement, mode of intake of foodand its utilisation in the body.• The human digestive system consists of the alimentary canal andsecretory glands. It consists of the (i) buccal cavity, (ii) oesophagus,(iii) stomach, (iv) small intestine, (v) large intestine ending in rectumand (vi) anus. The main digestive glands which secrete digestive juicesare (i) the salivary glands, (ii) the liver and (iii) the pancreas. The stomachwall and the wall of the small intestine also secrete digestive juices.• The modes of feeding vary in different organisms.• Digestion is a complex process involving: (i) ingestion, (ii) digestion,(iii) absorption, (iv) assimilation and (v) egestion.NUTRITIONIN ANIMALS1919

www.GOALias.blogspot.com• Digestion of carbohydrates, like starch, begins in the buccal cavity. Thedigestion of protein starts in the stomach. The bile secreted from theliver, the pancreatic juice from the pancreas and the digestive juice fromthe intestinal wall complete the digestion of all components of food inthe small intestine. The digested food is absorbed in the blood vessels inthe small intestine.• The absorbed substances are transported to different parts of the body.Water and some salts are absorbed from the undigested food in thelarge intestine.• The undigested and unabsorbed residues are expelled out of the bodyas faeces through the anus.• The grazing animals like cows, buffaloes and deer are known asruminants. They quickly ingest, swallow their leafy food and store it inthe rumen. Later, the food returns to the mouth and the animal chewsit peacefully.• Amoeba ingests its food with the help of its false feet or pseudopodia.The food is digested in the food vacuole.Exercises1. Fill in the blanks:(a) The main steps of digestion in humans are __________, __________,__________, _________ and __________.(b) The largest gland in the human body is __________.(c) The stomach releases hydrochloric acid and ___________ juices whichact on food.(d) The inner wall of the small intestine has many finger-like outgrowthscalled _________.(e) Amoeba digests its food in the ____________ .2. Mark ‘T’ if the statement is true and ‘F’ if it is false:(a) Digestion of starch starts in the stomach. (T/F)(b) The tongue helps in mixing food with saliva. (T/F)(c) The gall bladder temporarily stores bile. (T/F)(d) The ruminants bring back swallowed grass into their mouthand chewit for some time. (T/F)3. Tick () mark the correct answer in each of the following:(a) Fat is completely digested in the(i) stomach (ii) mouth (iii) small intestine (iv) large intestine20SCIENCE

www.GOALias.blogspot.com(b) Water from the undigested food is absorbed mainly in the(i) stomach (ii) foodpipe (iii) small intestine(iv) large intestine4. Match the items of Column I with those given in Column II:Column IFood componentsColumn IIProduct(s) of digestionCarbohydratesFatty acids and glycerolProteinsSugarFatsAmino acids5. What are villi? What is their location and function?6. Where is the bile produced? Which component of the food does it digest?8. Name the type of carbohydrate that can be digested by ruminants butnot by humans. Give the reason also.9. Why do we get instant energy from glucose?10. Which part of the digestive canal is involved in:(i) absorption of food ________________.(ii) chewing of food ________________.(iii) killing of bacteria ________________.(iv) complete digestion of food ________________.(v) formation of faeces ________________.11. Write one similarity and one difference between the nutrition in amoebaand human beings.12. Match the items of Column I with suitable items in Column IIColumn IColumn II(a) Salivary gland (i) Bile juice secretion(b) Stomach (ii) Storage of undigested food(c) Liver (iii) Saliva secretion(d) Rectum (iv) Acid release(e) Small intestine (v) Digestion is completed(f ) Large intestine (vi) Absorption of water(vii)Release of faecesNUTRITIONIN ANIMALS2121

www.GOALias.blogspot.com13. Label Fig. 2.11 of the digestive system.Fig. 2.11 Human digestive system14. Can we survive only on raw, leafy vegetables/grass? Discuss.Extended Learning — Activities and Project1. Visit a doctor and find out:(i)(ii)Under what conditions does a patient need to be on a drip ofglucose?Till when does a patient need to be given glucose?(iii) How does glucose help the patient recover?Write the answers in your notebook.2. Find out what vitamins are and get the following information.(i) Why are vitamins necessary in the diet?(ii) Which fruits or vegetables should be eaten regularly to getvitamins?Write a one-page note on the information collected by you. You may takehelp of a doctor, a dietician, your teacher or any other person, or fromany other source.22SCIENCE

www.GOALias.blogspot.com3. Collect data from your friends, neighbours and classmates to know moreabout “milk teeth”.Tabulate your data. One way of doing it is given below:S. No. Age at whichfirst tooth fell1.2.3.4.5.Age at whichlast tooth fellNo. of teethlostNo. of teethreplacedFind out from at least twenty children and find the average age at whichchildren lose the milk teeth. You may take help of your friends.You can read more on the following website:www.health.howstuffworks.com/adam-200142.htmDid you know?That fats in goat’s milk are much simpler than those in cow’s milk.Therefore, the goat’s milk is much easier to digest than the cow’s milk.NUTRITIONIN ANIMALS2323

www.GOALias.blogspot.com3Fibre to FabricIn Class VI you have learnt aboutsome fibres obtained from plants.You also learnt that wool and silkfibres are obtained from animals. Woolis obtained from the fleece (hair) ofsheep or yak. Silk fibres come fromcocoons of the silk moth. Do you knowwhich part of the sheep’s body yieldsfibres? Are you aware how these fibresare converted into the woollen yarn thatwe buy from the market to knit sweaters?Do you have any idea how silk fibres aremade into silk, which is woven into saris?In this Chapter we shall try to findanswers to these questions.Animal fibres — wool and silk3.1 W3.1 WOOLWool comes from sheep, goat, yak andsome other animals. These wool-yieldinganimals bear hair on their body. Do youknow why these animals have a thickcoat of hair? Hair trap a lot of air. Air isa poor conductor of heat, as you wouldlearn in Chapter 4. So, hair keeps theseanimals warm. Wool is derived fromthese hairy fibres.Activity 3.1Feel the hair on your body and armsand those on your head. Do you findany difference? Which one seems coarseand which one is soft?Like us, the hairy skin of the sheephas two types of fibres that form itsfleece: (i) the coarse beard hair, and(ii) the fine soft under-hair close to theskin. The fine hair provide the fibres formaking wool. Some breeds of sheeppossess only fine under-hair. Theirparents are specially chosen to give birthto sheep which have only soft underhair.This process of selecting parentsfor obtaining special characters in theiroffspring, such as soft under hair insheep, is termed ‘selective breeding’.Fig. 3.1 Sheep with thick growth of hairAnimals that yield woolSeveral breeds of sheep are found indifferent parts of our country (Table 3.1).However, the fleece of sheep is not theonly source of wool, though woolcommonly available in the market is24SCIENCE

www.GOALias.blogspot.comsheep wool (Fig. 3.1). Yak (Fig. 3.2) woolis common in Tibet and Ladakh. Angorawool is obtained from angora goats,(Fig. 3.3) found in hilly regions such asJammu and Kashmir.Wool is also obtained from goat hair(Fig. 3.4). The under fur of Kashmirigoat is soft. It is woven into fine shawlscalled Pashmina shawls.The fur (hair) on the body of camelsis also used as wool (Fig. 3.5). Llamaand Alpaca, found in South America,also yield wool (Fig. 3.6 and 3.7).Activity 3.2Collect pictures of animals whose hairis used as wool. Stick them in your scrapbook. If you are unable to get pictures,try and draw them from the ones givenin this book.Find out words for sheep, goat, cameland yak in your local language and alsoin other languages of our country.Activity 3.3Procure outline maps of India and theworld. Find out and mark the places onthe map where you find animals thatprovide wool. Use different colours todenote the location for different woolyielding animals.Fig. 3.3 Angora goat Fig. 3.4 GoatFig. 3.5 CamelFig. 3.2 YakFig. 3.6 LlamaFig. 3.7 AlpacaFIBRETO FABRIC2525

www.GOALias.blogspot.comFrom fibres to woolFor obtaining wool, sheep are reared.Their hair is cut and processed intowool. Let us learn about this process.Rearing and breeding of sheep: If youtravel to the hills in Jammu & Kashmir,Himachal Pradesh, Uttaranchal,Arunachal Pradesh and Sikkim, or theplains of Haryana, Punjab, Rajasthanand Gujarat, you can see shepherdstaking their herds of sheep for grazing.Sheep are herbivores and prefer grassand leaves. Apart from grazing sheep,rearers also feed them on a mixture ofpulses, corn, jowar, oil cakes (materialleft after taking out oil from seeds) andminerals. In winter, sheep are keptindoors and fed on leaves, grain and dryfodder.Sheep are reared in many parts ofour country for wool. Table 3.1 gives thenames of some breeds of sheep rearedin our country for producing wool. Thequality and texture of the fibres obtainedfrom them is also indicated in the table.Certain breeds of sheep have thickcoat of hair on their body which yieldsgood quality wool in large quantities. Asmentioned earlier, these sheep are“selectively bred” with one parent beinga sheep of good breed.Once the reared sheep havedeveloped a thick growth of hair, hair isshaved off for getting wool.Processing fibres into woolThe wool which is used for knittingsweaters or for weaving shawls is thefinished product of a long process,which involves the following steps:Step I: The fleece of the sheep along with athin layer of skin is removed from itsbody [Fig. 3.8 (a)]. This process is calledshearing. Machines similar to those usedby barbers are used to shave off hair.Usually, hair are removed during the hotweather. This enables sheep to survivewithout their protective coat of hair. Thehair provide woollen fibres. Woollenfibres are then processed to obtainwoollen yarn. Shearing does not hurtthe sheep just as it does not hurt whenyou get a hair cut or your father shaves hisbeard. Do you know why? The uppermostlayer of the skin is dead. Also, the hair ofsheep grow again just as your hair does.Table 3.1 Some Indian breeds of sheepS.No. Name of breed Quality of wool State where found1. Lohi Good quality wool Rajasthan, Punjab2. Rampur bushair Brown fleece Uttar Pradesh,Himachal Pradesh3. Nali Carpet wool Rajasthan, Haryana, Punjab4. Bakharwal For woollen shawls Jammu and Kashmir5. Marwari Coarse wool Gujarat6. Patanwadi For hosiery Gujarat26SCIENCE

www.GOALias.blogspot.comStep II: The sheared skin with hair isthoroughly washed in tanks to removegrease, dust and dirt. This is calledscouring. Nowadays scouring is doneby machines [Fig. 3.8 (b) and (c)].Step III: After scouring, sorting is done.The hairy skin is sent to a factory wherehair of different textures are separatedor sorted.Step IV: The small fluffy fibres, calledburrs, are picked out from the hair.These are the same burrs whichsometimes appear on your sweaters. Thefibres are scoured again and dried. Thisis the wool ready to be drawn into fibres.Step V: The fibres can be dyed in variouscolours, as the natural fleece of sheepand goats is black, brown or white.Step VI: The fibres are straightened,combed and rolled into yarn[Fig. 3.8 (d)]. The longer fibres aremade into wool for sweaters and theshorter fibres are spun and woveninto woollen cloth.Fig. 3.8 (a) Shearing a sheepFig. 3.8 (b) Scouring in tanksFig. 3.8 (c) Scouring by machinesFig. 3.8 (d) Rolling into yarnFIBRETO FABRIC2727

www.GOALias.blogspot.comOccupational hazardWool industry is an importantmeans of livelihood for many peoplein our country. But sorter’s job isrisky as sometimes they get infectedby a bacterium, anthrax, whichcauses a fatal blood disease calledsorter’s disease. Such risks faced byworkers in any industry are calledoccupational hazards.Boojho is wondering why ithurts when someone pulls hishair but not when he goes for ahaircut.your mother/aunt/grandmother thekind of silk saris they have. List thekinds of silk.Before we discuss the process ofobtaining silk, it is necessary to know theinteresting life history of the silk moth.Life history of silk mothThe female silk moth lays eggs, fromwhich hatch larvae which are calledcaterpillars or silkworms. They grow insize and when the caterpillar is ready toenter the next stage of its life historycalled pupa, it first weaves a net to holditself. Then it swings its head from sideto side in the form of the figure of eight (8).During these movements of the head,the caterpillar secretes fibre made of aBoojho is wondering why acotton garment cannot keep usas warm in winter as a woollensweater does.(a) Male (b) FemaleAdult silk mothsActivity 3.4Debate amongst your classmateswhether it is fair on the part of humansto rear sheep and then chop off theirhair for getting wool.3.2 S3.2 SILKSilk fibres are also animal fibres.Silkworms spin the ‘silk fibres’. Therearing of silkworms for obtaining silkis called sericulture. Find out from(c) Eggs on mulberry leaves (d) Silkworm(e) Cocoon (f) Cocoon with developing mothFig. 3.9 (a to f ) Life history of silk moth28SCIENCE

www.GOALias.blogspot.comprotein which hardens on exposure toair and becomes silk fibre. Soon thecaterpillar completely covers itself by silkfibres. This covering is known ascocoon. The further development of themoth continues inside the cocoon(Fig. 3.9). Silk fibres are used forweaving silk cloth. Can you imagine thatthe soft silk yarn is as strong as acomparable thread of steel!The silk yarn (thread) is obtainedfrom the cocoon of the silk moth. Thereis a variety of silk moths which look verydifferent from one another and the silkyarn they yield is different in texture(coarse, smooth, shiny, etc.). Thus,tassar silk, mooga silk, kosa silk, etc.,are obtained from cocoons spun bydifferent types of moths. The mostcommon silk moth is the mulberry silkmoth. The silk fibre from the cocoon ofthis moth is soft, lustrous and elasticand can be dyed in beautiful colours.Sericulture or culture of silkwormsis a very old occupation in India. Indiaproduces plenty of silk on a commercialscale.Activity 3.5Collect pieces of silk cloth of varioustypes and paste them in your scrapbook. You can find them in a tailor’sshop among the heap of waste cut pieces.Take help of your mother, aunt orteacher and identify the types of silksuch as mulberry silk, tassar silk, erisilk, mooga silk, etc. Compare thetexture of these silks with that of theartificial silk pieces, which containsynthetic fibres. Try and collect picturesof different moths whose caterpillarsprovide the various types of silk.Activity 3.6Take an artificial (synthetic) silk threadand a pure silk thread. Burn thesethreads carefully. Did you notice anydifference in the smell while burning?Now, burn a woollen fibre carefully.Did it smell like burning of artificialsilk or that of pure silk? Can youexplain why?To remember when the cocoon stageis reached in the life history of the silkmoth, try the following activity.Activity 3.7Photocopy Fig. 3.9. Cut out pictures ofthe stages of the life history of the silkmoth, and paste them on pieces ofcardboard or chart paper. Jumblethem. Now try and arrange the stagesin the correct sequence. Whoever doesit fastest wins.You may also describe the life historyin your own words. Write it down in yourscrap book.In India, women are significantly involved in various kinds of industries relatedto silk production. These are rearing of silkworms, reeling of silk from cocoonsand processing of raw silk into fabrics. By their enterprise, they contribute tothe nation’s economy. China leads the world in silk production. India also ranksamong the leading silk producing countries.FIBRETO FABRIC2929

www.GOALias.blogspot.comFrom cocoon to silkFor obtaining silk, moths are rearedand their cocoons are collected to getsilk threads.Rearing silkworms: A female silk mothlays hundreds of eggs at a time[Fig. 3.10 (a)]. The eggs are storedcarefully on strips of cloth or paper andsold to silkworm farmers. The farmerskeep eggs under hygienic conditionsand under suitable conditions oftemperature and humidity.The eggs are warmed to a suitabletemperature for the larvae to hatch fromeggs. This is done when mulberry trees[Fig. 3.10 (b)] bear a fresh crop of leaves.The larvae, called caterpillars orsilkworms, eat day and night andincrease enormously in size [Fig. 3.10 (c)].(a) Female silkwormmoth with eggsLeaf of Mulberry(b) Mulberry tree(c) Larva (Caterpillar/Silkworm) feeding onmulberry leavesFig. 3.10 Rearing silkworms(d) CocoonsDiscovery of silkThe exact time of discovery of silk is perhaps unknown. According to an oldChinese legend, the empress Si-lung-Chi was asked by the emperor Huang-ti tofind the cause of the damaged leaves of mulberry trees growing in their garden.The empress found white worms eating up mulberry leaves. She also noticedthat they were spinning shiny cocoons around them. Accidentally a cocoondropped into her cup of tea and a tangle of delicate threads separated from thecocoon. Silk industry began in China and was kept a closely guarded secret forhundreds of years. Later on, traders and travellers introduced silk to othercountries. The route they travelled is still called the ‘silk route’.30SCIENCE

www.GOALias.blogspot.comThe worms are kept in clean bambootrays along with freshly choppedmulberry leaves. After 25 to 30 days,the caterpillars stop eating andmove to a tiny chamber of bamboo inthe tray to spin cocoons [Fig. 3.10 (d)].Small racks or twigs may be providedin the trays to which cocoons getattached. The caterpillar or silkwormspins the cocoon inside which developsthe silk moth.Processing silk: A pile of cocoons isused for obtaining silk fibres. Thecocoons are kept under the sun or boiledor exposed to steam. The silk fibresPaheli wants to know if thecotton thread and silk threadare spun and woven in thesame manner.separate out. The process of taking outthreads from the cocoon for use as silkis called reeling the silk. Reeling is donein special machines, which unwindthe threads or fibres of silk from thecocoon. Silk fibres are then spun intosilk threads, which are woven into silkcloth by weavers.KeywordsCocoonFleeceReelingScouringSericultureShearingSilk mothSilkwormSortingWhat you have learnt• Silk comes from silkworms and wool from sheep, goat and yak. Hencesilk and wool are animal fibres.• The hairs of camel, llama and alpaca are also processed to yield wool.• In India, mostly sheep are reared for getting wool.• Sheep hair is sheared off from the body, scoured, sorted, dried, dyed,spun and woven to yield wool.• Silkworms are caterpillars of silk moth.• During their life cycle, the worms spin cocoons of silk fibres.• Silk fibres are made of a protein.• Silk fibres from cocoons are taken out and reeled into silk threads.• Weavers weave silk threads into silk cloth.FIBRETO FABRIC3131

www.GOALias.blogspot.comExercises1. You must be familiar with the following nursery rhymes:(i) ‘Baa baa black sheep, have you any wool.’(ii) ‘Mary had a little lamb, whose fleece was white as snow.’Answer the following:(a)(b)Which parts of the black sheep have wool?What is meant by the white fleece of the lamb?2. The silkworm is (a) a caterpillar, (b) a larva. Choose the correct option.(i) a (ii) b (iii) both a and b (iv) neither a nor b.3. Which of the following does not yield wool?(i) Yak (ii) Camel (iii) Goat (iv) Woolly dog4. What is meant by the following terms?(i) Rearing (ii) Shearing (iii) Sericulture5. Given below is a sequence of steps in the processing of wool. Which arethe missing steps? Add them.Shearing, __________, sorting, __________,__________.6. Make sketches of the two stages in the life history of the silk moth whichare directly related to the production of silk.7. Out of the following, which are the two terms related to silk production?Sericulture, floriculture, moriculture, apiculture and silviculture.Hints: (i) Silk production involves cultivation of mulberry leaves andrearing silkworms.(ii)Scientific name of mulberry is Morus alba.8. Match the words of Column I with those given in Column II:Column IColumn II1. Scouring (a) Yields silk fibres2. Mulberry leaves (b) Wool yielding animal3. Yak (c) Food of silk worm4. Cocoon (d) Reeling(e)Cleaning sheared skin32SCIENCE

www.GOALias.blogspot.com9. Given below is a crossword puzzle based on this lesson. Use hints to fillin the blank spaces with letters that complete the words.DownAcross(D) 1 : Thorough washing (A) 1 : Keeps warm2 : Animal fibre 2 : Its leaves are eaten by silkworms3 : Long thread like structure 3 : Hatches from egg of mothExtended Learning — Activities and Projects1.Paheli wants to know themaximum length ofcontinuous silk thread thatcan be obtained from a cocoon.Find out for her.2.Boojho wants to know whycaterpillars need to shed their skinwhen they grow bigger but wehumans do not.Do you have any idea?FIBRETO FABRIC3333

www.GOALias.blogspot.com3.Boojho wants to know whycaterpillars should not be collectedwith bare hands.Can you help him?4. Paheli wanted to buy a silk frock and went to the market with her mother.There they found that the artificial (synthetic) silk was much cheaperand wanted to know why. Do you know why? Find out.5. Someone told Paheli that an animal called ‘Vicuna’ also gives wool. Canyou tell her where this animal is found? Look for this in a dictionary oran encyclopaedia.6. When handloom and textile exhibitions are held, certain stalls displayreal moths of various varieties of silk and their life histories. Try andvisit these stalls with elders or teachers and see these moths and stagesof their life history.7. Look for eggs of any moth or butterfly in your garden or park or anyother place full of plants. They look like tiny specks (dots) laid in acluster on the leaves. Pull out the leaves containing eggs and placethem in a cardboard box. Take some leaves of the same plant or anotherplant of the same variety, chop them and put them in the box. Eggs willhatch into caterpillars, which are busy eating day and night. Add leaveseveryday for them to feed upon. Sometimes you may be able to collectthe caterpillars. But be careful. Use a paper napkin or a paper to holda caterpillar.Observe everyday. Note the (i) number of days taken for eggs to hatch,(ii) number of days taken to reach the cocoon stage, and (iii) number ofdays to complete life cycle. Record your observations in your notebook.You can read more on the following website:www.indiansilk.kar.nic.in/Did you know?In terms of the number of sheep, India ranks third in the world, behindChina and Australia. However, the New Zealand sheep are known to yieldthe best wool.34SCIENCE

www.GOALias.blogspot.com4HeatIn Chapter 3 you learnt that woollenclothes are made from animal fibres.You also know that cotton clothesare made from plant fibres. We wearwoollen clothes during winters when itis cold outside. Woollen clothes keep uswarm. We prefer to wear light colouredcotton clothes when it is hot. These giveus a feeling of coolness. You might havewondered why particular types ofclothes are suitable for a particularseason.In winter you feel cold inside thehouse. If you come out in the sun, youfeel warm. In summer, you feel hot eveninside the house. How do we knowwhether an object is hot or cold? Howdo we find out how hot or cold an objectis? In this chapter we shall try to seekanswers to some of these question.4.1 HOTAND COLDIn our day-to-day life, we come across anumber of objects. Some of them are hotTable 4.1: Hot and cold objectsObjectIce creamCold/Coolool√Warm/Hototand some of them are cold. Tea is hotand ice is cold. List some objects youuse commonly in Table 4.1. Mark theseobjects as hot or cold.Do not touch objects which are toohot. Be careful while handling acandle flame or a stove.We see that some objects are coldwhile some are hot. You also know thatsome objects are hotter than otherswhile some are colder than others. Howdo we decide which object is hotter thanthe other? We often do it by touchingthe objects. But is our sense of touchreliable? Let us find out.Activity 4.1Take three large mugs. Label them asA, B and C. Put cold water in mug Aand hot water in mug B. Mix some coldMake sure that water is not so hot thatyou burn your hand(A) (B) (C)Spoon in atea cupFruit juiceHandle of afrying pan Fig. 4.1 Feeling water in three mugs

www.GOALias.blogspot.comand hot water in mug C. Now dip yourleft hand in mug A and the right handin mug B. After keeping the hands inthe two mugs for 2–3 minutes, put boththe hands simultaneously in mug C(Fig. 4.1). Do both the hands get thesame feeling?Boojho’s confusion shows that wecannot always rely on our sense of touchto decide whether an objectis hot or cold. Sometimesit may deceive us.Then, how do we findout how hot an object reallyis? A reliable measure of thehotness of an object is itstemperature. Temperature ismeasured by a device calledthermometer.4.2Boojho says,“My left handtells me that the water in mugC is hot and the right handtells me that the same wateris cold. What should Iconclude?”4.2 MEASURINGTEMPERATUREHave you seen a thermometer? Recallthat when you or someone else in yourfamily had fever, the temperature wasmeasured by a thermometer. Thethermometer that measures our bodytemperature is called a clinicalthermometer. Hold the thermometer inFig. 4.2 A clinical thermometeryour hand and examine it carefully. Ifyou do not have a thermometer, requesta friend to share it with you. A clinicalthermometer looks like the one shownin Fig. 4.2.A clinical thermometer consists of along, narrow, uniform glass tube. It hasa bulb at one end. This bulb containsmercury. Outside the bulb, a smallshining thread of mercury can be seen.If you do not see the mercury thread,rotate the thermometer a bit till you seeit. You will also find a scale on thethermometer. The scale we use is thecelsius scale, indicated by °C.Boojho wondered which of the two scalesshown in Fig. 4.2 he should read. Paheli toldhim that India has adopted the celsius scaleand we should read that scale. The other scalewith the range 94–108 degrees is theFahrenheit scale (°F). It was in use earlier.A clinical thermometer readstemperature from 35°C to 42°C.Activity 4.2Reading a thermometerLet us learn how to read a thermometer.First, note the temperature differenceindicated between the two bigger marks.Also note down the number of divisions36SCIENCE

www.GOALias.blogspot.comPrecautions to be observed while reading a clinical thermometer• Thermometer should be washed before and after use, preferably with anantiseptic solution.• Ensure that before use the mercury level is below 35°C.• Read the thermometer keeping the level of mercury along the line of sight.(See Fig. 4.3).• Handle the thermometer with care. If it hits against some hard object, it canbreak.• Don’t hold the thermometer by the bulb while reading it.(shown by smaller marks) between thesemarks. Suppose the bigger marks readone degree and there are five divisionsbetween them. Then, one small divisioncan read 1 0.2 C .5Wash the thermometer, preferablywith an antiseptic solution. Hold itfirmly and give it a few jerks. The jerkswill bring the level of mercury down.Ensure that it falls below 35°C. Nowplace the bulb of the thermometerunder your tongue. After one minute,take the thermometer out and note thereading. This is your body temperature.The temperature should always bestated with its unit, °C.What did you record as your bodytemperature?The normal temperature of humanbody is 37°C. Note that the temperatureis stated with its unit.Paheli measured her bodytemperature. She got worried asit was not exactly 37°C.Let us try to assure Paheli that thereis nothing wrong with her.Activity 4.3Measure the body temperature of someof your friends (at least 10) with aTable 4.2: Body temperature ofsome personsNameTemperature (°C)Fig. 4.3 Correct method of reading a clinicalthermometerHEAT3737

www.GOALias.blogspot.comclinical thermometer. Record yourobservations as in Table 4.2.Is the body temperature of everyperson 37°C?The temperature of every person maynot be 37°C. It could be slightly higheror slightly lower. Actually, what we callnormal temperature is the average bodytemperature of a large number of healthypersons.The clinical thermometer is designedto measure the temperature of humanbody only. The temperature of humanbody normally does not go below 35 o Cor above 42 o C. That is the reasonthat this thermometer has the range35 o C to 42 o C.Boojho got a naughty idea. Hewanted to measure the temperatureof hot milk using a clinicalthermometer. Paheli stopped himfrom doing so.CAUTIONDo not use a clinical thermometer formeasuring the temperature of anyobject other than the human body.Also avoid keeping the thermometer inthe sun or near a flame. It may break.4.3 L4.3 LABORATORYTHERMOMETERHow do we measure the temperature ofother objects? For this purpose, thereare other thermometers. One suchthermometer is known as the laboratorythermometer. The teacher will show youDifferent types of thermometersare used for different purposes.The maximum and minimumtemperatures of the previousday, reported in weatherreports, are measured bya thermometer called themaximum-minimumthermometer.this thermometer. Look at itcarefully and note the highest andthe lowest temperature it canmeasure. The range of alaboratory thermometer isgenerally from –10°C to 110°C(Fig. 4.4). Also, as you did in thecase of the clinical thermometer,find out how much a smalldivision on this thermometerreads. You would need thisinformation to read thethermometer correctly.Let us now learn how thisthermometer is used.Activity 4.4Take some tap water in a beakeror a mug. Dip the thermometerin water so that the bulb isimmersed in water but does nottouch the bottom or the sides ofthe container. Hold thethermometer vertically (Fig. 4.5).Observe the movement of mercuryin the thermometer. Wait till themercury thread becomes steady.Fig. 4.4 A laboratory thermometer38SCIENCE

www.GOALias.blogspot.comIn addition to the precautions needed while reading a clinicalthermometer, the laboratory thermometer• should be kept upright not tilted. (Fig. 4.5)• bulb should be surrounded from all sides by the substance of which thetemperature is to be measured. The bulb should not touch the surface of thecontainer.Fig. 4.5 Measuring temperature of water withan laboratory thermometerNote the reading. This is the temperatureof water at that time.Compare the temperature of waterrecorded by each student in the class.Are there any variations in thereadings? Discuss the possible reasons.Let us try to answer this question.Activity 4.5Take some hot water in a beaker or amug. Dip the thermometer in water.Wait till the mercury thread becomessteady and note the temperature. Nowtake out the thermometer from water.Observe carefully what happens now.Do you notice that as soon as you takethe thermometer out of water, the levelof mercury begins to fall. This meansthat the temperature must be read whilethe thermometer is in water.You may recall that while taking yourown temperature, you have to take thethermometer out of your mouth to notethe reading. Can you then use thelaboratory thermometer to measure yourBoojho now understand whyclinical thermometer cannot beused to measure hightemperatures. But still wonderswhether a laboratory thermometercan be used to measure his bodytemperature.Boojho wonders why the levelof mercury should change atall when the bulb of thethermometer is brought in contactwith another object?HEAT3939

www.GOALias.blogspot.combody temperature? Obviously, it is notconvenient to use the laboratorythermometer for this purpose.Why does the mercury not fall or risein a clinical thermometer when takenout of the mouth?Observe a clinical thermometeragain. Do you see a kink near the bulb(Fig. 4.6).What is the use of the kink? Itprevents mercury level from falling onits own.Fig. 4.6 A clinical thermometer has a kink in itThere is a lot of concern overthe use of mercury inthermometers. Mercury is atoxic substance and is verydifficult to dispose of if athermometer breaks. Thesedays, digital thermometersare available which do notuse mercury.4.4 T4.4 TRANSFEROF HEATYou might have observed that a fryingpan becomes hot when kept on a flame.It is because the heat passes from theflame to the utensil. When the pan isremoved from the fire, it slowly coolsdown. Why does it cool down? The heatis transferred from the pan to thesurroundings. So you can understandthat in both cases, the heat flows froma hotter object to a colder object. In fact,Paheli asks: “Does it meanthat heat will not betransferred if the temperature oftwo objects is the same?”in all cases heat flows from a hotterobject to a colder object.How does heat flow? Let usinvestigate.Activity 4.6Take a rod or flat strip of a metal, say ofaluminium or iron. Fix a few small waxpieces on the rod. These pieces shouldbe at nearly equal distances (Fig. 4.7).Clamp the rod to a stand. If you do notfind a stand, you can put one end ofthe rod in between bricks. Now, heatthe other end of the rod and observe.What happens to the wax pieces? Dothese pieces begin to fall? Which piecefalls the first? Do you think that heat isFig. 4.7 Flow of heat through a metal striptransferred from the end nearest to theflame to the other end?The process by which heat istransferred from the hotter end to thecolder end of an object is known asconduction. In solids, generally, the40SCIENCE

www.GOALias.blogspot.comFig. 4.8 Conduction of heat by differentmaterialsheat is transferred by the process ofconduction.Do all substances conduct heateasily? You must have observed thatthe metallic pan for cooking has a plasticor wooden handle. Can you lift a hotpan by holding it from the handlewithout getting hurt?Activity 4.7Heat water in a small pan or a beaker.Collect some articles such as a steelspoon, plastic scale, pencil and divider.Dip one end of each of these articles inhot water (Fig. 4.8). Wait for a fewTable 4.3ArticleMaterial withwhich the articleis made ofSteel spoon Metal Yesminutes. Touch the other end. Enteryour observation in Table 4.3.The materials which allow heat topass through them easily areconductors of heat. For examples,aluminum, iron and copper. Thematerials which do not allow heat topass through them easily are poorconductors of heat such as plastic andwood. Poor conductors are known asinsulators.The water and air are poorconductors of heat. Then, how does theheat transfer take place in thesesubstances? Let us find out.Activity 4.8Take a round bottom flask (if flask isnot available, a beaker can be used). Fillit two-thirds with water. Place it on atripod, or make some arrangement toplace the flask in such a way that youcan heat it by placing a candle below it.Wait till the water in the flask isstill. Place a crystal of potassiumpermanganate at the bottom of the flaskgently using a straw. Now, heat the waterby placing the candle just below thecrystal.Write your observation in yournotebook and also draw a picture ofwhat you observe (Fig. 4.9).When water is heated,the water near the flame getshot. Hot water rises up.The cold water from thesides moves down towardsthe source of heat. Thiswater also gets hot and risesDoes the otherend get hotYes/NoHEAT4141

www.GOALias.blogspot.comFig. 4.10 Transfer of heat by convection in airFig. 4.9 Convection of heat in waterand water from the sides moves down.This process continues till the wholewater gets heated. This mode of heattransfer is known as convection.How does the heat travel in air? Inwhich direction does the smoke go?The air near the heat source gets hotand rises. The air from the sides comesin to take its place. In this way the airgets heated. The following activityconfirms this idea.Activity 4.9Light a candle. Keep one hand above theflame and one hand on the side of theflame (Fig. 4.10). Do your hands feelequally hot? If not which hand feelshotter? And why?Be careful. Keep your hands at a safedistance from the flame so that theydo not get burnt.Notice that towards the top, the airgets heated by convection. Therefore, thehand above the flame feels hot. On thesides, however, there is no convectionand air does not feel as hot as atthe top.The people living in the coastal areasexperience an interesting phenomenon.During the day, the land gets heatedfaster than the water. The air over theland becomes hotter and rises up. Thecooler air from the sea rushes in towardsthe land to take its place. The warm airfrom the land moves towards the sea tocomplete the cycle. The air from the seais called the sea breeze. To receive thecooler sea breeze, the windows of thehouses in coastal areas are made to facethe sea. At night it is exactly the reverse(Fig. 4.11). The water cools down moreslowly than the land. So, the cool airfrom the land moves towards the sea.This is called the land breeze. Fig. 4.11shows this phenomenon.When we come out in the sun, wefeel warm. How does the heat from thesun reach us? It cannot reach us byconduction or convection as there is nomedium such as air in most part of the42SCIENCE

www.GOALias.blogspot.comDay timeNight timeCoolHotHotCoolFig. 4.11 Land breeze and sea breezespace between the earth and the sun.From the sun the heat comes to us byanother process known as radiation.The transfer of heat by radiation doesnot require any medium. It can takeplace whether a medium is present ornot. When we sit in front of a roomheater, we get heat by this process. Ahot utensil kept away from the flamecools down as it transfers heat to thesurroundings by radiation. Our bodytoo, gives heat to the surroundings andreceives heat from it by radiation.All hot bodies radiate heat. Whenthis heat falls on some object, a part ofit is reflected, a part is absorbed and apart may be transmitted. Thetemperature of the object increases dueto the absorbed part of the heat. Whyare you advised to use an umbrella whenyou go out in the sun?4.54.5 KINDSOF CLOTHESWE WEARINSUMMERAND WINTERYou know that in summer we preferlight-coloured clothes and in winter weusually wear dark-coloured clothes. Whyis it so? Let us find outActivity 4.10Take two identical tin cans. Paint theouter surface of one black and of theother white (Fig. 4.12). Pour equalamounts of water in each and leave themin the mid-day sun for about an hour.Measure the temperature of water inboth the cans. Do you find anydifference in the temperatures? InHEAT4343

www.GOALias.blogspot.comWe often use electricity and fuels like coal and wood to keep our houses cool orwarm. Is it possible to construct buildings, that are not affected much by heatand cold outside? This can be done by constructing outer walls of buildings sothat they have trapped layers of air. One way of doing this is to use hollowbricks, which are available these days.Fig. 4.12 Containers with black and whitesurfacewhich can is the water warmer? Youcan feel the difference even by touchingwater in the two cans.Activity 4.11Fill the two cans used in Activity 10 withthe same amount of hot water at thesame temperature (say, at 60 o C). Leavethe cans in a room or in a shade. Notethe temperature of water after 10–15minutes. Does the temperature of waterin both the cans fall by the sameamount?Do these activities suggest to you thereason why it is more comfortable towear white or light-coloured clothes inthe summer and dark-coloured clothesin the winter? Dark surfaces absorbmore heat and, therefore, we feelcomfortable with dark coloured clothesin the winter. Light coloured clothesreflect most of the heat that falls on themand, therefore, we feel more comfortablewearing them in the summer.Woollen clothes keep us warmin winterIn the winter, we use woollen clothes.Wool is a poor conductor of heat.Moreover, there is air trapped in betweenthe wool fibres. This air prevents the flowof heat from our body to the coldsurroundings. So, we feel warm.Suppose you are given the choice inwinter of using either one thick blanketor two thin blankets joined together.What would you choose and why?Remember that there would be a layerof air in between the blankets.KeywordsCelsius scaleConductionConductorConvectionInsulatorLand breezeRadiationSea breezeTemperatureThermometer44SCIENCE

www.GOALias.blogspot.comWhat you have learnt• Our sense of touch is not always a reliable guide to the degree of hotnessof an object.• Temperature is a measure of the degree of hotness of an object.• Thermometer is a device used for measuring temperatures.• Clinical thermometer is used to measure our body temperature. Therange of this thermometer is from 35°C to 42°C. For other purposes, weuse the laboratory thermometers. The range of these thermometers isusually from –10°C to 110°C.• The normal temperature of the human body is 37°C.• The heat flows from a body at a higher temperature to a body at a lowertemperature. There are three ways in which heat can flow from oneobject to another. These are conduction, convection and radiation.• In solids, generally, the heat is transferred by conduction. In liquidsand gases the heat is transferred by convection. No medium is requiredfor transfer of heat by radiation.• The materials which allow heat to pass through them easily areconductors of heat.• The materials which do not allow heat to pass through them easily arecalled insulators.• Dark-coloured objects absorb radiation better than the light-colouredobjects. That is the reason we feel more comfortable in light-colouredclothes in the summer.• Woollen clothes keep us warm during winter. It is so because wool is apoor conductor of heat and it has air trapped in between the fibres.Exercises1. State similarities and differences between the laboratory thermometerand the clinical thermometer.2. Give two examples each of conductors and insulators of heat.3. Fill in the blanks :(a) The hotness of an object is determined by its __________.(b) Temperature of boiling water cannot be measured by a_____________ thermometer.(c) Temperature is measured in degree ______________.HEAT4545

www.GOALias.blogspot.com(d)(e)No medium is required for transfer of heat by the process of__________.A cold steel spoon is dipped in a cup of hot milk. It transfers heatto its other end by the process of ______________.(f ) Clothes of ______________ colours absorb heat better than clothesof light colours.4. Match the following :(i) Land breeze blows during (a) summer(ii) Sea breeze blows during (b) winter(iii) Dark coloured clothes are preferred during (c) day(iv) Light coloured clothes are preferred during (d) night5. Discuss why wearing more layers of clothing during winter keeps uswarmer than wearing just one thick piece of clothing .6. Look at Fig. 4.13. Mark where the heat is being transferred byconduction, by convection and by radiation.Fig. 4.137. In places of hot climate it is advised that the outer walls of houses bepainted white. Explain.8. One litre of water at 30°C is mixed with one litre of water at 50°C. Thetemperature of the mixture will be(a) 80°C (b) more than 50°C but less than 80°C(c) 20°C (d) between 30°C and 50°C46SCIENCE

www.GOALias.blogspot.com9. An iron ball at 40°C is dropped in a mug containing water at 40°C.The heat will(a) flow from iron ball to water.(b) not flow from iron ball to water or from water to iron ball.(c) flow from water to iron ball.(d) increase the temperature of both.10. A wooden spoon is dipped in a cup of ice cream. Its other end(a) becomes cold by the process of conduction.(b) becomes cold by the process of convection.(c) becomes cold by the process of radiation.(d) does not become cold.11. Stainless steel pans are usually provided with copper bottoms. Thereason for this could be that(a) copper bottom makes the pan more durable.(b) such pans appear colourful.(c) copper is a better conductor of heat than the stainless steel.(d) copper is easier to clean than the stainless steel.Extended Learning — Activities and Projects1. Go to a doctor or your nearest health centre. Observe the doctor takingtemperature of patients. Enquire:(a) why she dips the thermometer in a liquid before use.(b) why the thermometer is kept under the tongue.(c) whether the body temperature can be measured by keeping thethermometer at some place other than the mouth.(d) whether the temperature of different parts of the body is the sameor different.You can add more questions which come to your mind.2. Go to a veterinary doctor (a doctor who treats animals). Discuss andfind out the normal temperature of domestic animals and birds.3. Wrap a thin paper strip tightly around an iron rod. Try to burn thepaper with candle while rotating the iron rod continuously. Does it burn?Explain your observation.HEAT4747

www.GOALias.blogspot.com4. Take a sheet of paper. Draw a spiral on it as shown in the Fig. 4.14. Cut outthe paper along the line. Suspend the paper as shown in Fig. 4.14 abovea lighted candle. Observe what happens. Think of an explanation.Fig. 4.145. Take two similar transparent glass bottles having wide mouths. Put afew crystals of potassium permanganate or pour a few drops of ink inone bottle. Fill this bottle with hot water. Fill the other bottle with coldwater. Cover the cold water bottle with a thick piece of paper such as apostcard. Press the postcard firmly with one hand and hold the bottlewith the other hand. Invert the bottle and place it on top of the hotwater bottle. Hold both the bottles firmly. Ask some other person to pullthe postcard. Observe what happens. Explain.You can read more on the following website:www.bbc.co.uk/schools/gcsebitesize/physics/energy/energytransferrev6.shtmlDid you know?The celsius scale was devised by a Swedish astronomer, Anders Celsiusin 1742. Strangely, he fixed the temperature of the boiling water as 0°Cand of freezing water as 100°C. However, this order was reversed verysoon.48SCIENCE

www.GOALias.blogspot.com5Acids, Bases and SaltsWe use in our daily life a largenumber of substances suchas lemon, tamarind, commonsalt, sugar and vinegar. Do they havethe same taste? Let us recall tastes ofsome edible substances listed inTable 5.1. If you have not tasted any ofthese substances taste it now and enterthe result in Table 5.1.CAUTION1. Do not taste anything unless askedto do so.2. Do not touch anything unless askedto do so.SubstanceLemon juiceOrange juiceVinegarCurdTamarind (imli)SugarCommon saltAmlaBaking sodaGrapesUnripe mangoTable 5.1Taste (sour/bitter/any other)You find that some of thesesubstances taste sour, some taste bitter,some taste sweet and some taste salty.5.1 A5.1 ACIDSAND BASESCurd, lemon juice, orange juice andvinegar taste sour. These substancestaste sour because they contain acids.The chemical nature of suchsubstances is acidic. The word acidcomes from the Latin word acere whichmeans sour. The acids in thesesubstances are natural acids.What about baking soda? Does it alsotaste sour? If not, what is its taste? Since,it does not taste sour it means, that ithas no acids in it. It is bitter in taste. Ifyou rub its solution between fingers, itfeels soapy. Substances like these whichare bitter in taste and feel soapy ontouching are known as bases. The natureof such substances is said to be basic.If we cannot taste every substance,how do we find its nature?Special type of substances are usedto test whether a substance is acidic orbasic. These substances are known asindicators. The indicators change theircolour when added to a solutioncontaining an acidic or a basicsubstance. Turmeric, litmus, china rosepetals (Gudhal), etc., are some of thenaturally occurring indicators.

www.GOALias.blogspot.comName of acidAcetic acidFormic acidCitric acidLactic acidOxalic acidAscorbic acid(Vitamin C)Tartaric acidDo you know?Found inVinegarAnt’s stingCitrus fruits suchas oranges,lemons, etc.CurdSpinachAmla, Citrus fruitsTamarind, grapes,unripe mangoes, etc.All the acids mentionedabove occur in natureName of baseFound inCalcium hydroxideLime waterAmmonium hydroxide Window cleanerSodium hydroxide/ SoapPotassium hydroxideMagnesium hydroxide Milk of magnesia5.25.2 NATURALINDICATORSAROUND USLitmus: A natural dyeThe most commonly used naturalindicator is litmus. It is extractedfrom lichens (Fig. 5.1). It has amauve (purple) colour in distilledwater. When added to an acidicsolution, it turns red and whenadded to a basic solution, it turnsblue. It is available in the form of asolution, or in the form of strips ofpaper, known as litmus paper.Generally, it is available as red andblue litmus paper (Fig. 5.1).(a)Can I taste all substances tofind their taste?No. Have you not read thecaution? We should nottaste unknownsubstances. They couldharm us.(b)Fig. 5.1 (a) Lichens, and (b) Red and bluelitmus paper50SCIENCE

www.GOALias.blogspot.comActivity 5.1• Mix some water with lemon juice in aplastic cup/tumbler/test tube.• Put a drop of the above solution on astrip of the red litmus paper with thehelp of a dropper.Is there any change in colour?• Repeat the same exercise with theblue litmus paper.Note down if there is any change incolour.Perform the same activity with thefollowing substances:Tap water, detergent solution, aerateddrink, soap solution, shampoo, commonsalt solution, sugar solution, vinegar,baking soda solution, milk of magnesia,washing soda solution, lime water. Ifpossible make solutions in distilled water.Record your observations as inTable. 5.2.In your Table, are there anysubstances on which litmus had noeffect? Name those substances.The solutions which do not changethe colour of either red or blue litmusare known as neutral solutions. Thesesubstances are neither acidic nor basic.Fig. 5.2 Children performing litmus testTurmeric is another naturalindicatorActivity 5.2• Take a tablespoonful of turmericpowder. Add a little water and makea paste.• Make turmeric paper by depositingturmeric paste on blotting paper/filterpaper and drying it. Cut thin stripsof the yellow paper obtained.• Put a drop of soap solution on thestrip of turmeric paper.What do you observe?To prepare limewater, dissolve some lime (chuna) in water in a bottle. Stir thesolution and keep it for some time. Pour a little from the top. This is lime water.Table 5.2S. No. Test solutionEffect on redlitmus paperEffect on bluelitmus paperInference, BACIDSCIDS, , BASESAND SALTS5151

www.GOALias.blogspot.comYou can prepare a card for yourmother on her birthday. Applyturmeric paste on a sheet of planewhite paper and dry it. Draw abeautiful flower with soap solutionwith the help of a cotton bud. You willget a beautiful greeting card.Now I understand why aturmeric stain on my white shirtis turned to red when it iswashed with soap. It is becausethe soap solution is basic.AcidIndicatorBaseTurmeric pasteSoapsolutionSimilarly test the solutions listed inTable 5.3 and note down yourobservations. You may try solutions ofother substances also.China Rose as IndicatorActivity 5.3Collect some China rose (Gudhal ) petalsand place them in a beaker. Add someS. No. Test solution1. Lemon juice2. Orange juice3. Vinegar4. Milk of magnesia5. Baking soda6. Lime water7. Sugar8. Common saltTable 5.3Fig. 5.3 China rose flower and indicatorprepared from itEffect on turmeric solutionChinaroseRemarks52SCIENCE

www.GOALias.blogspot.comTable 5.4S. No. Test solution Initial colour1. Shampoo (dilute solution)2. Lemon juice3. Soda water4. Sodium hydrogencarbonate solution5. Vinegar6. Sugar solution7. Common salt solutionFinal colourwarm water. Keep the mixture for sometime till water becomes coloured. Usethe coloured water as an indicator. Addfive drops of the indicator to each of thesolutions given in Table 5.4.What is the effect of the indicator onacidic, basic and neutral solutions?China rose indicator (Fig. 5.3) turnsacidic solutions to dark pink (magenta)and basic solutions to green.I am not getting the same resultwhen using solid baking sodaon dry litmus paper. Why?Make a solution of bakingsoda and then try.Paheli brought the following paheli(riddle) for you.Coffee is brownAnd bitter in taste.Is it an acid?Or a base?Don’t give the answerWithout any test,You are in the darkWith its taste.Activity 5.4The teacher is requested to get thefollowing dilute chemicals from his/herschool laboratory or from a nearbyschool: hydrochloric acid, sulphuricacid, nitric acid, acetic acid, sodiumhydroxide, ammonium hydroxide,calcium hydroxide (lime water).Table 5.5S. Name of acidNo.Effect onlitmus paperEffect onturmeric paperEffect onChina rosesolution1. Dilute hydrochloric acid2.3., BACIDSCIDS, , BASESAND SALTS5353

www.GOALias.blogspot.comAre you familiar with the term acid rain? Have you ever heard about damagingeffect of acid rain? As the name indicates the rain containing excess of acids iscalled an acid rain. Where do these acids come from? The rain becomes acidicbecause carbon dioxide, sulphur dioxide and nitrogen dioxide (which are releasedinto the air as pollutants) dissolve in rain drops to form carbonic acid, sulphuricacid and nitric acid respectively. Acid rain can cause damage to buildings,historical monuments, plants and animals.CAUTIONGreat care should be taken whilehandling laboratory acids and basesbecause these are corrosive in nature,irritating and harmful to skin.Demonstrate the effect of the threeindicators on each of these solutions.Record your observations in Table 5.5.5.3 NEUTRALISATIONWe have learnt that acids turn bluelitmus red and bases turn red litmusblue. Let us see what happens when anacid is mixed with a base.We are going to use an indicator youhave not used so far. It is calledphenolphthalein.Activity 5.5To be demonstrated by the teacher inthe classFill one fourth of a test tube with dilutehydrochloric acid. Note down its colour.Note down the colour of phenolphthaleinsolution also. Add 2–3 drops of theindicator to the acid. Now shake the testtube gently. Do you observe any changein colour of the acid?Add to the acidic solution a drop ofsodium hydroxide solution by a dropper.Stir the tube gently. Is there any changein the colour of the solution? Continueadding the sodium hydroxide solutiondrop by drop while stirring till the pinkcolour just appears.Now add one more drop of dilutehydrochloric acid. What do you observe?The solution again becomes colourless.Again add one drop of sodiumhydroxide solution. Is there any changein colour? The solution again becomespink in colour.It is evident that when the solutionis basic, phenolphthalein gives a pinkcolour. On the other hand, when thesolution is acidic, it remains colourless.BaseAcid + IndicatorFig. 5.4 Process of neutralisation54SCIENCE

www.GOALias.blogspot.comWhen an acidic solution is mixedwith a basic solution, both the solutionsneutralise the effect of each other. Whenan acid solution and a base solution aremixed in suitable amounts, both theacidic nature of the acid and the basicnature of the base are destroyed. Theresulting solution is neither acidic norbasic. Touch the test tube immediatelyafter neutralisation. What do youobserve? In neutralisation reaction, heatis always produced, or evolved. Theevolved heat raises the temperature ofthe reaction mixture.In neutralisation reaction a newsubstance is formed. This is called salt.Salt may be acidic, basic or neutral innature. Thus, neutralisation can bedefined as follows:The reaction between an acid andalt+Watera base is known as neutralisation. Saltand water are produced in this processwith the evolution of heat.Acid+Base Salt+Water(Heat is evolved)The following reaction is an example:Hydrochloric acid (HCl) + Sodiumhydroxide (NaOH)Sodium chloride (NaCl) + Water (H 2O)Boojho added dilute sulphuric acidto lime water. Will the reaction mixturebecome hot or cool?5.4 NEUTRALISATIONSIN EVERYDAYLIFEIndigestionOur stomach contains hydrochloricacid. It helps us to digest food, as youhave learnt in Chapter 2. But toomuch of acid in the stomach causesindigestion. Sometimes indigestionis painful. To relieve indigestion, wetake an antacid such as milk ofmagnesia, which contains magnesiumhydroxide. It neutralises the effect ofexcessive acid.Ant stingThe sting of an ant contains formicacid. When an ant bites, it injectsthe acidic liquid into the skin. Theeffect of the sting can be neutralised byrubbing moist baking soda (sodiumhydrogen carbonate) or calaminesolution, which contains zinccarbonate.Soil treatmentExcessive use of chemical fertilisersmakes the soil acidic. Plants do not growwell when the soil is either too acidic ortoo basic. When the soil is too acidic, itis treated with bases like quick lime(calcium oxide) or slaked lime (calciumhydroxide). If the soil is basic, organicmatter is added to it. Organic matterreleases acids which neutralises thebasic nature of the soil.Factory wastesThe wastes of many factoriescontain acids. If they are allowed toflow into the water bodies, the acidswill kill fish and other organisms.The factory wastes are, therefore,neutralised by adding basicsubstances., BACIDSCIDS, , BASESAND SALTS5555

www.GOALias.blogspot.comKeywordsAcidAcidicBaseWhat you have learntBasicIndicatorNeutralNeutralisationSalt• Acids are sour in taste. Bases are bitter in taste and soapy to touch.• Acid turns blue litmus red. Bases turn red litmus blue.• Substances which are neither acidic nor basic are called neutral.• Solutions of substances that show different colour in acidic, basic andneutral solutions are called indicators.• An acid and a base neutralise each other and form a salt. A salt may beacidic, basic or neutral in nature.Exercises1. State differences between acids and bases.2. Ammonia is found in many household products, such as windowcleaners. It turns red litmus blue. What is its nature?3. Name the source from which litmus solution is obtained. What is theuse of this solution?4. Is the distilled water acidic/basic/neutral? How would you verify it?5. Describe the process of neutralisation with the help of an example.6. Mark ‘T’ if the statement is true and ‘F’ if it is false:(i) Nitric acid turn red litmus blue. (T/F)(ii) Sodium hydroxide turns blue litmus red. (T/F)(iii) Sodium hydroxide and hydrochloric acid neutralise each other andform salt and water. (T/F)(iv) Indicator is a substance which shows different colours in acidicand basic solutions. (T/F)(v) Tooth decay is caused by the presence of a base. (T/F)7. Dorji has a few bottles of soft drink in his restaurant. But, unfortunately,these are not labelled. He has to serve the drinks on the demandof customers. One customer wants acidic drink, another wants basicand third one wants neutral drink. How will Dorji decide which drink isto be served to whom?8. Explain why:(a)An antacid tablet is taken when you suffer from acidity.56SCIENCE

www.GOALias.blogspot.com(b)(c)Calamine solution is applied on the skin when an ant bites.Factory waste is neutralised before disposing it into the waterbodies.9. Three liquids are given to you. One is hydrochloric acid, another issodium hydroxide and third is a sugar solution. How will you identifythem? You have only turmeric indicator.10. Blue litmus paper is dipped in a solution. It remains blue. What is thenature of the solution? Explain.11. Consider the following statements:(a) Both acids and bases change colour of all indicators.(b) If an indicator gives a colour change with an acid, it does not give achange with a base.(c) If an indicator changes colour with a base, it does not change colourwith an acid.(d) Change of colour in an acid and a base depends on the type of theindicator.Which of these statements are correct?(i) All four (ii) a and d (iii) b and c (iv) only dExtended Learning — Activities and Projects1. Using the knowledge of acids and bases, write a secret message withthe help of baking soda and beet root. Explain how it works.(Hint:Prepare baking soda solution in water. Use this solution to writethe message on a sheet of white paper with a cotton bud. Rub a slice offresh beet root over the message.)2. Prepare red cabbage juice by boiling a piece of red cabbage in water.Use it as an indicator and test the acidic and basic solutions with it.Present your observations in the form of a table.3. Bring the soil sample of your area, find out if it is acidic, basic orneutral. Discuss with farmers if they treat the soil in any manner.4. Visit a doctor. Find out the medicines, he prescribes to treat acidity.Ask him how acidity can be prevented.Did you know?Each cell in our body contains an acid, the deoxyribonucleic acid orDNA. It controls every feature of the body such as our looks, colour ofour eyes, our height etc. Proteins that build part of our cells are alsomade of amino acids. The fats in our body contain fatty acids., BACIDSCIDS, , BASESAND SALTS5757

www.GOALias.blogspot.com6Physical and ChemicalChangesEvery day you come across manychanges in your surroundings.These changes may involve oneor more substances. For example, yourmother may ask you to dissolve sugarin water to make a cold drink. Making asugar solution is a change. Similarly,setting curd from milk is a change.Sometimes milk becomes sour. Souringof milk is a change. Stretched rubberband also represents a change.Make a list of ten changes you havenoticed around you.In this chapter we shall perform someactivities and study the nature of thesechanges. Broadly, these changes are oftwo kinds, physical and chemical.Fig. 6.1 Paper pieces6.1 P6.1 PHYSICALCHANGESActivity 6.1Cut a piece of paper in four squarepieces. Cut each square piece furtherinto four square pieces. Lay these pieceson the floor or a table so that the piecesacquire the shape of the original pieceof paper (Fig. 6.1).Obviously, you cannot join the piecesback to make the original piece, but isthere a change in the property of thepaper?Activity 6.2Collect the chalk dust lying on the floornear the blackboard in your classroom.Or, crush a small piece of chalk intodust. Add a little water to the dust tomake a paste. Roll it into the shape of apiece of chalk. Let it dry.Did you recover chalk from thedust?Activity 6.3Take some ice in a glass or plastictumbler. Melt a small portion of ice byplacing the tumbler in the sun. You havenow a mixture of ice and water. Nowplace the tumbler in a freezing mixture(ice plus common salt).Does the water become solid ice onceagain?58SCIENCE

www.GOALias.blogspot.comActivity 6.4Boil some water in a container. Do yousee the steam rising from the surface ofwater? Hold an inverted pan by itshandle over the steam at some distancefrom the boiling water. Observe theinner surface of the pan.Do you see any droplet of waterthere?Activity 6.5CAUTIONBe careful while handling a flame.Hold a used hack-saw blade with apair of tongs. Keep the tip of the freeend on the flame of a gas stove. Wait fora few minutes.Does the colour of the tip of the bladechange?Remove the blade from the flame.Observe the tip once again after sometime.Does it get back its original colour?In Activities 6.1 and 6.2 above, yousaw that paper and a piece of chalkunderwent changes in size. In Activities6.3 and 6.4, water changed its state (fromsolid to liquid, or from gas to liquid). InActivity 6.5, the hack-saw bladechanged colour on heating.Properties such as shape, size, colourand state of a substance are called itsphysical properties. A change in whicha substance undergoes a change in itsphysical properties is called a physicalchange. A physical change is generallyreversible. In such a change no newsubstance is formed.Let us now consider the other kindof change.6.2 CHEMICALCHANGEA change with which you are quitefamiliar is the rusting of iron. If youleave a piece of iron in the open for sometime, it acquires a film of brownishsubstance. This substance is called rustand the process is called rusting(Fig. 6.2). Iron gates of parks orfarmlands, iron benches kept in lawnsand gardens, almost every article of iron,kept in the open gets rusted. At homeyou must have seen shovels and spadesgetting rusted when exposed to theFig. 6.2 Rusting ironPHYSICALAND CHEMICALCHANGES5959

www.GOALias.blogspot.comatmosphere for some time. In thekitchen, a wet iron pan (tawa) often getsrusted if left in that state for some time.Rust is not iron. It is different from ironon which it gets deposited.Let us consider a few more changeswhere new substances are formed.Activity 6.6(To be demonstrated by the teacher)CAUTIONIt is dangerous to look for long at theburning magnesium ribbon. Theteachers should advise children notto stare at the burning ribbon.Get a small piece of a thin strip orribbon of magnesium. Clean its tip withsandpaper. Bring the tip near a candleflame. It burns with a brilliant whiteFig. 6.3 Magnesium ribbon burninglight (Fig. 6.3). When it is completelyburnt it leaves behind a powdery ash.Does the ash look like themagnesium ribbon?The change can be represented bythe following equation:Magnesium (Mg) + Oxygen (O 2) →Magnesium oxide (MgO)The equations here are different fromthose in mathematics. In equationsof this kind, the arrow implies‘becomes’. No attempt should be madeto balance chemical equations at thisstage.Collect the ash and mix it with asmall amount of water. Stir the mixture(aqueous solution) well. Test the mixturewith blue and red litmus papers.Does the mixture turn red litmusblue?Does the mixture turn blue litmusred?On the basis of this test, how do youclassify the aqueous solution — acidicor basic?On dissolving the ash in water itforms a new substance. This change canbe written in the form of the followingequation:Magnesium oxide (MgO) + Water(H 2O) → Magnesium hydroxide [Mg(OH) 2]As you have already learnt inChapter 5, magnesium hydroxide is a base.So, magnesium oxide is a new substanceformed on burning of magnesium.Magnesium hydroxide is another new60SCIENCE

www.GOALias.blogspot.comsubstance formed by mixing magnesiumoxide with water.Activity 6.7(To be demonstrated by the teacher)Dissolve about a teaspoonful of coppersulphate (blue vitriol or neela thotha) inabout half a cup of water in a glasstumbler or a beaker. Add a few drops ofdilute sulphuric acid to the solution.You should get a blue coloured solution.Save a small sample of the solution in atest tube or a small glass bottle. Drop anail or a used shaving blade into theremaining solution. Wait for half anhour or so. Observe the colour of thesolution. Compare it with the colour ofthe sample solution saved separately(Fig. 6.4).colour of the solution from blue togreen is due to the formation of ironsulphate, a new substance. The browndeposit on the iron nail is copper,another new substance. We can writethe reaction as:Copper Sulphate solution (blue) + Iron→ Iron Sulphate solution (green)+ Copper (brown deposit)Activity 6.8Take about a teaspoonful of vinegar ina test tube. Add a pinch of baking sodato it. You would hear a hissing soundand see bubbles of a gas coming out.Pass this gas through freshly preparedlime water as shown in Fig. 6.5.What happens to the lime water?CoppersulphateFig. 6.4 Change in colour of the copper sulphatesolution due to reaction with ironDo you see any change in the colourof the solution?Take out the nail or the blade.Has it changed in any way?The changes that you notice aredue to a reaction between coppersulphate and iron. The change ofThe change in the test tube is asfollows:Vinegar (Acetic acid) + Baking soda(Sodium hydrogencarbonate) →Carbon dioxide + other substancesThe reaction between carbon dioxideand lime water is as follows:PHYSICALAND CHEMICALCHANGES6161

www.GOALias.blogspot.comCarbondioxideVinegar +Baking sodaLimewaterFig. 6.5 Set up to pass gas through lime waterCarbon dioxide (CO 2) + Lime water[Ca(OH) 2] → Calcium Carbonate(CaCO 3) + Water (H 2O)When carbon dioxide is passedthrough lime water, calcium carbonateis formed, which makes lime water milky.The turning of lime water into milky is astandard test of carbon dioxide. You willuse it in Chapter 10 to show that the airwe breathe out is rich in carbon dioxide.In Activities 6.6–6.8, you saw thatin each change one or more newsubstances were formed. In Activity 6.6,the ash was the new substance formedwhen magnesium was burnt. In Activity 6.7,the reaction of copper sulphate with ironproduced iron sulphate and copper.Both of these are new substances.Copper was deposited on the shavingblade of iron. In Activity 6.8, vinegar andbaking soda together produced carbondioxide, which turned lime water milky.Can you name the new substanceformed in this reaction?A change in which one or morenew substances are formed is called achemical change. A chemical changeis also called a chemical reaction.Chemical changes are very importantin our lives. All new substances areformed as a result of chemical changes.For example, if a metal is to be extractedfrom an ore, such as iron from iron ore,we need to carry out a series of chemicalchanges. A medicine is the end productof a chain of chemical reactions. Usefulnew materials, such as plastics anddetergents, are produced by chemicalreactions. Indeed, every new materialis discovered by studying chemicalchanges.We have seen that one or more newsubstances are produce in a chemicalchange. In addition to new products,the following may accompany a chemicalchange:• Heat, light or any other radiation(ultraviolet, for example) may be givenoff or absorbed.• Sound may be produced.• A change in smell may take place ora new smell may be given off.• A colour change may take place .• A gas may be formed.Let us look at some examples.You saw that burning of magnesiumribbon is a chemical change. Burningof coal, wood or leaves is also a chemicalchange. In fact, burning of anysubstance is a chemical change.Burning is always accompanied byproduction of heat.62SCIENCE

www.GOALias.blogspot.comExplosion of a firework is a chemicalchange. You know that such anexplosion produces heat, light, soundand unpleasant gases that pollute theatmosphere. That is why you are advisednot to play with fireworks.When food gets spoiled, it producesa foul smell. Shall we call this change achemical change?You must have noticed that a slice ofan apple acquires a brown colour if it isnot consumed immediately. If you havenot seen this change in colour, cut afresh slice of apple and keep it away forsome time. Repeat the same activity witha slice of potato or brinjal. The changeof colour in these cases is due to theformation of new substances. Are notthese changes chemical changes?In Chapter 5, you neutralised an acidwith a base. Is neutralisation a chemicalchange?A protective shieldYou must have heard of the ozone layerin our atmosphere. It protects us fromthe harmful ultraviolet radiation whichcome from the sun. Ozone absorbs thisradiation and breaks down to oxygen.Oxygen is different from ozone. Canwe call the breaking down of ozone achemical change?If ultraviolet radiation were notabsorbed by ozone, it would reach theearth’s surface and cause harm to usand other life forms. Ozone acts as anatural shield against this radiation.We learnt in Chapter 1 thatplants produce their food bya process called photosynthesis.Can we call photosynthesisa chemical change?Paheli said that even digestionis a chemical change.6.3 R6.3 RUSTINGOF IRONLet us get back to rusting. This is onechange that affects iron articles andslowly destroys them. Since iron is usedin making bridges, ships, cars, truckbodies and many other articles, themonetary loss due to rusting is huge.The process of rusting can berepresented by the following equation:Iron (Fe) + Oxygen (O 2, from the air)+ water (H 2O) → rust (iron oxide Fe 2O 3)For rusting, the presence of bothoxygen and water (or water vapour)is essential.In fact, if the content of moisture inair is high, which means if it is morehumid, rusting becomes faster.So, how do we prevent rusting?Prevent iron articles from coming incontact with oxygen, or water, or both.One simple way is to apply a coat ofpaint or grease. In fact, these coatsshould be applied regularly to preventrusting. Another way is to deposit a layerof a metal like chromium or zinc on iron.PHYSICALAND CHEMICALCHANGES6363

www.GOALias.blogspot.comOh, that is why my friendRita is always complainingabout iron articles rusting sofast. She lives near the coast.This process of depositing a layer of zincon iron is called galvanisation. The ironpipes we use in our homes to carry waterare galvanised to prevent rusting.You know that ships are made of ironand a part of them remains under water.On the part above water also waterdrops keep clinging to the ship’s outersurface. Moreover, the water of the seacontains many salts. The salt watermakes the process of rust formationfaster. Therefore, ships suffer a lot ofdamage from rusting in spite of beingStainless steel is made by mixing ironwith carbon and metals likechromium, nickel and manganese. Itdoes not rust.painted. So much so, that a fraction ofship’s iron has to be replaced every year.Can you imagine the monetary loss tothe world?6.4 CRYSTALLISATIONIn Class VI you have learnt that salt canbe obtained by the evaporation of seawater. The salt obtained in this manneris not pure and its crystals are small.The shape of the crystals cannot be seenclearly. However, large crystals of puresubstances can be formed from theirsolutions. The process is calledcrystallisation. It is an example of aphysical change.Activity 6.9(To be performed in the presence ofthe teacher)CAUTIONUse only dilute sulphuric acid. Becareful while boiling water.Take a cupful of water in a beakerand add a few drops of dilute sulphuricacid. Heat the water. When it startsboiling add copper sulphate powderslowly while stirring continuously(Fig. 6.6). Continue adding coppersulphate powder till no more powder canbe dissolved. Filter the solution. Allowit to cool. Do not disturb the solutionwhen it is cooling. Look at the solutionafter some time. Can you see the crystalsof copper sulphate? If not, wait for somemore time.Copper sulphateCrystalsFig. 6.6 Crystals of copper sulphate64SCIENCE

www.GOALias.blogspot.comYou have learnt about physical andchemical changes. Try to identifychanges that you observe around youas physical or chemical changes.KeywordsChemical changeChemical reactionCrystallisationGalvanisationPhysical changeRustingWhat you have learnt• Changes can be of two types, physical and chemical.• Physical changes are changes in the physical properties of substances.No new substances are formed in these changes. These changes maybe reversible.• In chemical changes new substances are produced.• Some substances can be obtained in pure state from their solutions bycrystallisation.Exercises1. Classify the changes involved in the following processes as physical orchemical changes:(a) Photosynthesis(b) Dissolving sugar in water(c) Burning of coal(d) Melting of wax(e) Beating aluminium to make aluminium foil(f ) Digestion of food2. State whether the following statements are true or false. In case astatement is false, write the corrected statement in your notebook.(a) Cutting a log of wood into pieces is a chemical change. (True/False)(b) Formation of manure from leaves is a physical change. (True/False)PHYSICALAND CHEMICALCHANGES6565

www.GOALias.blogspot.com(c)(d)(e)Iron pipes coated with zinc do not get rusted easily. (True/False)Iron and rust are the same substances. (True/False)Condensation of steam is not a chemical change. (True/False)3. Fill in the blanks in the following statements:(a)(b)(c)(d)(e)When carbon dioxide is passed through lime water, it turns milkydue to the formation of _________.The chemical name of baking soda is _________.Two methods by which rusting of iron can be prevented are_________ and _________.Changes in which only _________ properties of a substance changeare called physical changes.Changes in which new substances are formed are called _________changes.4. When baking soda is mixed with lemon juice, bubbles are formed withthe evolution of a gas. What type of change is it? Explain.5. When a candle burns, both physical and chemical changes take place.Identify these changes. Give another example of a familiar process inwhich both the chemical and physical changes take place.6. How would you show that setting of curd is a chemical chang?7. Explain why burning of wood and cutting it into small pieces areconsidered as two different types of changes.8. Describe how crystals of copper sulphate are prepared.9. Explain how painting of an iron gate prevents it from rusting.10. Explain why rusting of iron objects is faster in coastal areas than indeserts.11. The gas we use in the kitchen is called liquified petroleum gas (LPG). Inthe cylinder it exist as a liquid. When it comes out from the cylinder itbecomes a gas (Change – A) then it burns (Change – B). The followingstatements pertain to these changes. Choose the correct one.(i)(ii)(iii)(iv)Process – A is a chemical change.Process – B is a chemical change.Both processes A and B are chemical changes.None of these processes is a chemical change.12. Anaerobic bacteria digest animal waste and produce biogas (Change – A).The biogas is then burnt as fuel (Change – B). The followingstatements pertain to these changes. Choose the correct one.(i)(ii)Process – A is a chemical change.Process – B is a chemical change.66SCIENCE

www.GOALias.blogspot.com(iii)(iv)Both processes A and B are chemical changes.None of these processes is a chemical change.Extended Learning — Activities and Projects1. Describe two changes that are harmful. Explain why you consider themharmful. How can you prevent them?2. Take three glass bottles with wide mouths. Label them A, B and C. Fillabout half of bottle A with ordinary tap water. Fill bottle B with waterwhich has been boiled for several minutes, to the same level as in A. Inbottle C, take the same boiled water and of the same amount as in otherbottles. In each bottle put a few similar iron nails so that they are completelyunder water. Add a teaspoonful of cooking oil to the water inbottle C so that it forms a film on its surface. Put the bottles away for afew days. Take out nails from each bottle and observe them. Explainyour observations.3. Prepare crystals of alum.4. Collect information about the types of fuels used for cooking in yourarea. Discuss with your teachers/parents/others which fuels are lesspolluting and why.Did you know?Near the Qutub Minar in Delhistands an iron pillar (Fig. 6.7)which is more than 7 metreshigh. It weighs more than 6000 kg.It was built more than 1600 yearsago. After such a long period it hasnot rusted. For its quality of rustresistance it has been examinedby scientists from all parts of theworld. It tells something about theadvances India had made inmetal technology as back as1600 years ago.Fig. 6.7 Iron pillarPHYSICALAND CHEMICALCHANGES6767

www.GOALias.blogspot.com7Weather, Climate andAdaptations of Animals toClimateDo you remember the things thatyou were asked to pack whenyou were heading for a hillstation? When the sky is cloudy, yourparents insist that you carry anumbrella. Have you heard elders in yourfamily discuss the weather beforeplanning a family function? You musthave also heard the experts discussingthe weather before the start of a game.Have you ever wondered why? Theweather may have a profound effect onthe game. It has a profound effect onour lives. Many of our daily activities areplanned based on the weather predictedfor that day. There are daily reports ofthe weather on the television andradio and in the newspapers. But do youknow what this weather really is?In this chapter, we will study aboutthe weather and climate. We will alsosee how different forms of life areadapted to the climate of their habitat.7.1 WEATHERIn Fig. 7.1 a sample of weather reportfrom a newspaper is given.We find that the daily weather reportcarries information about thetemperature, humidity and rainfallduring the past 24 hours. It alsopredicts the weather for the day.Humidity, as you might know, is ameasure of the moisture in air.68Fig. 7.1 A sample of a weather report from anewspaperActivity 7.1I wonder who preparesthese reports!The weather reports are prepared bythe Meteorological Department of theGovernment. This department collectsdata on temperature, wind, etc., andmakes the weather prediction.Cut out the weather reports of the lastweek from any newspaper. If you do notget a newspaper at home borrow fromyour neighbours or friends and copythese reports in your notebook. You canalso collect weather reports from alibrary. Paste all the cut-outs on a whitesheet or on a chart paper.Now record the information from theweather reports collected by you inTable 7.1. The first row is just a sample.Fill all the columns according to the datain the chart that you have prepared.SCIENCE

www.GOALias.blogspot.comTable 7.1Weather data of a weekDateMax.temp. (°C)Min.Min.temp. (°C) humidity (%)Max.humidity(%)Rainfall*(mm)23-08-06 36.2 27.8 54 82*(Rainfall may not be recorded for all the days since it may not rain everyday. Leavethe space for rainfall blank if the data is not available.)Rainfall is measured by aninstrument called the rain gauge. Itis basically a measuring cylinder witha funnel on top to collect rainwater.Do all the seven days have the samemaximum and minimum temperatures,humidity and rainfall? The maximumand minimum temperatures recordedmay be the same for some of the days.However, all the parameters are not thesame on any two days. Over a week theremay be considerable variation. The day-to-day condition of the atmosphereat a place with respect to thetemperature, humidity, rainfall, wind-speed, etc., is called the weather at thatplace. The temperature, humidity, andother factors are called the elements ofthe weather. The weather of a placechanges day after day and week afterweek. That is why we often say, “today’sweather is too humid”, or “the weatherwas warm last week”.The weather is such a complexphenomenon that it can vary over veryshort periods of time. It can happensometimes that it is sunny in themorning, but suddenly clouds appearfrom nowhere and it starts rainingheavily. Or, a heavy rain may vanish ina matter of minutes and give way tobright sunshine. You must have hadseveral such experiences. Try to recallany such experience and share it withyour friends. Since weather is such acomplex phenomenon, it is not easy topredict.Look at the graph given below whichshows the maximum temperaturerecorded during 03 August 2006 to 09August 2006 at Shillong, Meghalaya(Fig. 7.2)., CWEATHEREATHER, , CLIMATEAND ADAPTATIONSOF ANIMALSTO CLIMATE6969

www.GOALias.blogspot.comDateMaximumtemperature03-08-06 26.0°C04-08-06 23.5°C05-08-06 25.0°C06-08-06 22.0°C07-08-06 25.5°C08-08-06 23.3°C09-08-06 24.4°CFig. 7.2 Graph showing the variation of maximum temperature during 03 to 09 August 2006As it is clear from any weather report,the maximum and minimumtemperatures are recorded every day. Doyou know how these temperatures arerecorded. In Chapter 4 you have learntI wonder why weatherchanges so frequently!What is the source of weatherin the first place?that there are special thermometers forthis purpose, called maximum andminimum thermometers. Can youguess when during the day we have themaximum temperature and when theminimum?The maximum temperature of the dayoccurs generally in the afternoon whilethe minimum temperature occursgenerally in the early morning. Can younow understand why in summers we feelso miserable in the afternoon andcomparatively comfortable early in themorning?All changes in the weather are caused by the sun. The sun is a huge sphere ofhot gases at a very high temperature. The distance of the sun from us is verylarge. Even then the energy sent out by the sun is so huge that it is the source ofall heat and light on the earth. So, the sun is the primary source of energy thatcauses changes in the weather. Energy absorbed and reflected by the earth’ssurface, oceans and the atmosphere play important roles in determining theweather at any place. If you live near the sea, you would have realised that theweather at your place is different from that of a place in a desert, or near a mountain.70SCIENCE

www.GOALias.blogspot.comWhat about the times of sunrise andsunset? You know that in winters itbecomes dark early and you do not getmuch time to play. Are the days shorterin winter than in summer? Try to findit out yourself by completing the projectgiven at the end of the chapter.7.2 C7.2 CLIMATEMeteorologists record the weather everyday. The records of the weather havebeen preserved for the past severaldecades. These help us to determine theweather pattern at a place. The averageweather pattern taken over a longtime, say 25 years, is called theclimate of the place. If we find thatthe temperature at a place is high mostTable 7.2 Srinagar (Jammu &Kashmir)Information about climateMonthMean temperatureMeanoCtotalDailyDailyrainfallminimummaximum(mm)Jan -2.3 4.7 57Feb -0.6 7.8 65Mar 3.8 13.6 99Apr 7.7 19.4 88May 10.7 23.8 72Jun 14.7 29.2 37July 8.2 30.0 49Aug 17.5 29.7 70Sep 12.9 27.8 33Oct 6.1 21.9 36Nov 0.9 14.7 27Dec -1.6 8.2 43of the time, then we say that the climateof that place is hot. If there is also heavyrainfall on most of the days in the sameplace, then we can say that the climateof that place is hot and wet.In Table 7.2 and 7.3, we have giventhe climatic condition at two places inIndia. The mean temperature for a givenmonth is found in two steps. First wefind the average of the temperaturesrecorded during the month. Second, wecalculate the average of such averagetemperatures over many years. Thatgives the mean temperature. The twoplaces are: Srinagar in Jammu andKashmir, and Thiruvananthapuram inKerala.Table 7.3 Thiruvananthapuram(Kerala)Information about climateMonthMean temperatureMeanoCtotalDailyDailyrainfallminimummaximum(mm)Jan 22.2 31.5 23Feb 22.8 31.9 24Mar 24.1 32.6 40Apr 24.9 32.6 117May 24.7 31.6 230Jun 23.5 29.7 321July 23.1 29.2 227Aug 23.2 29.4 138Sep 23.3 30.0 175Oct 23.3 29.9 282Nov 23.1 30.3 185Dec 22.6 31.0 66(Note: The numbers for the mean total rainfall have been rounded off), CWEATHEREATHER, , CLIMATEAND ADAPTATIONSOF ANIMALSTO CLIMATE7171

www.GOALias.blogspot.comBy looking at Tables 7.2 and 7.3 wecan easily see the difference in theclimate of Jammu & Kashmir andKerala. We can see that Kerala is veryhot and wet in comparison to Jammu& Kashmir, which has a moderately hotand wet climate for a part of the year.Similar data for the western regionof India, for example Rajasthan, willshow that the temperature is highduring most part of the year. But duringwinter, which lasts only for a fewmonths, the temperature is quite low.This region receives very littlerainfall. This is the typical desertclimate. It is hot and dry. The northeasternIndia receives rain for a majorpart of the year. Therefore, we can saythat the climate of the north-east is wet.7.3 C7.3 CLIMATEAND ADAPTATIONClimate has a profound effect on allliving organisms.Animals are adapted to survive in theconditions in which they live. Animalsliving in very cold and hot climate mustpossess special features to protectthemselves against the extreme cold orheat. Recall from Chapter 9 of yourClass VI science book the definition ofadaptation. Features and habits thathelp animals to adapt to theirsurroundings are a result of the processof evolution.In Chapter 9 you will learn about theeffect of weather and climate on soil.Here we study the effect of climate onanimals only. In Class VI, you have readabout adaptations of animals to certainhabitats. As examples of adaptation ofanimals to climatic conditions, wediscuss only animals living in polarregions and tropical rainforests.As the name suggests, the polarregions are situated near the poles, i.e.,north pole and south pole.Some well-known countries thatbelong to the polar regions are Canada,Greenland, Iceland, Norway, Sweden,Finland, Alaska in U.S.A. and Siberianregion of Russia.Examples of some countries wherethe tropical rainforests are found areIndia, Malaysia, Indonesia, Brazil,Republic of Congo, Kenya, Uganda, andNigeria.Activity 7.2Take an outline map of the world. Markthe polar regions in blue. Similarly,mark the tropical regions in red.(i) The polar regionsThe polar regions present an extremeclimate. These regions are covered withsnow and it is very cold for most part ofthe year. For six months the sun doesnot set at the poles while for the othersix months the sun does not rise. Inwinters, the temperature can be as lowas –37°C. Animals living there haveadapted to these severe conditions. Letus see how they are adapted byconsidering the examples of polar bearsand penguins.Polar bears have white fur so thatthey are not easily visible in the snowywhite background. It protects them from72SCIENCE

www.GOALias.blogspot.comtheir predators. It also helps them incatching their prey. To protect themfrom extreme cold, they have two thicklayers of fur. They also have a layer offat under their skin. In fact, they are sowell-insulated that they have to moveslowly and rest often to avoid gettingoverheated.Physical activities on warm daysnecessitate cooling. So, the polar beargoes for swimming. It is a goodswimmer. Its paws are wide and large,which help it not only to swim well butalso walk with ease in the snow. Whileswimming under water, it can close itsnostrils and can remain under water forlong durations. It has a strong sense ofsmell so that it can catch its preyfor food. We can understand theadaptations of polar bears with the helpof the flow chart shown in Fig. 7.3.Another well-known animal living inthe polar regions is the penguin(Fig. 7.4). It is also white and mergeswell with the white background. It alsohas a thick skin and a lot of fat to protectit from cold. You may have seen picturesof penguins huddled together. This theydo to keep warm. Recall how warm youfeel when you are in a hall full of people.Fig. 7.4 Penguins huddled togetherFig. 7.3 Adaptations of polar bear, CWEATHEREATHER, , CLIMATEAND ADAPTATIONSOF ANIMALSTO CLIMATE7373

www.GOALias.blogspot.comFig. 7.5 Feet of penguinLike polar bears, penguins are also goodswimmers. Their bodies are streamlinedand their feet have webs, making themgood swimmers (Fig. 7.5).Other animals living in the polarregions are many types of fishes, muskoxen, reindeers, foxes, seals, whales,and birds. It is to be noted that whilefish can remain under cold water forlong, birds must remain warm tosurvive. They migrate to warmer regionswhen winter sets in. They come backafter the winter is over. You knowprobably that India is one of thedestinations of many of these birds. Youmust have seen or heard about theSiberian crane that comes from Siberiato places like Bharatpur in Rajasthanand Sultanpur in Haryana, and someDo fishes and butterfliesalso migrate like birds?Fig. 7.6 Migratory birdsin their habitat/ Migratorybirds in flightDid you know?Some migratory birds travel as much as 15000 km to escape the extreme climaticconditions at home. Generally they fly high where the wind flow is helpful andthe cold conditions allow them to disperse the heat generated by their flightmuscles. But how these birds travel to the same place year after year is still amystery. It seems that these birds have a built–in sense of direction and know inwhich direction to travel. Some birds probably use landmarks to guide them. Manybirds may be guided by the sun during the day and stars at night. There is someevidence that birds may use the magnetic field of the earth to find direction. Andit is not only birds that migrate; mammals, many types of fish and insects arealso known to migrate seasonally in search of more hospitable climates.74SCIENCE

www.GOALias.blogspot.comwetlands of north east and some otherparts of India (Fig. 7.6).(ii) The tropical rainforestsThe tropical region has generally a hotclimate because of its location aroundthe equator. Even in the coldest monththe temperature is generally higher thanabout 15°C. During hot summers, thetemperature may cross 40°C. Days andnights are almost equal in lengththroughout the year. These regions getplenty of rainfall. An important featureof this region is the tropical rainforests.Tropical rainforests are found inWestern Ghats and Assam in India,Southeast Asia, Central America andCentral Africa. Because of continuouswarmth and rain, this region supportswide variety of plants and animals. Themajor types of animals living in therainforests are monkeys, apes, gorillas,lions, tigers, elephants, leopards, lizards,snakes, birds and insects.Let us read about the adaptations ofthese animals to a hot, humid climate.The climatic conditions in rainforestsare highly suitable for supporting anenormous number and variety ofanimals.Since the numbers are large, thereis intense competition for food andshelter. Many animals are adapted toliving on the trees. Red-eyed frog(Fig. 7.7) has developed sticky pads onits feet to help it climb trees on which itlives. To help them live on the trees,monkeys (Fig. 7.8) have long tails forgrasping branches. Their hands and feetFig. 7.7 Red-eyed frogFig. 7.8 A new world monkeyare such that they can easily hold on tothe branches.As there is competition for food, someanimals are adapted to get food noteasily reachable. A striking example isthat of the bird Toucan (Fig. 7.9), whichpossesses a long, large beak. This helpsa toucan to reach the fruits on brancheswhich are otherwise too weak to supportits weight.Many tropical animals have sensitivehearing, sharp eyesight, thick skin anda skin colour which helps them tocamouflage by blending with thesurroundings. This is to protect themfrom predators. For example, big cats, CWEATHEREATHER, , CLIMATEAND ADAPTATIONSOF ANIMALSTO CLIMATE7575

www.GOALias.blogspot.comFig. 7.9 Toucan Fig. 7.10 Lion-tailedmacaque(lions and tigers) have thick skins andsensitive hearing.The lion-tailed macaque (also calledBeard ape) lives in the rainforests ofWestern Ghats (Fig. 7.10). Its mostoutstanding feature is the silver-whitemane, which surrounds the head fromthe cheeks down to its chin. It is a goodclimber and spends a major part of itslife on the tree. It feeds mainly on fruits.It also eats seeds, young leaves, stems,flowers and buds. This beard ape alsosearches for insects under the bark ofthe trees. Since it is able to get sufficientfood on the trees, it rarely comes downon the ground.Another well-known animal of Indiantropical rainforest is the elephant(Fig. 7.11). It has adapted to theconditions of rainforests in manyremarkable ways. Look at its trunk. Ituses it as a nose because of which ithas a strong sense of smell. The trunkis also used by it for picking up food.Moreover, its tusks are modified teeth.These can tear the bark of trees thatelephant loves to eat. So, the elephantis able to handle the competition for foodrather well. Large ears of the elephanthelp it to hear even very soft sounds.They also help the elephant to keep coolin the hot and humid climate of therainforest.Fig. 7.11 An Indian elephantKeywordsAdaptationClimateElements of weatherHumidityMaximum temperatureMigrationMinimum temperaturePolar regionTropical rainforestTropical regionWeather76SCIENCE

www.GOALias.blogspot.comWhat you have learnt• The day-to-day condition of the atmosphere at a place with respect tothe temperature, humidity, rainfall, wind-speed, etc., is called theweather at that place.• The weather is generally not the same on any two days and week afterweek.• The maximum temperature of the day occurs generally in the afternoonwhile the minimum temperature occurs in the early morning.• The times of sunrise and sunset also change during the year.• All the changes in the weather are driven by the sun.• The average weather pattern taken over a long time, say 25 years, iscalled the climate of the place.• The tropical and the polar regions are the two regions of the earth,which have severe climatic conditions.• Animals are adapted to the conditions in which they live.• The polar regions are very cold throughout the year. The sun does notset for six months in a year and in the other six months it does not rise.• Animals in the polar region are adapted to the extremely cold climate byhaving some special characteristics such as white fur, strong sense ofsmell, a layer of fat under the skin, wide and large paws for swimmingand walking, etc.• Migration is another means to escape the harsh, cold conditions.• Because of the hospitable climatic conditions huge populations of plantsand animals are found in the tropical rainforests.• Animals in the tropical rainforests are adapted such that they eatdifferent kinds of food to overcome the competition for food and shelter.• Some adaptations of animals living in the tropical rainforests includeliving on the trees, development of strong tails, long and large beaks,bright colours, sharp patterns, loud voice, diet of fruits, sensitive hearing,sharp eyesight, thick skin, ability to camouflage in order to protectthemselves from predators, etc.Exercises1. Name the elements that determine the weather of a place.2. When are the maximum and minimum temperature likely to occurduring the day?3. Fill in the blanks:(i) The average weather taken over a long time is called ___________., CWEATHEREATHER, , CLIMATEAND ADAPTATIONSOF ANIMALSTO CLIMATE7777

www.GOALias.blogspot.com(ii)(iii)A place receives very little rainfall and the temperature ishigh throughout the year, the climate of that place will be___________ and ___________ .The two regions of the earth with extreme climatic conditions are___________ and __________.4. Indicate the type of climate of the following areas:(a)Jammu and Kashmir: _________________________________(b) Kerala: ____________________________________________(c) Rajasthan: __________________________________________(d) North-east India: _____________________________________5. Which of the two changes frequently, weather or climate?6. Following are some of the characteristics of animals:(i) Diets heavy on fruits (ii) White fur(iii) Need to migrate (iv) Loud voice(v) Sticky pads on feet (vi) Layer of fat under skin(vii) Wide and large paws (viii) Bright colours(ix) Strong tails (x) Long and large beakFor each characteristic indicate whether it is adaptation for tropicalrainforests or polar regions. Do you think that some of thesecharacteristics can be adapted for both regions?7. The tropical rainforest has a large population of animals. Explain whyit is so.8. Explain, with examples, why we find animals of certain kind living inparticular climatic conditions.9. How do elephant living in the tropical rainforest adapt itself.Choose the correct option which answers the following question:10. A carnivore with stripes on its body moves very fast while catching itsprey. It is likely to be found in(i) polar regions (ii) deserts(iii) oceans (iv) tropical rainforests11. Which features adapt polar bears to live in extremely cold climate?(i)(ii)(iii)(iv)A white fur, fat below skin, keen sense of smell.Thin skin, large eyes, a white fur.A long tail, strong claws, white large paws.White body, paws for swimming, gills for respiration.78SCIENCE

www.GOALias.blogspot.com12. Which option best describes a tropical region?(i) hot and humid(ii) moderate temperature, heavy rainfall(iii) cold and humid(iv) hot and dryExtended Learning — Projects and Activities1. Collect weather reports of seven successive days in the winter months(preferably December). Collect similar reports for the summer months(preferably June). Now prepare a table for sunrise and sunset times asshown:TableJuneDecemberDate Sunrise Sunset Date Sunrise SunsetTry to answer the following questions:(i)(ii)(iii)(iv)(v)(vi)(vii)Is there any difference in the time of sunrise during summer andwinter?When do you find that the sun rises earlier?Do you also find any difference in the time of sunset during themonth of June and December?When are the days longer?When are the nights longer?Why are the days sometimes longer and sometimes shorter?Plot the length of the day against the days chosen in June andDecember.(Instructions for plotting graphs are given in Chapter 13.)2. Collect information about the Indian Meteorological Department. Ifpossible visit its website: http//www.imd.gov.in.Write a breif report about the things this department does.Did you know?Rainforests cover about 6% of the earth’s surface, but they have morethan half of the animal life and about two-thirds of the flowering plantsof the planet. However, much of this life is still unknown to us., CWEATHEREATHER, , CLIMATEAND ADAPTATIONSOF ANIMALSTO CLIMATE7979

www.GOALias.blogspot.com8Winds, Storms and CyclonesOrissa was hit by a cyclone withwind speed of 200 km/h on18 October 1999. The cyclonesmashed 45,000 houses making7,00,000 people homeless. On29 October the same year, a secondcyclone with wind speed of 260 km/hhit Orissa again. It was accompanied bywater waves about 9 m high. Thousandsof people lost their lives. Property worthcrores of rupees was destroyed. Thecyclone affected agriculture, transport,communication, and electricity supply.Fig. 8.1 Image taken by a satellite of a cycloneapproaching the coast of OrissaCourtesy: India Meteorological Department,New Delhi80But, what are cyclones? How arethey formed? Why are they sodestructive? In this chapter we shallseek answers to some of these questions.We begin with some activitiesinvolving air. These activities will clarifysome basic features concerning acyclone. Before we begin, remember thatthe moving air is called the wind.8.1 A8.1 AIREXERTSPRESSUREActivity 8.1Whenever an activity involves heating,be very careful. It is advised that suchactivities are performed in thepresence of an elderly person fromyour family. Or, carry out theseactivities in the presence of yourteacher.You need to boil water in the followingactivity.Take a tin can with a lid. Fill itapproximately half with water. Heat thecan on a candle flame till the water boils.Let the water boil for a few minutes. Blowout the candle. Immediately put the lidtightly on the can. Be careful in handlingthe hot can. Put the can carefully in ashallow metallic vessel or a washbasin.Pour fresh water over the can.What happens to the shape of the can?SCIENCE

www.GOALias.blogspot.comFig. 8.2 Can with hot water being cooledCan you guess why the shape of thecan gets distorted?If you cannot get a tin can, take asoft plastic bottle. Fill it with hot water.Empty the bottle and immediately capit tightly. Place the bottle under runningwater.Recall now some of your experiences.When you fly a kite, does the windcoming from your back help?If you are in a boat, is it easier torow it if there is wind coming frombehind you?Do you find it difficult to ride a bicycleagainst the direction of the wind.You know that we have to fill air intothe bicycle tube to keep it tight. Also,you know that a bicycle tube overfilledwith air may burst. What is the air doinginside the tube?Discuss with your friends how theair in the bicycle tube keeps it in shape.All these experiences show that theair exerts pressure. It is due to thispressure that the leaves of trees,banners, or flags flutter when the windis blowing. You can list some moreexperiences which show that the air haspressure.Let us now try to explain why thecan (or the bottle) gets distorted. Aswater is poured over the can, somesteam in the can condenses into water,reducing the amount of air inside. Thepressure of air inside the can decreasesthan the pressure exerted by the airfrom outside the can. As a result thecan gets compressed.This activity again confirms that airexerts pressure.8.2 HIGHSPEEDWINDSAREACCOMPANIEDBY REDUCEDAIRPRESSUREActivity 8.2Fig. 8.3 Blowing into the bottleCrumple a small piece of paper intoa ball of size smaller than the mouth ofan empty bottle. Hold the empty bottleon its side and place the paper ball justinside its mouth. Now try to blow onthe ball to force it into the bottle. Trythe activity with bottles of different sizes.Challenge your friends if they can force, SWINDSINDS, , STORMSAND CYCLONES8181

www.GOALias.blogspot.comthe paper ball in by blowing into thebottle.Paheli and Boojho are thinking aboutthe following question:Why is it difficult to force the paperball into the bottle?Activity 8.3Blow the balloonsTake two balloons of approximatelyequal size. Put a little water into thePaheli thinks that the strip will belifted up. Boojho thinks that the stripwill bend down.82Fig. 8.4 Blowing between the balloonsballoons. Blow up both the balloons andtie each one to a string. Hang theballoons 8–10 cm apart on a cycle spokeor a stick. Blow in the space betweenthe balloons.What did you expect? Whathappens?Try different ways of blowing on theballoons to see what happens.Activity 8.4Can you blow and lift?Hold a strip of paper, 20 cm long and3 cm wide, between your thumb andforefinger as shown in the Fig. 8.5. Nowblow over the paper.Fig. 8.5 Blowing over a strip of paperWhat do you think will happen tothe paper?Let us try to understand theobservations in Activities 8.2, 8.3 and 8.4.Were the observations along the linesyou thought? Do you get the feelingthat the increased wind speed isaccompanied by a reduced air pressure?When we blow into the mouth of thebottle, the air near the mouth has higherspeed. This decreases the pressurethere. The air pressure inside the bottleis higher than near the mouth. The airinside the bottle pushes the ball out.In Activity 8.3 you saw that when youblew between the balloons, they movedSCIENCE

www.GOALias.blogspot.comtowards each other. How could thishappen? This could happen if thepressure of air between the balloonswere somehow reduced. The pressureoutside the balloons would then pushthem towards each other.In Activity 8.4 you saw that when youblew over the paper strip, it wentupwards. Again, this could happen ifblowing over the paper reduced the airpressure above the strip.We see that the increased windspeed is, indeed, accompanied by areduced air pressure.Can you imagine what would happenif high-speed winds blew over the roofsof buildings? If the roofs were weak, theycould be lifted and blown away. If youhave any such experience, share it withyour friends.Let us try to understand how windsare produced, how they bring rain andhow they can be destructive sometimes.You already know that when airmoves, it is called wind. Air moves fromBalloon tied overthe neck of theboiling tubeBoiling tubeimmersed inhot waterFig. 8.6 The shape of the balloon in hot and cold waterthe region where the air pressure ishigh to the region where the pressureis low. The greater the difference inpressure, the faster the air moves. Buthow are the pressure differences createdin nature? Is the difference intemperature involved? The followingactivities will help you to understandthis.8.3 AIREXPANDSON HEATINGBoiling tubeimmersed inice-cold waterActivity 8.5Take a boiling tube. Stretch a balloontightly over the neck of the tube. Youcan use a tape to make it tight. Poursome hot water in a beaker. Insert theboiling tube with the balloon in the hotwater. Observe for 2–3 minutes for anychange in shape of the balloon. Take thetube out, let it cool down to the roomtemperature. Take some ice-cold waterin another beaker and place the tubewith the balloon in cold water for 2–3minutes. Observe the change in theshape of the balloon.Think and try to answer:What makes the ballooninflated when the boiling tubeis placed in hot water?Why is the same balloondeflated when the tube is keptin cold water?Can we infer from the firstobservation that air expandson heating? Can you now statewhat happens to the air in theboiling tube when it coolsdown?, SWINDSINDS, , STORMSAND CYCLONES8383

www.GOALias.blogspot.comThe next activity is very interesting.This will make you understand moreabout hot air.Activity 8.6Take two paper bags or empty paper cupsof the same size. Hang the two bags inCAUTIONHandle the burning candle carefully.Fig. 8.7 Hot air rising upthe inverted position on the two ends ofa metal or wooden stick.Tie a piece of thread in the middle ofthe stick. Hold the stick by the thread(Fig. 8.7) as in a balance. Put a burningcandle below one of the bags as shownin the figure. Observe what happens.Why is the balance of the bagsdisturbed?Does this activity indicate that warmair rises up? As the warm air rises up,it pushes the bag above the candle. Doesthe disturbance of the balance suggestthat the warm air is lighter than the coldair?Can you now explain why smokealways rises up?Also, it is important to remember thaton heating the air expands and occupiesmore space. When the same thingoccupies more space, it becomes lighter.The warm air is, therefore, lighter thanthe cold air. That is the reason that thesmoke goes up.In nature there are several situations,where warm air rises at a place. The airpressure at that place is lowered. Thecold air from the surrounding areasrushes in to fill its place. This sets upconvection in air, as you learnt inChapter 4.8.4 WINDCURRENTSARE GENERATEDDUETO UNEVENHEATINGONTHE EARTHThese situations are:(a)Uneven heating betweenthe equator and the polesYou might have learnt in Geography thatregions close to the equator getmaximum heat from the Sun. The airin these regions gets warm. The warmair rises, and the cooler air from the84SCIENCE

www.GOALias.blogspot.comregions in the 0–30 degrees latitude belton either side of the equator moves in.These winds blow from the north andthe south towards the equator. At thepoles, the air is colder than that atlatitudes about 60 degrees. The warmair at these latitudes rises up and thecold wind from the polar regions rushesin, to take its place. In this way, windcirculation is set up from the poles tothe warmer latitudes, as shown inFig. 8.8.(b)Uneven heating of landand waterYou have read about the sea breeze andthe land breeze in Chapter 4.In summer, near the equator the landwarms up faster and most of the timethe temperature of the land is higherthan that of water in the oceans. Theair over the land gets heated and rises.This causes the winds to flow from theoceans towards the land. These aremonsoon winds (Fig. 8.9).The word monsoon is derived from theArabic word ‘mausam’, which means‘season’.In winter, the direction of the windflow gets reversed; it flows from the landto the ocean (Fig. 8.10).I want to know what thesewinds do for us.Fig. 8.8 The wind flow pattern because ofuneven heating on the earthI wonder why the winds shownin the figure are not in the exactnorth-south direction.The winds would have flown in thenorth-south direction from north tosouth, or from south to north. A changein direction is however, caused by therotation of the earth.The winds from the oceans carrywater and bring rain. It is a part of thewater cycle.The monsoon winds carry waterand it rains.Clouds bring rain and give ushappiness. Farmers in our countrydepend mainly on rains for theirharvests. There are many folk songsassociated with clouds and rain. Singand enjoy with your friends, if you knowsuch a song. Here is one for you., SWINDSINDS, , STORMSAND CYCLONES8585

www.GOALias.blogspot.comRoaring clouds across the skyTell us that monsoon’s hereDark and floating clouds then pourRaindrops every where.Clouds make lightning flash overheadAnd irrigate fields with rainClouds make earth, its fragrance spreadWhen wet with drops of rain.Rising from the ocean vastClouds fill up with rainRain to ocean, back at lastTo mingle with ocean again!However, it is not always a happyending. Rains often create problems.Can you list some of the problems?You can discuss the causes andsolutions of the problems with yourteacher and parents.In nature itself there are certainsituations that can sometimes createdisasters and pose threat to humans,animals and plant life.Let’s study two such situations —thunderstorms and cyclones.Fig. 8.9 Uneven heating of land especially theRajasthan desert generates monsoon winds fromsouthwest direction in summer. These windscarry lots of water from the Indian Ocean.Fig. 8.10 Uneven heating of land and water inwinter generate winds from the northwestcolder land. These colder winds carry littlewater, hence bring small amount of rain inwinter.Courtesy: India Meteorological Department, New Delhi86SCIENCE

www.GOALias.blogspot.com8.5 T8.5 THUNDERSTORMSAND CYCLONESThunderstorms develop in hot, humidtropical areas like India very frequently.The rising temperatures produce strongupward rising winds. These winds carrywater droplets upwards, where theyfreeze, and fall down again. The swiftmovement of the falling water dropletsalong with the rising air create lightningand sound. It is this event that we call athunderstorm. You will read aboutlightning in higher classes.If a storm is accompanied bylightning, we must take the followingprecautions:• Do not take shelter under anisolated tree. If you are in a foresttake shelter under a small tree. Donot lie on the ground.• Do not take shelter under anumbrella with a metallic end.• Do not sit near a window. Opengarages, storage sheds, metalsheds are not safe places to takeshelter.• A car or a bus is a safe place totake shelter.• If you are in water, get out and goinside a building.How a thunderstorm becomesa cycloneYou know that water requires heat whenit changes from liquid to vapour state.Does the water give back heat whenvapour condenses into liquid? Can yourecall any experience to support this?Structure of a cycloneThe centre of a cyclone is a calm area.It is called the eye of the storm. A largecyclone is a violently rotating mass ofair in the atmosphere, 10 to 15 kmhigh. The diameter of the eye variesfrom 10 to 30 km (Fig. 8.11). It is aregion free of clouds and has lightwinds. Around this calm and clear eye(Fig. 8.12), there is a cloud region ofabout 150 km in size. In this regionthere are high-speed winds (150–250km/h) and thick clouds with heavyrain. Away from this region the windspeed gradually decreases. Theformation of a cyclone is a verycomplex process. A model is shown inFig. 8.11.Before cloud formation, water takesup heat from the atmosphere to changeinto vapour. When water vapour changesback to liquid form as raindrops, thisheat is released to the atmosphere. Theheat released to the atmosphere warmsthe air around. The air tends to rise andcauses a drop in pressure. More airrushes to the centre of the storm. Thiscycle is repeated. The chain of eventsends with the formation of a verylow-pressure system with veryhigh-speed winds revolving around it.It is this weather condition that we calla cyclone. Factors like wind speed,wind direction, temperature andhumidity contribute to the developmentof cyclones., SWINDSINDS, , STORMSAND CYCLONES8787

www.GOALias.blogspot.comFig. 8.12 The image of the‘eye’ of a cycloneFig. 8.11 Formation of a cycloneFig. 8.13 Rising water caused bya cyclone.Courtesy: India Meteorological Department, New Delhi8.6 D8.6 DESTRUCTIONCAUSEDBYCYCLONESCyclones can be very destructive.Strong winds push water towards theshore even if the storm is hundreds ofkilometres away. These are the firstindications of an approaching cyclone.The water waves produced by the windare so powerful that a person cannotovercome them.The low pressure in the eye liftswater surface in the centre. The risingwater may be as high as 3–12 metres(Fig. 8.13). It appears like a water-wallmoving towards the shore. As a result,the seawater enters the low-lying coastalareas, causing severe loss of life andproperty. It also reduces the fertility ofthe soil.Continuous heavy rainfall mayfurther worsen the flood situation.High-speed winds accompanying acyclone can damage houses, telephonesand other communication systems,trees, etc., causing tremendous loss oflife and property.88SCIENCE

www.GOALias.blogspot.comA cyclone is known bydifferent names in differentparts of the world. It iscalled a ‘hurricane’ in theAmerican continent. InPhilippines and Japan itis called a ‘typhoon’(Fig. 8.14).NorthPacific OceanTyphoonCycloneHurricaneNorthAtlantic OceanHurricaneCycloneFig. 8.14 Regions near theequator where cyclones form.Cyclones are worldwidephenomena.SouthPacific OceanNorthAtlantic OceanIndian OceanThe diameter of atornado can be assmall as a metre and aslarge as a km, or evenwider. The funnel of atornado sucks dust,Fig. 8.15 Protectingdebris and everythingfrom a tornadonear it at the base (dueto low pressure) and throws them out near the top.Here are a few accounts of the survivors of tornados-(from Discovery channel’s “Young DiscoverySeries”).“I saw the cloud coming and tried to take shelterinside. But as soon as I reached for the doorknob,the house took off into the sky. I was not hurt atall.”“After the storm we had to clean the debris fromthe wheat fields. We picked up splintered boardsand tree branches as well as dead chickens withtheir feathers blown off and rabbits looked like theyhad been skinned.”A tornado shelter is a room situated deep insideor underground having no windows. Or otherwiseit is better to shut windows and take shelter undera table, workbench, where debris cannot reach. Onehas to bow down on knees protecting head andneck using arms (Fig. 8.15).Tornadoes: In our countrythey are not very frequent. Atornado is a dark funnelshaped cloud that reachesfrom the sky to the ground(Fig. 8.16). Most of thetornadoes are weak. A violenttornado can travel at speedsof about 300 km/h.Tornadoes may form withincyclones.The whole coastline ofIndia is vulnerable tocyclones, particularly theeast coast. The west coast ofIndia is less vulnerable tocyclonic storms both interms of intensity andfrequency of the cyclones.8.7 EFFECTIVESAFETYMEASURES• A cyclone forecast andwarning service.• Rapid communicationof warnings to the, SWINDSINDS, , STORMSAND CYCLONES8989

www.GOALias.blogspot.comFig. 8.16 Image of a tornado[National Severe Storm Laboratory (NSSL)]Courtesy: India Meteorological Department,New DelhiWe have learnt that all storms are lowpressuresystems. Wind speed playsan important role in the formation ofstorms. It is, therefore, important tomeasure the wind speed. Theinstrument that measures the windspeed is called an anemometer.Fig. 8.17 An anemometer for measuring thespeed of windCourtesy: India Meteorological Department,New DelhiGovernment agencies, the ports,fishermen, ships and to the generalpublic.• Construction of cyclone shelters inthe cyclone prone areas, andAdministrative arrangements formoving people fast to safer places.Action on the part of thepeople• We should not ignore the warningsissued by the meteorologicaldepartment through TV, radio, ornewspapers.• We should —make necessary arrangements toshift the essential household goods,domestic animals and vehicles, etc.to safer places;avoid driving on roads throughstanding water, as floods may havedamaged the roads; andkeep ready the phone numbers of allemergency services like police, firebrigade, and medical centres.Some other precautions, if you arestaying in a cyclone hit area —• Do not drink water that could becontaminated. Always store drinkingwater for emergencies.• Do not touch wet switches and fallenpower lines.• Do not go out just for the sake of fun.• Do not pressurise the rescue forceby making undue demands.• Cooperate and help your neighboursand friends.8.8 ADVANCEDTECHNOLOGYHASHELPEDThese days we are better protected. Inthe early part of the last century, coastal90SCIENCE

www.GOALias.blogspot.comresidents may have had less than aday to prepare or evacuate theirhomes from an oncoming cyclone.The world today is very different.Thanks to satellites and radars, aCyclone alert or Cyclone watch isissued 48 hours in advance of anyexpected storm and a Cyclone warningis issued 24 hrs in advance. Themessage is broadcast every hour or halfhour when a cyclone is nearer the coast.Several national and internationalorganisations cooperate to monitor thecyclone-related disasters.KeywordsAnemometerCycloneHurricaneLightningLow pressureMonsoon windsPressureThunderstormsTornadoTyphoonWind flow patternWhat you have learnt• Air around us exerts pressure.• Air expands on heating and contracts on cooling.• Warm air rises up, whereas comparatively cooler air tends to sink towardsthe earth’s surface.• As warm air rises, air pressure at that place is reduced and the coolerair moves to that place.• The moving air is called wind.• Uneven heating on the earth is the main cause of wind movements.• Winds carrying water vapour bring rain.• High-speed winds and air pressure difference can cause cyclones.• It has become easier to monitor cyclones with the help of advancetechnology like satellites and radars.• Self-help is the best help. Therefore it is better to plan in advance andbe ready with defence against any approaching cyclone.• The following flow chart will help you to understand the phenomenathat lead to the formation of clouds and falling of rain and creation ofstorms and cyclones:, SWINDSINDS, , STORMSAND CYCLONES9191

www.GOALias.blogspot.comDifference of temperature between two regionsSets convection in airWarm air rises, creating a low-pressure areaCool air converges to the low-pressure areaWarm air rises, cools and the water vapourcondenses to form cloudsThe bigger water drops in the cloud fall to theground as rain, hail or snowFalling water droplets and rising air move vigorouslyto produce thunderstormUnder certain weather condition storms maydevelop into cyclonesExercises1. Fill the missing word in the blank spaces in the following statements:(a)(b)(c)Wind is —————— air.Winds are generated due to —————— heating on the earth.Near the earth’s surface __________air rises up whereas___________ air comes down.(d) Air moves from a region of ——— pressure to a region of ———pressure.2. Suggest two methods to find out wind direction at a given place.3. State two experiences that made you think that air exerts pressure(other than those given in the text).4. You want to buy a house. Would you like to buy a house having windowsbut no ventilators? Explain your answer.5. Explain why holes are made in hanging banners and hoardings.6. How will you help your neighbours in case cyclone approaches yourvillage/town?7. What planning is required in advance to deal with the situation createdby a cyclone?8. Which one of the following place is unlikely to be affected by a cyclone.(i) Chennai (ii) Mangaluru (Mangalore)92SCIENCE

www.GOALias.blogspot.com(iii) Amritsar (iv) Puri9. Which of the statements given below is correct?(i)(ii)(iii)(iv)In winter the winds flow from the land to the ocean.In summer the winds flow from the land towards the ocean.A cyclone is formed by a very high-pressure system with veryhigh-speed winds revolving around it.The coastline of India is not vulnerable to cyclones.Extended Learning — Activities and Projects1. You can perform the Activity 8.5 in the chapter slightdifferently at home. Use two plastic bottles of the same size. Stretch oneballoon on the neck of each bottle. Keep one bottle in the sun and theother in the shade. Record your observations. Compare theseobservations and the result with those of Activity 8.5.2. You can make your own anemometer.Collect the following items:4 small paper cups (used ice cream cups), 2 strips of cardboard (20cmlong and 2cm wide), gum, stapler, a sketch pen and a sharpened pencilwith eraser at one end.Take a scale; draw crosses on the cardboard strips as shown in theFig. 8.18. This will give you the centres of the strips.Fig. 8.18 Finding centre of the stripsFig. 8.19 A model of an anemometer, SWINDSINDS, , STORMSAND CYCLONES9393

www.GOALias.blogspot.comFix the strips at the centre, putting one over the other so that theymake a plus (+) sign. Now fix the cups at the ends of the strips. Colourthe outer surface of one cup with a marker or a sketch pen. All the 4cups should face in the same direction.Push a pin through the centre of the strips and attach the strips andthe cups to the eraser of the pencil. Check that the strips rotate freelywhen you blow on the cups. Your anemometer is ready. Counting thenumber of rotations per minute will give you an estimate of the speed ofthe wind. To observe the changes in the wind speed, use it at differentplaces and different times of the day.If you do not have a pencil with attached eraser you can use the tip of aball pen. The only condition is that the strips should rotate freely.Remember that this anemometer will indicate only speed changes. Itwill not give you the actual wind speed.3. Collect articles and photographs from newspapers and magazines aboutstorms and cyclones. Make a story on the basis of what you learnt inthis chapter and the matter collected by you.4. Suppose you are a member of a committee, which is responsible forcreating development plan of a coastal state. Prepare a short speechindicating the measures to be taken to reduce the suffering of the peoplecaused by cyclones.5. Interview eyewitness to collect theactual experience of people affected bya cyclone.6. Take an aluminium tube about 15 cmlong and 1 to 1.5 cm in diameter. Cutslice of a medium-sized potato about2 cm thick. Insert the tube in the slice,press it, and rotate it 2–3 times.Remove the tube. You will find a pieceof potato fixed in the tube like apiston head. Repeat the same processwith the other end of the tube. Nowyou have the tube with both endsclosed by potato pieces with an aircolumn in between. Take a pencil withone end unsharpened. Place this endat one of the pieces of potato. Press itsuddenly to push the potato piece inthe tube. Observe what happens. Theactivity shows rather dramaticallyhow increased air pressure can push things.Fig. 8.20CAUTION: When you perform this activity, make sure that nobody isstanding in front of the tube.94SCIENCE

www.GOALias.blogspot.comYou can read more on the related topics on the following websites:http://www.imd.gov.in/http://library.thinkquest.org/10136/www.bom.gov.au/lam/students_teachers/cycmod.shtmlwww.chunder.com/ski/lightanim.htmlDid you know?A bolt of lightning travels at a speed of more than 400,000 km/h. It canheat the air around it to a temperature which is more than 4 times thetemperature of the surface of the sun. That is what makes lightning sodangerous., SWINDSINDS, , STORMSAND CYCLONES9595

www.GOALias.blogspot.com9SoilSoil is one of the most importantnatural resources. It supports thegrowth of plants by holding theroots firmly and supplying water andnutrients. It is the home for manyorganisms. Soil is essential foragriculture. Agriculture provides food,clothing and shelter for all. Soil is thusan inseparable part of our life. Theearthy fragrance of soil after the first rainis always refreshing.Fig. 9.1 Children playing with soil9.1 S9.1 SOILTEEMINGWITH LIFEOne day during the rainy season Paheliand Boojho observed an earthwormcoming out of the soil. Paheli wonderedwhether there were other organisms alsoin the soil. Let us find out.Activity 9.1Collect some soil samples and observethem carefully. You can use a hand lens.Examine each sample carefully and fillin Table 9.1.• Discuss your observationswith your friends.• Are the soil samplescollected by your friendssimilar to the ones collected byyou?Boojho and Paheli haveused soil in many ways. Theyenjoy playing with it. It is agreat fun indeed.Make a list of the uses of soil.Table 9.1S. Soil sourcePlantsAnimalsNo.1. Garden soil Grass, ………. Ant, ……….2. Soil from the roadside ………………3. Soil from the area whereconstruction is going on ………………4. ……………… ………………5. ……………… ………………Any otherobservations96SCIENCE

www.GOALias.blogspot.comI wonder why I found somepieces of plastic articles andpolythene bags in the soil samplecollected from the roadside andthe garden.and then add a handful of soil to it. Stirit well with a stick to dissolve the soil.Now let it stand undisturbed for sometime (Fig. 9.2). Afterwards, observe it andanswer the following questions:Polythene bags and plastics pollutethe soil. They also kill the organismsliving in the soil. That is why there isa demand to ban the polythene bagsand plastics. Other substances whichpollute the soil are a number of wasteproducts, chemicals and pesticides.Waste products and chemicals shouldbe treated before they are releasedinto the soil. The use of pesticidesshould be minimised.I want to know whether thesoil from a field can be usedto make toys?9.2 S9.2 SOILPROFILESoil is composed of distinct layers.Perform the following activity to find outhow these layers are arranged.Activity 9.2Take a little soil. Break the clumps withyour hand to powder it. Now take a glasstumbler, three quarters filled with water,Fig. 9.2 Layers of soilhumuswaterclaysandgravel• Do you see layers of particles ofdifferent sizes in the glass tumbler?• Draw a diagram showing these layers.• Are there some dead rotting leavesor animal remains floating on water?The rotting dead matter in the soil iscalled humus.You probably know that the soil isformed by the breaking down of rocksby the action of wind, water and climate.This process is called weathering. Thenature of any soil depends upon therocks from which it has been formed andthe type of vegetation that grows in it.A vertical section through differentlayers of the soil is called the soil profile.Each layer differs in feel (texture),SOIL9797

www.GOALias.blogspot.comcolour, depth and chemical composition.These layers are referred to as horizons(Fig. 9.3).soil fertile and provides nutrients togrowing plants. This layer is generallysoft, porous and can retain more water.It is called the topsoil or the A-horizon.A-horizonB-horizonC-horizonBedrockFig. 9.3 Soil profileWe usually see the top surface ofthe soil, not the layers below it. If welook at the sides of a recently dug ditch,we can see the inner layers of the soil,too. Such a view enables us to observethe soil profile at that place. Soil profilecan also be seen while digging a well orlaying the foundation of a building. Itcan also be seen at the sides of a roadon a hill or at a steep river bank.The uppermost horizon is generallydark in colour as it is rich in humusand minerals. The humus makes the98This provides shelter for many livingorganisms such as worms, rodents,moles and beetles. The roots of smallplants are embedded entirely in thetopsoil.The next layer has a lesser amountof humus but more of minerals. Thislayer is generally harder and morecompact and is called the B-horizon orthe middle layer.The third layer is the C-horizon,which is made up of small lumps ofrocks with cracks and crevices. BelowSCIENCE

www.GOALias.blogspot.comthis layer is the bedrock, which is hardand difficult to dig with a spade.9.3 S9.3 SOILTYPESAs you know, weathering of rocksproduces small particles of variousmaterials. These include sand and clay.The relative amount of sand and claydepends upon the rock from which theparticles were formed, that is the parentrock. The mixture of rock particlesand humus is called the soil. Livingorganisms, such as bacteria, plant rootsand earthworm are also important partsof any soil.The soil is classified on the basis ofthe proportion of particles of varioussizes. If soil contains greater proportionof big particles it is called sandy soil.If the proportion of fine particles isrelatively higher, then it is calledclayey soil. If the amount of large andfine particles is about the same, thenthe soil is called loamy. Thus, the soilcan be classified as sandy, clayey andloamy.The sizes of the particles in a soilhave a very important influence on itsproperties. Sand particles are quitelarge. They cannot fit closely together,so there are large spaces between them.These spaces are filled with air. We saythat the sand is well aerated. Water candrain quickly through the spacesbetween the sand particles. So, sandysoils tend to be light, well aerated andrather dry. Clay particles, being muchsmaller, pack tightly together, leavinglittle space for air. Unlike sandy soil,water can be held in the tiny gapsbetween the particles of clay. So claysoils have little air. But they are heavyas they hold more water than the sandysoils.The best topsoil for growing plantsis loam. Loamy soil is a mixture of sand,clay and another type of soil particleknown as silt. Silt occurs as a depositin river beds. The size of the silt particlesis between those of sand and clay. Theloamy soil also has humus in it. It hasthe right water holding capacity for thegrowth of plants.I want to know:What kind of soil should beused for making matkas andsurahis?Activity 9.3Collect samples of clayey, loamy andsandy soils. Take a fistful of soil fromone of the samples. Remove any pebbles,rocks or grass blades from it. Now addwater drop by drop and knead the soil[Fig. 9.4 (a)]. Add just enough water sothat a ball [Fig. 9.4 (b)] can be made fromit, but at the same time it should not besticky. Try to make a ball [Fig. 9.4 (c)]from this soil. On a flat surface, roll thisball into a cylinder [Fig. 9.4 (d)]. Try tomake a ring from this cylinder [Fig. 9.4 (e)].Repeat this activity with other samplesalso. Does the extent to which a soil canbe shaped indicate its type?SOIL9999

www.GOALias.blogspot.com(a)(b)Boojho wondered why therewas a difference in theabsorption of water in thetwo squares.(c)(d)Can you suggest which type of soilwould be the best for making pots, toysand statues?9.4 PROPERTIESOF SOIL(e)Fig. 9.4 Working with the soilYou have listed some uses of soil. Let usperform some activities to find thecharacteristics of the soil.Percolation rate of water insoilBoojho and Paheli marked two differentsquares of 50 cm 50 cm each, one onthe floor of their house and the otheron the kutcha (unpaved) road. They filledtwo bottles of the same size with water.They emptied the water from the bottles,one each, at the same time in the twosquares. They observed that the wateron the floor flowed down and was notabsorbed. On the kutcha road, on theother hand, the water was absorbed.Now let us perform an activity tounderstand this.Activity 9.4For this activity divide yourself intothree teams. Name the teams A, B andC. You will be finding out how fast thewater passes down the soil. You willneed a hollow cylinder or a pipe. Ensurethat each team uses pipes of the samediameter. Some suggestions forobtaining such a pipe are given below:1. If possible, get a small tin can andcut off its bottom.2. If PVC pipe (approx. diameter 5 cm)is available, cut it into 20 cm longpieces and use them.At the place where you collect the soil,place the pipe about 2 cm deep in theground. Pour 200 mL water in the pipeslowly. For measuring 200 mL water youcan use any empty 200 mL bottle. NoteFig. 9.5 Measuring rate of percolation100SCIENCE

www.GOALias.blogspot.comthe time when you start pouring water.When all the water has percolatedleaving the pipe empty, note the timeagain. Be careful not to let the waterspill over or run down on the outside ofthe pipe while pouring. Calculate therate of percolation by using thefollowing formula:amount of water (mL)percolation rate (mL/min) = percolation time (min)StandDropsBoiling tubeSoil sampleFor example, suppose that for acertain sample, it took 20 minutes for200 mL to percolate. So,200 mLrate of percolation = = 10 mL/min20 minCalculate the rate of percolation inyour soil sample. Compare your findingswith others and arrange the soil samplesin the increasing order of the rate ofpercolation.9.5 M9.5 MOISTUREIN SOILHave you ever passed through afarmland during a hot summer day?Perhaps you noticed that the air abovethe land is shimmering. Why is it so?Try out this activity and find the answer.Activity 9.5Take a boiling tube. Put two spoonfullsof a soil sample in it. Heat it on a flame(Fig. 9.6) and observe it. Let us find outwhat happens upon heating.Do you see water drops any where?If yes, where did you find them?On heating, water in the soilevaporates, moves up and condenses onthe cooler inner walls of the upper partof the boiling tube.BurnerFig. 9.6 Removing moisture from the soilOn a hot summer day, the vapourcoming out of the soil reflect the sunlightand the air above the soil seems toshimmer.After heating the soil, take it out ofthe tube. Compare it with the soil whichhas not been heated. Note the differencebetween the two.9.6 ABSORPTIONOF WATERBY SOILDo all the soils absorb water to the sameextent? Let us find out.Activity 9.6Take a plastic funnel. Take a filter paper(or a piece of newspaper sheet), fold andplace it as shown in the figure. Weigh50g of dry, powdered soil and pour itinto the funnel. Measure a certainamount of water in a measuring cylinderand pour it drop by drop on the soil.You can use a dropper for this purpose.Do not let all the water fall at one spot.101SOIL101

www.GOALias.blogspot.comDropperFilter paperFig. 9.7 Absorption of water in the soilFunnelBeakerPour water all over the soil. Keep pouringwater till it starts dripping. Subtract theamount of water left in the measuringcylinder from the amount you startedwith. This is the amount of waterretained by the soil. Record your resultsin your notebook in the followingmanner:Weight of soil = 50gInitial volume of water in themeasuring cylinder = U mLFinal volume of water in themeasuring cylinder = V mLVolume of water absorbed by the soil= (U – V) mLWeight of water absorbed by the soil= (U – V) g(1 mL of water has weight equal to 1 g)percentage of water absorbed(U - V)= 10050Repeat this activity with different soilsamples. Would you get the same resultsfor all the samples? Discuss the resultswith your friends and answer thefollowing question:• Which soil would have the highestpercolation rate?• Which soil would have the lowestpercolation rate?• Boojho heard from his neighbourerthat 8–10 days after the rain, the levelof water in a pond or well rises. Whichtype of soil will allow water to reacha well faster and in greater amount?• Which type of soil retains the highestamount of water and which retainsthe least?• Can you suggest any method to letmore rain water percolate and reachthe water underground?9.7 S9.7 SOILAND CROPSDifferent types of soils are found indifferent parts of India. In some partsthere is clayey soil, in some parts thereis loamy soil while in some other partsthere is sandy soil.Soil is affected by wind, rainfall,temperature, light and humidity. Theseare some important climatic factorswhich affect the soil profile and bringchanges in the soil structure. TheGram (g) and kilogram (kg) are actually units of mass. A mass of 1 gram weighs 1 gram weight,and a mass of 1 kilogram weighs 1 kilogram weight. However, in daily life, and in commerce andindustry, the distinction between gram and gram weight is generally omitted.102SCIENCE

www.GOALias.blogspot.comclimatic factors, as well as thecomponents of soil, determine thevarious types of vegetation and cropsthat might grow in any region.Clayey and loamy soils are bothsuitable for growing cereals like wheat,and gram. Such soils are good atretaining water. For paddy, soils richin clay and organic matter andhaving a good capacity to retain waterare ideal. For lentils (masoor) and otherpulses, loamy soils, which drain watereasily, are required. For cotton, sandyloamor loam, which drain water easilyA case studyJohn, Rashida and Radha went to Leeladhar Dada and Sontosh Malviya ofSohagpur in Madhya Pradesh. Leeladhar Dada was preparing the soil to makeitems like surahi, matki, kalla (earthen frying pan) etc. The following is theconversation they all had with Leeladhar Dada:– Where was the soil obtained from?Dada–We brought the black soil from a piece of barren land.– How is the soil prepared?Dada–Dry soil will be placed in a large tank and would be cleaned of pebbles etc.After removing these things the soil will be soaked for around 8 hours.This soil would be kneaded after mixing horse dung. The kneaded soilwould be placed on the wheel and given appropriate shape. The final shapeis given with hands. The items are coloured after three days of drying. Allthe items are baked at high temperature after drying in the air.– Why is the horse dung mixed in soil?Dada–Burnt horse dung helps open up the pores in the soil. So that water couldpercolate out of the matkas and surahis, evaporate and cools the waterinside. You know Sohagpuri surahis and matkas are famous in far offplaces like Jabalpur, Nagpur, Allahabad, etc.Fig. 9.8 Making pots103SOIL103

www.GOALias.blogspot.comand can hold plenty of air, are moresuitable.Crops such as wheat are grown inthe fine clayey soils, because they arerich in humus and are very fertile. Findfrom your teachers, parents and farmersthe type of soils and crops grown in yourarea. Enter the data in the followingTable 9.2:Which kind of soil would be mostsuitable for planting rice? Soil with ahigher or lower rate of percolation?Table 9.2S. No. Type of soilCrop grown1. Clayey Wheat …………2.3.KeywordsClayeyHumusLoamyPercolationMoistureSandyWater retentionWhat is the differencebetween rate of percolation andthe amount of water retained?Boojho, you seem to haveforgotten what you readearlier. Go and reread thelesson again and you will findthe answer.Soil erosionThe removal of land surface by water,wind or ice is known as erosion. Plantroots firmly bind the soil. In theabsence of plants, soil becomes loose.So it can be moved by wind and flowingwater. Erosion of soil is more severein areas of little or no surfacevegetation, such as desert or barelands. So, cutting of trees anddeforestation should be prevented andeffort should be made to increase thegreen areas.What you have learnt• Soil is important for life on the earth.• Soil profile is a section through different layers of the soil, Various layersare called horizons.• Soil is of different types: clayey, loamy and sandy.• Percolation rate of water is different in different types of soil. It is highestin the sandy soil and least in the clayey soil.• Different types of soils are used to cultivate different types of crops. Clayand loam are suitable for growing wheat, gram and paddy. Cotton isgrown in sandy loam soil.104SCIENCE

www.GOALias.blogspot.com• Soil holds water in it, which is called soil moisture. The capacity of a soilto hold water is important for various crops.• Clayey soil is used to make pots, toys and statues.ExercisesTick the most suitable answer in questions 1 and 2.1. In addition to the rock particles, the soil contains(i)(ii)(iii)(iv)air and waterwater and plantsminerals, organic matter, air and waterwater, air and plants2. The water holding capacity is the highest in(i)(ii)(iii)(iv)sandy soilclayey soilloamy soilmixture of sand and loam3. Match the items in Column I with those in Column II:Column IColumn II(i) A home for living organisms (a) Large particles(ii) Upper layer of the soil (b) All kinds of soil(iii) Sandy soil (c) Dark in colour(iv) Middle layer of the soil (d) Small particles andpacked tight(v) Clayey soil (e) Lesser amount of humus4. Explain how soil is formed.5. How is clayey soil useful for crops?6. List the differences between clayey soil and sandy soil.7. Sketch the cross section of soil and label the various layers.8. Razia conducted an experiment in the field related to the rate ofpercolation. She observed that it took 40 min for 200 mL of water topercolate through the soil sample. Calculate the rate of percolation.105SOIL105

www.GOALias.blogspot.com9. Explain how soil pollution and soil erosion could be prevented.10. Solve the following crossword puzzle with the clues given:Across2. Plantation prevents it.5. Use should be banned to avoid soil pollution.6. Type of soil used for making pottery.7. Living organism in the soil.Down1. In desert soil erosion occurs through.3. Clay and loam are suitable for cereals like.4. This type of soil can hold very little water.5. Collective name for layers of soil.Extended Learning — Activities and Projects1. Boojho would like to know the difference between raw and baked soil?Investigate how the soil from which matkas are made is different fromthe soil used to make statues.106SCIENCE

www.GOALias.blogspot.com2. Paheli is worried. She could see a brick kiln from her house. Brickswere being made there. There was so much smoke coming out of thekiln. She was told that the best quality of clay is required for makingpottery, statues and bricks. She has seen truck loads of bricks beingtaken away for construction of buildings. At this rate, she fears, no soilwill be left. Are her fears justified? Discuss this problem with yourparents, teachers and other experts of your area and prepare a report.3. Try to find out the moisture content of a soil sample. One method isgiven here.Activity: Take 100g soil. (Take help from any shopkeepers to weighthe soil.) Place it on a newspaper in the sun and allow it to dry for twohours. This activity is best done in the afternoon. Take care that thesoil does not spill outside the newspaper. After drying it, weigh the soilagain. The difference in the weight of the soil before and after dryinggives you the amount of moisture contained in 100 g of soil. This iscalled the percentage moisture content.Suppose your sample of soil loses 10 g on drying. ThenPer cent of moisture in soil =In this examplePer cent of moisture in soil10×10010010%wt. of moisture (g)Original wt. of soil sample (g) ×100Did you know?Rivers of north India, which flow from Himalayas, bring a variety ofmaterials including silt, clay, sand and gravel. They deposit theirmaterials called alluvial soil, in the planes of north India. This soil is veryfertile and supports nearby half the population of India.107SOIL107

www.GOALias.blogspot.com1010 Respiration in OrganismsOne day Boojho was eagerlywaiting to meet hisgrandparents who were comingto the town after a year. He was in a realhurry as he wanted to receive them at thebus-stop. He ran fast and reached thebus-stop in a few minutes. He wasbreathing rapidly. His grandmother askedhim why he was breathing so fast. Boojhotold her that he came running all the way.But the question got stuck in his mind.He wondered why running makes aperson breathe faster. The answer toBoojho’s question lies in understandingwhy we breathe. Breathing is a part ofrespiration. Let us learn about respiration.10.1 WHYHY DO WE RESPIREESPIRE?In Chapter 2 you learnt that allorganisms are made of smallmicroscopic units called cells. A cell isthe smallest structural and functionalunit of an organism. Each cell of anorganism performs certain functionssuch as nutrition, transport, excretionand reproduction. To perform thesefunctions, the cell needs energy. Evenwhen we are eating, sleeping or readingwe require energy. But, where does thisenergy come from? Can you say whyyour parents insist that you should eatregularly? The food has stored energy,which is released during respiration.Therefore, all living organisms respireto get energy from food. Duringbreathing, we breathe in air. You knowthat air contains oxygen. We breathe outair which is rich in carbon dioxide. Theair we breathe in is transported to allparts of the body and ultimately to eachcell. In the cells, oxygen in the air helpsin the breakdown of food. The processof breakdown of food in the cell with therelease of energy is called cellularrespiration. Cellular respiration takesplace in the cells of all organisms.In the cell, the food (glucose) is brokendown into carbon dioxide and water usingoxygen. When breakdown of glucoseoccurs with the use of oxygen it is calledaerobic respiration. Food can also bebroken down, without using oxygen. Thisis called anaerobicrespiration.Breakdown of food releases energy.With the use of oxygenGlucosecarbon dioxide + water + energyYou should know that there are someorganisms such as yeast that can survivein the absence of air. They are calledanaerobes. They get energy throughanaerobic respiration. In the absence ofoxygen, glucose breaks down into alcoholand carbon dioxide, as given below:Without the use of oxygenGlucosealcohol + carbon dioxide + energy108SCIENCE

www.GOALias.blogspot.comYeasts are single-celled organisms.They respire anaerobically and duringthis process yield alcohol. They are,therefore, used to make wine and beer.Our muscle cells can also respireanaerobically, but only for a short time,when there is a temporary deficiency ofoxygen. During heavy exercise, fastrunning (Fig. 10.1), cycling, walking formany hours or heavy weight lifting, thedemand for energy is high. But thesupply of oxygen to produce the energyis limited. Then anaerobic respirationtakes places in the muscle cells to fulfilthe demand of energy:Glucose(in muscle)lactic acid + energyin the absence of oxygenFig. 10.1 During exercise, some muscles mayrespire anaerobicallyHave you ever wondered why you getmuscle cramps after heavy exercise? Thecramps occur when muscle cells respireanaerobically. The partial breakdown ofglucose produces lactic acid. Theaccumulation of lactic acid causes musclecramps. We get relief from cramps after ahot water bath or a massage. Can youguess why it is so? Hot water bath ormassage improves circulation of blood.As a result, the supply of oxygen to themuscle cells increases. The increase inthe supply of oxygen results in thecomplete breakdown of lactic acid intocarbon dioxide and water.10.2 BREATHINGActivity 10.1CAUTIONDo this activity under the supervisionof your teacher.Close your nostrils and mouthtightly and look at a watch. What didyou feel after some time? How long wereyou able to keep both of them closed?Note down the time for which you couldhold your breath (Fig. 10.2).So, now you know that you cannotsurvive for long without breathing.You must have seen the movementof the abdomen of dogs, cats and cows,as they breathe. Breathing means takingin air rich in oxygen and giving out airrich in carbon dioxide with the help ofrespiratory organs. The taking in of airrich in oxygen into the body is calledinhalation and giving out of air rich in109RESPIRATIONIN ORGANISMS109

www.GOALias.blogspot.comcarbon dioxide is known as exhalation.It is a continuous process which goeson all the time and throughout the lifeof an organism.The number of times a personbreathes in a minute is termed as thebreathing rate. Both inhalation andexhalation take place. A breath meansFig. 10.2 Holding breathBoojho noticed that when hereleased his breath after holdingit for some time, he had tobreathe heavily. Can you tellhim why it was so?one inhalation plus one exhalation.Would you like to find out yourbreathing rate? Do you want to knowwhether it is constant or it changesaccording to the requirement of oxygenby the body? Let us find out by doingthe following activity.Activity 10.2Generally we are not aware that we arebreathing. However, if you try you cancount your rate of breathing. Breathein and out normally. Find out how manytimes you breathe in and breathe outin a minute? Did you inhale the samenumber of times as you exhaled? Nowcount your breathing rate (number ofbreaths/minute) after brisk walk andafter running. Record your breathingrate as soon as you finish and also aftercomplete rest. Tabulate your findingsand compare your breathing rates underdifferent conditions with those of yourclassmates.From the above activity, you musthave realised that whenever a personneeds extra energy, he/she breathesfaster. As a result more oxygen isTable 10.1 Changes in breathing rate under different conditionsName of the classmateNormalBreathing rateAfter a briskAfter runningwalk for 10fast 100 mminutesAt restSelf110SCIENCE

www.GOALias.blogspot.comOn an average, an adult human beingat rest breathes in and out 15–18times in a minute. During heavyexercise, the breathing rate canincrease upto 25 times per minute.While we exercise, not only do webreathe fast, we also take deep breathsand thus inhale more oxygen.supplied to our cells. It speeds upthe breakdown of food and moreenergy is released. Does this explainwhy we feel hungry after a physicalactivity?When you feel drowsy, does yourbreathing rate slow down? Does yourbody receive sufficient oxygen?Activity 10.3Figure 10.3 shows the various activitiescarried out by a person during a normalFig. 10.3 Variation in the breathing rate duringdifferent activitiesPaheli wants to know whywe yawn when we aresleepy or drowsy.day. Can you say in which activity, therate of breathing will be the slowest andin which it will be the fastest? Assignnumbers to the pictures in the order ofincreasing rate of breathing accordingto your experience.10.3 HOWDO WE BREATHEREATHE?Let us now learn about the mechanismof breathing. Normally we take in airthrough our nostrils. When we inhaleair, it passes through our nostrils intothe nasal cavity. From the nasal cavity,the air reaches our lungs through thewindpipe. Lungs are present in thechest cavity (Fig. 10.4). This cavity issurrounded by ribs on the sides. A large,muscular sheet called diaphragm formsthe floor of the chest cavity (Fig. 10.4).Breathing involves the movement of thediaphragm and the rib cage.During inhalation, ribs move up andoutwards and diaphragm moves down.This movement increases space in ourchest cavity and air rushes into thelungs. The lungs get filled with air.During exhalation, ribs move down andinwards, while diaphragm moves up toits former position. This reduces the sizeof the chest cavity and air is pushed outof the lungs (Fig. 10.5). Thesemovements in our body can be felt111RESPIRATIONIN ORGANISMS111

www.GOALias.blogspot.comeasily. Take a deep breath. Keep yourpalm on the abdomen, feel themovement of abdomen. What do youfind?After having learnt that duringbreathing there are changes in the sizeof the chest cavity, children got involvedin the chest expansion competition.Smoking damages lungs. Smoking isalso linked to cancer. It must beavoided.Everyone was boasting that she/hecould expand it the maximum. Howabout doing this activity in the classwith your classmates?Nasal passagePharynxOral cavityTracheaLungsRibsDiaphragmFig 10.4 Human respiratory systemThe air around us has various types of unwanted particles, such as smoke, dust,pollens, etc. When we inhale, the particles get trapped in the hair present in ournasal cavity. However, sometimes these particles may get past the hair in thenasal cavity. Then they irritate the lining of the cavity, as a result of which wesneeze. Sneezing expels these foreign particles from the inhaled air and a dustfree,clean air enters our body.TAKE CARE: When you sneeze, you should cover your nose so that the foreignparticles you expel are not inhaled by other persons.112SCIENCE

www.GOALias.blogspot.comActivity 10.4Take a deep breath. Measure the sizeof the chest with a measuring tape(Fig. 10.6) and record your observationsin Table 10.2. Measure the size of thechest again when expanded andindicate which classmate shows themaximum expansion of the chest.We can understand the mechanismof breathing by a simple model.Activity 10.5Take a wide plastic bottle. Remove thebottom. Get a Y-shaped glass or plastictube. Make a hole in the lid so that thetube may pass through it. To the forkedend of the tube fix two deflated balloons.Introduce the tube into the bottle asshown in Fig. 10.7. Now cap the bottle.Seal it to make it airtight. To the openbase of the bottle tie a thin rubber orplastic sheet using a large rubber band.Air isdrawn inAir forced outRibs moveoutRibs movebackDiaphragmmoves downDiaphragmmoves back(a) Inhalation(b) ExhalationFig. 10.5 Mechanism of breathing in human beingsTable 10.2: Effect of breathing on the chest size of some classmatesName of theclassmateSize of the chest (cm)During inhalationDuring exhalationDifference in size113RESPIRATIONIN ORGANISMS113

www.GOALias.blogspot.comtest-tube. Insert a plastic straw throughthe hole in the lid in such a way that itdips in lime water. Now blow gentlythrough the straw a few times (Fig.10.8). Is there a change in theappearance of lime water? Can youexplain this change on the basis of whatyou learnt in Chapter 6?You are aware that air weinhale or exhale is a mixture ofgases. What do we exhale? Do weexhale only carbon dioxide or a mixtureof gases along with it? You must havealso observed that if you exhale on amirror, a film of moisture appears on itssurface. From where do these dropletscome?Fig. 10.6 Measuring chest sizeTo understand the expansion of thelungs, pull the rubber sheet from thebase downwards and watch the balloons.Next, push the rubber/plastic sheet upand observe the balloons. Did you seeany changes in the balloons?What do the balloons in this modelrepresent? What does the rubber sheetrepresent?Now, you should be able to explainthe mechanism of breathing.10.4 WHATDO WE BREATHEOUT ?Activity 10.6Take a slender, clean test tube or aglass/plastic bottle. Make a hole in itslid and fix it on the bottle. Pour somefreshly prepared lime water in theBoojho wants to know howmuch air a person can hold inthe lungs.PlasticbottleBalloonsRubersheetFig 10.7 Model to show mechanism ofbreathing114SCIENCE

www.GOALias.blogspot.comBoojho wants to know ifcockroaches, snails, fish,earthworms, ants and mosquitoesalso have lungs.StrawLime waterFig 10.8 Effect of exhaled air on lime waterThe percentage of oxygen and carbondioxide in inhaled and exhaled air.Inhaled airExhaled air21% oxygen 16.4% oxygenThese openings are called spiracles(Fig. 10.9). Insects have a network of airtubes called tracheae for gas exchange.Oxygen rich air rushes through spiraclesinto the tracheal tubes, diffuses into thebody tissue, and reaches every cell ofthe body. Similarly, carbon dioxide fromthe cells goes into the tracheal tubes andmoves out through spiracles. These airtubes or tracheae are found only ininsects and not in any other group ofanimals.TracheaeLungs0.04% carbondioxide4.4% carbondioxide10.5 B10.5 BREATHINGIN OTHERANIMALSAnimals such as elephants, lions, cows,goats, frogs, lizards, snakes, birds, havelungs in their chest cavities like thehuman beings.How do these organisms breathe? Dothey also have lungs like those of humanbeings? Let us find out.Cockroach: A cockroach has smallopenings on the sides of its body. Otherinsects also have similar openings.Fig.10.9 Tracheal systemEarthworm: Recall from Chapter 9 ofClass VI that earthworms breathethrough their skins. The skin of anearthworm feels moist and slimy ontouching. Gases can easily pass throughthem. Though frogs have pair of lungslike human beings, they can alsobreathe through their skin, which ismoist and slippery.115RESPIRATIONIN ORGANISMS115

www.GOALias.blogspot.comBoojho has seen in televisionprogrammes that whales anddolphins often come up to thewater surface. They even releasea fountain of water sometimeswhile moving upwards. Why dothey do so?dioxide. In the cells oxygen is used tobreak down glucose into carbon dioxideand water as in other organisms. Inplants each part can independently takein oxygen from the air and give outcarbon dioxide. You have already learntin Chapter 1 that the leaves of the plantshave tiny pores called stomata forexchange of oxygen and carbon dioxide.10.6 B10.6 BREATHINGUNDER WATERCan we survive in water? There are manyorganisms which live in water. How dothey breathe under water?You have studied in Class VI thatgills in fish help them to use oxygendissolved in water. Gills are projectionsof the skin. You may wonder how gillshelp in breathing. Gills are well suppliedwith blood vessels (Fig. 10.10) forexchange of gases.GillsPaheli wants to know whetherroots, which are undergroundalso take in oxygen? If so, how?Like all other living cells of theplants, the root cells also needoxygen to generate energy. Roots takeup air from the air spaces presentbetween the soil particles (Fig. 10.11).Soil particlesRoot hair10.7Fig. 10.10 Breathing organs in fish10.7 DO PLANTSALSO RESPIREESPIRE?Like other living organisms, plants alsorespire for their survival as you havelearnt in Class VI. They also take inoxygen from the air and give out carbonAir spaceFig. 10.11 Roots absorb air from the soil116SCIENCE

www.GOALias.blogspot.comCan you guess what would happenif a potted plant is overwatered?In this chapter you learntthat respiration is a vital biologicalprocess. All living organisms needto respire to get the energy neededfor their survival.KeywordsAerobic respirationAnaerobic respirationBreathing rateCellular respirationDiaphragmExhalationGillsInhalationSpiraclesTracheaeWhat you have learnt• Respiration is essential for survival of living organisms. It releases energyfrom the food.• The oxygen we inhale is used to breakdown glucose into carbon dioxideand water. Energy is released in the process.• The breakdown of glucose occurs in the cells of an organism (cellularrespiration).• If the food is broken down with the use of oxygen, it is called aerobicrespiration. If the breakdown occurs without the use of oxygen, therespiration is called anaerobic respiration.• During heavy exercise when the supply of oxygen to our muscle cells isinsufficient, food breakdown is by anaerobic respiration.• Breathing is a part of the process of respiration during which anorganism takes in the oxygen-rich air and gives out air rich in carbondioxide. The respiratory organs for the exchange of gases vary in differentorganisms.• During inhalation, our lungs expand and then come back to the originalstate as the air moves out during exhalation.• Increased physical activity enhances the rate of breathing.• In animals like cow, buffalo, dog and cat the respiratory organs and theprocess of breathing are similar to those in humans.• In earthworm, the exchange of gases occurs through the moist skin. Infishes it takes place through gills and in insects through the tracheae.• In a plant the roots take in air present in the soil. Leaves have tiny porescalled stomata through which they exchange gases. The breakdown ofglucose in the plant cells is similar to that in other living beings.117RESPIRATIONIN ORGANISMS117

www.GOALias.blogspot.comExercises1. Why does an athlete breathe faster and deeper than usual afterfinishing the race?2. List the similarities and differences between aerobic and anaerobicrespiration.3. Why do we often sneeze when we inhale a lot of dust-laden air?4. Take three test-tubes. Fill th of each with water. Label them A, B andC. Keep a snail in test-tube A, a water plant in test-tube B and in C,keep snail and plant both. Which test-tube would have the highestconcentration of CO 2?5. Tick the correct answer:(a)(b)(c)(d)In cockroaches, air enters the body through(i) lungs (ii) gills(iii) spiracles (iv) skinDuring heavy exercise, we get cramps in the legs due to the accumulation of(i) carbon dioxide (ii) lactic acid(iii) alcohol (iv) waterNormal range of breathing rate per minute in an average adultperson at rest is:(i) 9–12 (ii) 15–18(iii) 21–24 (iv) 30–33During exhalation, the ribs(i) move outwards (ii) move downwards(iii) move upwards (iv) do not move at all6. Match the items in Column I with those in Column II:Column IColumn II(a) Yeast (i) Earthworm(b) Diaphragm (ii) Gills(c) Skin (iii) Alcohol(d) Leaves (iv) Chest cavity(e) Fish (v) Stomata(f) Frog (vi) Lungs and skin(vii)Tracheae118SCIENCE

www.GOALias.blogspot.com7. Mark ‘T’ if the statement is true and ‘F’ if it is false:(i)During heavy exercise the breathing rate of a person slowsdown. (T/F)(ii) Plants carry out photosynthesis only during the day andrespiration only at night. (T/F)(iii) Frogs breathe through their skins as well as their lungs. (T/F)(iv) The fishes have lungs for respiration. (T/F)(v) The size of the chest cavity increases during inhalation. (T/F)9. Given below is a square of letters in which are hidden different wordsrelated to respiration in organisms. These words may be present in anydirection — upwards, downwards, or along the diagonals. Find the wordsfor your respiratory system. Clues about those words are given belowthe square.S V M P L U N G SC Z G Q W X N T LR M A T I D O T CI Y R X Y M S R AB R H I A N T A YS T P T B Z R C EM I A M T S I H AS P I R A C L E SN E D K J N S A T(i) The air tubes of insects(ii) Skeletal structures surrounding chest cavity(iii) Muscular floor of chest cavity(iv) Tiny pores on the surface of leaf(v) Small openings on the sides of the body of an insect(vi) The respiratory organs of human beings(vii) The openings through which we inhale(viii) An anaerobic organism(ix) An organism with tracheal system10. The mountaineers carry oxygen with them because:(a) At an altitude of more than 5 km there is no air.119RESPIRATIONIN ORGANISMS119

www.GOALias.blogspot.com(b)(c)(d)The amount of air available to a person is less than that availableon the ground.The temperature of air is higher than that on the ground.The pressure of air is higher than that on the ground.Extended Learning — Activities and Projects1. Observe fish in an aquarium. You will find flap like structures on bothsides of their heads. These are flaps which cover the gills. These flapsopen and close alternately. On the basis of these observations, explainthe process of respiration in the fish.2. Visit a local doctor. Learn about the harmful effects of smoking. You canalso collect material on this topic from other sources. You can seek helpof your teacher or parents. Find out the percentage of people of yourarea who smoke. If you have a smoker in your family, confront him withthe material that you have collected.3. Visit a doctor. Find out about artificial respiration. Ask the doctor:(a)(b)(c)When does a person need artificial respiration?Does the person need to be kept on artificial respiration temporarily or permanently?From where can the person get supply of oxygen for artificial respiration?4. Measure the breathing rate of the members of your family and some ofyour friends. Investigate:(c) If the breathing rate of children is different from that of adults.(d) If the breathing rate of males is different from that of females.If there is a difference in any of these cases, try to find the reason.You can read more on the following website:www.health.howstuffworks.com/adam-200142.htmDid you know?For us oxygen is essential, but for those organisms which do not use it,oxygen is toxic. In fact, our white blood cells use oxygen to kill invadingbacteria. Even for humans, it may be dangerous to breathe pure oxygenfor long.120SCIENCE

www.GOALias.blogspot.com1111 Transportation in Animalsand PlantsYou have learnt earlier that allorganisms need food, water andoxygen for survival. They need totransport all these to various parts oftheir body. Further, animals need totransport wastes to parts from wherethey can be removed. Have youwondered how all this is achieved? Lookat Fig. 11.1. Do you see the heart andthe blood vessels? They function totransport substances and together formthe circulatory system. In this chapteryou shall learn about transport ofsubstances in plants and animals.11.1 CIRCULATORYSYSTEMBloodWhat happens when you get a cut onyour body? Blood flows out. But whatis blood? Blood is the fluid whichflows in blood vessels. It transportssubstances like digested food from thesmall intestine to the other parts of thebody. It carries oxygen from the lungsto the cells of the body. It also transportswaste for removal from the body.How does the blood carry varioussubstances? Blood is a liquid, which hascells of various kinds suspended in it.HeartVeinArteryWhy is the colour ofblood red?Fig. 11.1 Circulatory system(Arteries are shown in red colour and vein in blue)

www.GOALias.blogspot.comThe fluid part of the blood is calledplasma.One type of cells are the red bloodcells (RBC) which contain a red pigmentcalled haemoglobin. Haemoglobin bindwith oxygen and transports it to all theparts of the body and ultimately to allthe cells. It will be difficult to provideoxygen efficiently to all the cells ofthe body without haemoglobin. Thepresence of haemoglobin makes bloodappear red.The blood also has white blood cells(WBC) which fight against germs thatmay enter our body.Boojho fell down while playing agame and his knee got injured. Bloodwas coming out from the cut. After sometime, he noticed that bleeding hadstopped and a dark red clot had pluggedthe cut. Boojho was puzzled about this.The clot is formed because of thepresence of another type of cells in theblood, called platelets.Blood vesselsThere are different types of blood vesselsin the body. You know that duringinhalation a fresh supply of oxygen fillsthe lungs. Oxygen has to be transportedto the rest of the body.Also, the blood picks up the wastematerials including carbon dioxide fromthe cells. This blood has to go back tothe heart for transport to the lungs forremoval of carbon dioxide as you havelearnt in Chapter 10. So, two types ofblood vessels are present in the arteriesand veins of the body. (Fig. 11.1)Arteries carry oxygen-rich bloodfrom the heart to all parts of the body.Since the blood flow is rapid and at ahigh pressure, the arteries have thickelastic walls.Let us perform an activity to studythe flow of blood through arteries.Activity 11.1Place the middle and index finger ofyour right hand on the inner side of yourleft wrist (Fig. 11.2). Can you feel somethrobbing movements? Why do youthink there is throbbing? Thisthrobbing is called the pulse and it isdue to the blood flowing in the arteries.Count the number of pulse beats in oneminute.How many pulse beats could youcount? The number of beats per minuteis called the pulse rate. A restingperson, usually has a pulse rate between72 and 80 beats per minute. Find otherplaces in your body where you can feelthe pulse.Record your own pulse beats perminute and those of your classmates.Fig. 11.2 Pulse in the wrist122SCIENCE

www.GOALias.blogspot.comCompare the values you obtained andinsert them in Table 11.1.Table 11.1 Pulse rateS. No. Name1.2.3.4.5.Pulse per minuteVeins are the vessels which carrycarbon dioxide-rich blood from all partsof the body back to the heart. The veinshave thin walls. There are valves presentin veins which allow blood to flow onlytowards the heart.PulmonaryarteryVeinLungsHeartCapillariesPulmonaryveinArteryFig. 11.3 Schematic diagram of circulationI am confused! I have learntthat an artery alwayscarries oxygen-rich blood.Paheli explained that thepulmonary artery carries bloodfrom the heart, so it is called anartery and not a vein. It carriescarbon dioxide-rich blood to thelungs. Pulmonary vein carriesoxygen-rich blood from thelungs to the heart.Refer to Fig. 11.3. Do you see thearteries divide into smaller vessels. Onreaching the tissues, they divide furtherinto extremely thin tubes calledcapillaries. The capillaries join up toform veins which empty into the heart.HeartThe heart is an organ which beatscontinuously to act as a pump for thetransport of blood, which carries othersubstances with it.Imagine a pump working foryears without stopping! Absolutelyimpossible. Yet our heart works like apump non-stop. Let us now learn aboutthe heart.The heart is located in the chestcavity with its lower tip slightly tiltedtowards the left (Fig. 11.1). Hold yourfingers inwards on your palm. That123TRANSPORTATIONIN ANIMALSAND PLANTS123

www.GOALias.blogspot.commakes your fist. Your heart is roughlythe size of your fist.What will happen if the blood rich inoxygen and the blood rich in carbondioxide mix with each other? To avoidthis from happening, the heart has fourchambers. The two upper chambers arecalled the atria (singular: atrium) andthe two lower chambers are called theventricles (Fig. 11.4). The partitionbetween the chambers helps to avoidPulmonary arteryAortaPulmonary veinRight atriumLeft atriumPartition completelyseparating the twohalvesLeft ventricleRight ventricleFig. 11.4 Sections of human heartPaheli wonders which side ofthe heart will have oxygen-richblood and which side will havecarbon dioxide-rich blood.mixing up of blood rich in oxygen withthe blood rich in carbon dioxide.To understand the functioning of thecirculatory system, start from the rightside of the heart in Fig. 11.3 and followthe arrows. These arrows show thedirection of the blood flow from the heart124SCIENCE

www.GOALias.blogspot.comto the lungs and back to the heart fromwhere it is pumped to the rest of thebody.HeartbeatThe walls of the chambers of the heartare made up of muscles. These musclescontract and relax rhythmically. Thisrhythmic contraction followed by itsrelaxation constitute a heartbeat.Remember that heartbeats continueevery moment of our life. If you placeyour hand on the left side of your chest,you can feel your heartbeat. The doctorfeels your heartbeats with the help ofan instrument called a stethoscope.A doctor uses the stethoscope as adevice to amplify the sound of the heart.It consists of a chest piece that carries asensitive diaphragm, two ear pieces anda tube joining the parts. Doctors canget clues about the condition of yourheart by listening through astethoscope.Let us construct a model of astethoscope with the materials that areavailable around us.Activity 11.2Take a small funnel of 6–7 cm indiameter. Fix a rubber tube (50 cm long)tightly on the stem of the funnel. Stretcha rubber sheet (or a balloon) on themouth of the funnel and fix it tightlywith a rubber band. Put the open endof the tube on one of your ears. Place(a) Stethoscope(b) Model ofstethoscopeFig. 11.5 Instrument to hear heartbeatTable 11.2 Heartbeat and pulse rateName of studentWhile resting After running (4 – 5 minutes)HeartbeatPulse rateHeartbeatPulse rate125TRANSPORTATIONIN ANIMALSAND PLANTS125

www.GOALias.blogspot.comthe mouth of the funnel on your chestnear the heart. Now try to listencarefully. Do you hear a regularthumping sound ? The sound is that ofheartbeats. How many times did yourheartbeat in a minute ? Count againafter running for 4–5 minutes. Compareyour observations.Record your own pulse rate andheartbeat and that of your friends whileresting and after running and record inTable 11.2. Do you find any relationshipbetween your heartbeat and pulse rate?Each heart beat generates one pulse inthe arteries and the pulse rate perminute indicates the rate of heartbeat.The rhythmic beating of the variouschambers of the heart maintaincirculation of blood and transport ofsubstances to the different parts of thebody.Boojho wonders if sponges andhydra also have blood? Animals suchas sponges and Hydra do not posses anycirculatory system. The water in whichthey live brings food and oxygen as itThe English physician, William Harvey(A.D.1578–1657), discovered thecirculation of blood. The currentopinion in those days was that bloodoscillates in the vessels of the body.For his views, Harvey was ridiculedand was called “circulator”. He lostmost of his patients. However, beforehe died, Harvey’s idea aboutcirculation was generally accepted asa biological fact.enters their bodies. The water carriesaway waste materials and carbon dioxideas it moves out. Thus, these animals donot need a circulatory fluid like theblood.Let us now learn about the removalof waste other than carbon dioxide.11.2 EXCRETIONIN ANIMALSRecall how carbon dioxide is removedas waste from the body through thelungs during exhalation. Also recall thatthe undigested food is removed duringegestion. Let us now find out how theother waste materials are removed fromthe body. You may wonder where theseunwanted materials come from!When our cells perform theirfunctions, certain waste products arereleased. These are toxic and hence needto be removed from the body. Theprocess of removal of wastes producedin the cells of the living organisms iscalled excretion. The parts involved inexcretion forms the excretory system.Excretory system in humansThe waste which is present in the bloodhas to be removed from the body. Howcan this be done? A mechanism to filterthe blood is required. This is done bythe blood capillaries in the kidneys.When the blood reaches the two kidneys,it contains both useful and harmfulsubstances. The useful substances areabsorbed back into the blood. Thewastes dissolved in water are removedas urine. From the kidneys, the urinegoes into the urinary bladder through126SCIENCE

www.GOALias.blogspot.comKidneyUretercontains water and salts. Boojho hasseen that sometimes in summer, whitepatches are formed on our clothes,especially in areas like underarms.These marks are left by salts present inthe sweat.Does sweat serve any other function?We know that the water kept in anearthen pot (matka) is cooler. This isbecause the water evaporates from thepores of the pot, which causes cooling.Urinary bladderUrethraUrinary openingFig. 11.6 Human excretory systemtube-like ureters. It is stored in thebladder and is passed out through theurinary opening at the end of amuscular tube called urethra (Fig. 11.6).The kindeys, ureters, bladder andurethra form the excretory system.An adult human being normallypasses about 1–1.8 L of urine in 24hours, and the urine consists of 95%water, 2.5 % urea and 2.5% other wasteproducts.We have all experienced that we sweaton a hot summer day. The sweatPaheli wants to knowwhether other animals alsourinate?The way in which waste chemicals areremoved from the body of the animaldepends on the availability of water.Aquatic animals like fishes, excrete cellwaste in gaseous form (ammonia)which directly dissolves in water. Someland animals like birds, lizards,snakes excrete a semi-solid, whitecoloured compound (uric acid). Themajor excretory product in humansis urea.Sometimes a person’s kidneys maystop working due to infection orinjury. As a result of kidney failure,waste products start accumulating inthe blood. Such persons cannotsurvive unless their blood is filteredperiodically through an artificialkidney. This process is called dialysis.127TRANSPORTATIONIN ANIMALSAND PLANTS127

www.GOALias.blogspot.comSimilarly, when we sweat, it helps to coolour body.11.3 TRANSPORTOF SUBSTANCESINPLANTSIn Chapter 1 you learnt that plants takewater and mineral nutrients from the soilthrough the roots and transport it to theleaves. The leaves prepare food for theplant, using water and carbon dioxideduring photosynthesis. You also learnt inChapter 10 that food is the source ofenergy and every cell of an organism getsenergy by the breakdown of glucose. Thecells use this energy to carry out vitalactivities of life. Therefore food must bemade available to every cell of anorganism. Have you ever wondered howwater and nutrients absorbed by theroot are transported to the leaves? Howis the food prepared by the leaves carriedto the parts which cannot make food?Transport of water andmineralsPlants absorb water and minerals bythe roots. The roots have root hair.The root hair increase the surface areaof the root for the obsorption of waterand mineral nutrients dissolved inwater. The root hair is in contact withthe water present between the soilparticles [Fig. 11.7 (a)].Can you guess how water movesfrom the root to the leaves? What kindof transport system is present in plants?Boojho thinks that plantsmay have pipes to transportwater to the entire plant likewe have in our homes for thesupply of water.Root hair(b)Xylem vessels(a)Fig. 11.7 Transport of water and minerals in(a) a section of root, (b) a tree128SCIENCE

www.GOALias.blogspot.comWell, Boojho is right. Plants havepipe-like vessels to transport water andnutrients from the soil. The vessels aremade of special cells, forming thevascular tissue. A tissue is a group ofcells that perform specialised functionin an organism. The vascular tissue forthe transport of water and nutrients in theplant is called the xylem [Fig. 11.7 (a)].The xylem forms a continuousnetwork of channels that connects rootsto the leaves through the stem andbranches and thus transports water tothe entire plant [Fig. 11.7 (b)].Paheli says her mother putsladyfinger and other vegetables inwater if they are somewhat dry.She wants to know how waterenters into them.You know that leaves synthesisefood. The food has to be transported toall parts of the plant. This is done bythe vascular tissue called the phloem.Thus, xylem and phloem transportsubstances in plants.Activity 11.3Take a large potato and peel off its outerskin. Cut one of its ends to make thebase flat. Now make a deep and hollowcavity on the opposite side. Fill half ofthe cavity with sugar solution and markthe level by inserting a pin in the wallof the potato (Fig. 11.8). Put the potatoPotatoSugarsolutionPinWaterFig. 11.8 Transportation of water through cellsinto a dish containing a small amountof water. Make sure that the level of wateris below the level of the pin. Allow theapparatus to stand for a few hours.You would find an increase in thelevel of sugar solution. How did waterget inside the potato? For very shortdistances water can move from one cellto another. In the same way waterreaches xylem vessels of the root fromthe soil [Fig. 11.7 (a)].TranspirationIn Class VI you learnt that plants releasea lot of water by the process oftranspiration.Plants absorb mineral nutrients andwater from the soil. Not all the waterabsorbed is utilised by the plant. Thewater evaporates through the stomatapresent on the surface of the leaves byBoojho wants to know whyplants absorb a large quantityof water from the soil, then giveit off by transpiration!129TRANSPORTATIONIN ANIMALSAND PLANTS129

www.GOALias.blogspot.comthe process of transpiration. Theevaporation of water from leavesgenerates a suction pull (the samethat you produce when you suckwater through a straw) which canpull water to great heights in thetall trees. Transpiration also coolsthe plant.KeywordsAmmoniaArteryBloodBlood vesselsCapillaryCirculatory systemDialysisExcretionExcretory systemHaemoglobinHeart beatKidneysPhloemPlasmaPlateletsPulseRed blood cellRoot hairStethoscopeSweatTissueUreaUreterUrethraUric acidUrinary bladderVeinWhite blood cellXylemWhat you have learnt• In most animals the blood that circulates in the body distributes foodand oxygen to different cells of the body. It also carries waste products todifferent parts of the body for excretion.• Circulatory system consists of the heart and blood vessels.• In humans, blood flows through arteries and veins and the heart actsas a pumping organ.• Blood consists of plasma, RBC, WBC and platelets. Blood is red due tothe presence of a red pigment, haemoglobin.• The human heart beats about 70–80 times per minute in an adultperson. This is called heart rate.• Arteries carry blood from the heart to all parts of the body.• Veins carry blood from all parts of the body back to the heart.• Removal of waste products from the body is called excretion.• Excretory system of humans consists of two kidneys, two ureters, aurinary bladder, and urethra.• Salts and urea are removed along with water as sweat.130SCIENCE

www.GOALias.blogspot.com• Fish excrete waste substances which directly dissolve in water.• Birds, insects and lizard excrete uric acid in semi-solid form.• Water and mineral nutrients are absorbed by roots from the soil.• Nutrients are transported along with water to the entire plant via thevascular tissue called xylem.• The vascular tissue for the transport of food to the various parts of theplant is phloem.• A lot of water is lost by plants in the form of vapour through stomataduring transpiration.• Transpiration generates a force which pulls up water absorbed by theroots from the soil, to reach the stem and leaves.Exercises1. Match structures given in Column I with functions given in Column II.Column IColumn II(i) Stomata (a) Absorption of water(ii) Xylem (b) Transpiration(iii) Root hairs (c) Transport of food(iv) Phloem (d) Transport of water(e) Synthesis of carbohydrates2. Fill in the blanks.(i) The blood from the heart is transported to all parts of the body bythe .(ii) Haemoglobin is present in cells.(iii) Arteries and veins are joined by a network of .(iv) The rhythmic expansion and contraction of the heart is called.(v) The main excretory product in human beings is .(vi) Sweat contains water and .(vii) Kidneys eliminate the waste materials in the liquid form called.(viii) Water reaches great heights in the trees because of suction pullcaused by .131TRANSPORTATIONIN ANIMALSAND PLANTS131

www.GOALias.blogspot.com3. Choose the correct options:(a)In plants, water is transported through(i) Xylem (ii) Phloem(iii) Stomata (iv) Root hair(b) Water absorption through roots can be increased by keeping theplants(i) in the shade(ii) in dim light(iii) under the fan(iv) covered with a polythene bag4. Why is transport of materials necessary in a plant or in an animal?Explain.5. What will happen if there are no platelets in the blood?6. What are stomata? Give two functions of stomata.7. Does transpiration serve any useful function in the plants? Explain.8. What are the components of blood?9. Why is blood needed by all the parts of a body?10. What makes the blood look red?11. Describe the function of the heart.12. Why is it necessary to excrete waste products?13. Draw a diagram of the human excretory system and label the variousparts.Extended Learning — Activities and Projects1. Find out about blood groups and their importance.2. When a person suffers from chest pain, the doctor immediately takesan ECG. Visit a doctor and get information about ECG. You may evenlook up an encyclopaedia or the internet.You can read more on the following website:www.health.howstuffworks.com/adam-200142.htmDid you know?There is no substitute for blood. If people lose blood from surgery or injuryor if their bodies cannot produce enough blood, there is only one way toget it — through transfusion of blood donated by volunteers. Blood isusually in short supply. Donating blood does not decrease the strength ofthe donors.132SCIENCE

www.GOALias.blogspot.com1212 Reproduction in PlantsTo produce its kind is acharacteristic of all livingorganisms. You have alreadylearnt this in Class VI. The productionof new individuals from their parents isknown as reproduction. But, how doplants reproduce? There are differentmodes of reproduction in plants whichwe shall learn in this chapter.12.1 M12.1 MODESOF REPRODUCTIONIn Class VI you learnt about differentparts of a flowering plant. Try to list thevarious parts of a plant and write thefunctions of each. Most plants haveroots, stems and leaves. These are calledthe vegetative parts of a plant. After acertain period of growth, most plantsbear flowers. You may have seen themango trees flowering in spring. It isthese flowers that give rise to juicymango fruit we enjoy in summer. We eatthe fruits and usually discard the seeds.Seeds germinate and form new plants.So, what is the function of flowers inplants? The flowers perform the functionof reproduction in plants. Flowers arethe reproductive parts of a plant. Aflower may have either the male part orthe female part or both male and femaleparts.There are several ways by whichplants produce their offspring. These arecategorised into two types: (i) asexual,and (ii) sexual reproduction. In asexualreproduction plants can give rise to newplants without seeds, whereas in sexualreproduction, new plants are obtainedfrom seeds.Paheli thought that newplants always grow from seeds.But, she has never seen the seedsof sugarcane, potato and rose. Shewants to know how these plantsreproduce.Asexual reproductionIn asexual reproduction new plants areobtained without production of seeds orspores.Vegetative propagationIt is a type of asexual reproduction inwhich new plants are produced fromroots, stems, leaves and buds. Sincereproduction is through the vegetativeparts of the plant, it is known asvegetative propagation.Activity 12.1Cut a branch of rose or champa with anode. This piece of branch is termed acutting. Bury the cutting in the soil. Anode is a part of the stem/branch at

www.GOALias.blogspot.comwhich a leaf arises (Fig. 12.1). Water thecutting every day and observe itsgrowth. Observe and record the numberof days taken for roots to come out andnew leaves to arise. Try the same activityby growing money plant in a jar of waterand record your observations.EyesFig. 12.2 Potato plant sprouting from an ‘eye’Nodeof a potato, each with an eye and burythem in the soil. Water the piecesregularly for a few days and observetheir progress. What do you find?Bud inthe axilFig. 12.1 Stem-cutting of roseYou must have seen flower budsdeveloping into flowers. Apart fromflower buds, there are buds in the axil(point of attachment of the leaf at thenode) of leaves which develop intoshoots. These buds are called vegetativebuds (Fig. 12.2). A bud consists of ashort stem around which immatureoverlapping leaves are folded. Thevegetative buds can also give rise to newplants.Activity 12.2Take a fresh potato. Observe the scarson it with the help of a magnifying glass.You may find bud(s) in them. These scarsare also called “eyes”. Cut a few pieces134Fig. 12.3 Ginger with new plants sproutingfrom itLikewise you can also grow ginger orturmeric (Fig. 12.3).Bryophyllum (sprout leaf plant) hasbuds in the margins of leaves (Fig. 12.4).If a leaf of this plant falls on a moistsoil, each bud can give rise to a newplant.SCIENCE

www.GOALias.blogspot.comNew plantFig. 12.4 Leaf of bryophyllum with buds in themarginThe roots of some plants can alsogive rise to new plants. Sweet potato anddahlia are examples.Plants such as cacti produce newplants when their parts get detachedfrom the main plant body. Eachdetached part can grow into a newplant.Boojho wants to know ifthere is any advantage ofvegetative propagation.multiply every few hours if sufficientnutrients are made available to them.Remember that yeast is a single-celledorganism. Let us see how theyreproduce?Activity 12.3(To be demonstrated by the teacher)Take a piece of yeast cake or yeastpowder from a bakery or a chemist shop.Take a pinch of yeast and place it in acontainer with some water. Add aspoonful of sugar and shake to dissolveit. Keep it in the warm part of a room.After an hour, put a drop of this liquidon a glass slide and observe under amicroscope. What do you observe? Youmay see the formation of new yeast cells(Fig. 12.5).Yeast cellDeveloping budChain of budsNew budPlants produced by vegetativepropagation take less time to grow andbear flowers and fruits earlier than thoseproduced from seeds. The new plantsare exact copies of the parent plant, asthey are produced from a single parent.Later in this chapter you will learnthat plants produced by sexualreproduction have characters of both theparents. Plants produce seeds as a resultof sexual reproduction.BuddingYou have already learnt about the tinyorganisms like yeast can be seen onlyunder a microscope. These grow andFig. 12.5 Reproduction in yeast by buddingThe small bulb-like projectioncoming out from the yeast cell is calleda bud. The bud gradually grows andgets detached from the parent cell andforms a new yeast cell. The new yeastcell grows, matures and produces moreyeast cells. If this process continues, alarge number of yeast cells are producedin a short time.135REPRODUCTIONIN PLANTS135

www.GOALias.blogspot.comFragmentationYou might have seen slimy greenpatches in ponds, or in other stagnantwater bodies. These are the algae. Whenwater and nutrients are available algaegrow and multiply rapidly byfragmentation. An alga breaks up intotwo or more fragments. These fragmentsor pieces grow into new individuals(Fig. 12.6). This process continues andthey cover a large area in a short periodof time.SoriFig. 12.8 Reproduction through spore formationin fernFig. 12.6 Fragmentation in spirogyra (an alga)Spore formationIn Chapter 1 you learnt that the fungion a bread piece grow from spores whichare present in the air. Repeat Activity1.2. Observe the spores in the cotton-HyphaSporangiumSporesFig. 12.7 Reproduction through spore formationin funguslike mesh on the bread. When sporesare released they keep floating in theair. As they are very light they can coverlong distances.The spores are asexual reproductivebodies. Each spore is covered by ahard protective coat to withstandunfavourable conditions such as hightemperature and low humidity. Sothey can survive for a long time. Underfavourable conditions, a sporegerminates and develops into a newindividual. Plants such as moss andferns (Fig. 12.8) also reproduce bymeans of spores.12.2 SEXUALREPRODUCTIONYou have learnt earlier the structure ofa flower. You know that the flowers arethe reproductive parts of a plant. Thestamens are the male reproductive partand the pistil is the female reproductivepart (Fig. 12.9).136SCIENCE

www.GOALias.blogspot.comActivity 12.4Take a mustard/china rose/petuniaflower and separate its reproductiveparts. Study the various parts of astamen and pistil.The flowers which contain eitheronly the pistil or only the stamens arecalled unisexual flowers. The flowerswhich contain both stamens and pistilare called bisexual flowers. Corn,papaya and cucumber produceunisexual flowers, whereas mustard,rose and petunia have bisexual flowers.Both the male and the female unisexualflowers may be present in the same plantor in different plants.Could you identify the anther andthe filament of a stamen? [Fig. 12.9 (a)].Anther contains pollen grains whichproduce male gametes. A pistil consistsof stigma, style and ovary. The ovarycontains one or more ovules. Thefemale gamete or the egg is formed inan ovule [Fig. 12.9 (b)]. In sexualreproduction a male and a femalegamete fuse to form a zygote.AntherBoojho wants to know how themale gamete in the pollen grainreaches the female gamete presentin the ovule.Stigma(a) StamenFilamentStigmaPollinationGenerally pollen grains have a toughprotective coat which prevents themfrom drying up. Since pollen grains arelight, they can be carried by wind orStyleOvulePollensAntherStigmaOvary(b) PistilFig. 12.9 Reproductive parts(a) Self-pollination(b) Cross-pollinationFig. 12.10 Pollination in flower137REPRODUCTIONIN PLANTS137

www.GOALias.blogspot.comBoojho wants to know whyflowers are generally so colourfuland fragrant. Is it to attractinsects?water. Insects visit flowers and carryaway pollen on their bodies. Some ofthe pollen lands on the stigma of a flowerof the same kind. The transfer of pollenfrom the anther to the stigma of a floweris called pollination. If the pollen landson the stigma of the same flower it iscalled self-pollination. When the pollenof a flower lands on the stigma of anotherflower of the same plant, or that of adifferent plant of the same kind, it iscalled cross-pollination [Fig. 12.10 (a)and (b)].Pollen grain (germinating)FertilisationThe cell which results after fusion ofthe gametes is called a zygote. Theprocess of fusion of male and female138(a)Pollen tubeOvum(b)ZygoteformationFig. 12.11 Fertilisation (Zygote formation)(a)(b)Fig. 12.12 (a) Section of an apple, (b) Almondgametes (to form a zygote) is calledfertilisation (Fig. 12.11). The zygotedevelops into an embryo.12.3 FRUITSAND SEEDFORMATIONAfter fertilisation, the ovary grows intoa fruit and other parts of the flower falloff. The fruit is the ripened ovary. Theseeds develop from the ovules. The seedcontains an embryo enclosed in aprotective seed coat.Some fruits are fleshy and juicy suchas mango, apple and orange. Some fruitsare hard like almonds and walnuts[Fig. 12.12 (a) and (b)].12.4 SEEDDISPERSALIn nature same kind of plants grow atdifferent places. This happens becauseseeds are dispersed to different places.Sometimes after a walk through a forestor a field or a park, you may have foundseeds or fruits sticking to your clothes.SCIENCE

www.GOALias.blogspot.comDid you try to observe how these seedswere clinging to your clothes?What do you think will happen if allseeds of a plant were to fall at the sameplace and grow there? There would besevere competition for sunlight, water,minerals and space. As a result the seedswould not grow into healthy plants.Plants benefit by seed dispersal. Itprevents competition between the plantand its own seedlings for sunlight, waterand minerals. It also enables the plantsto invade new habitats for widerdistribution.Seeds and fruits of plants are carriedaway by wind, water and animals.Winged seeds such as those ofdrumstick and maple [Fig. 12.13 (a) and(b)], light seeds of grasses or hairy seedsof aak (Madar) and hairy fruit ofsunflower [Fig. 12.14 (a), (b)], get blownoff with the wind to far away places.Some seeds are dispersed by water. Thesefruits or seeds usually develop floatingability in the form of spongy or fibrousouter coat as in coconut. Some seedsare dispersed by animals, especiallyspiny seeds with hooks which getattached to the bodies of animals andare carried to distant places. Examplesare Xanthium (Fig. 12.15) and Urena.Some seeds are dispersed when thefruits burst with sudden jerks. The seedsare scattered far from the parent plant.This happens in the case of castor andbalsam.SeedWing(a) (b) (a) (b)Fig. 12.13 Seeds of (a) drumstick andFig. 12.14 (a) The hairy fruit of sunflower and(b) maple(b) hairy seed of madar (aak)Fig. 12.15 Xanthium139REPRODUCTIONIN PLANTS139

www.GOALias.blogspot.comKeywordsAsexual reproductionBuddingEmbryoFertilisationFragmentationGametesHyphaOvulePollen grainPollen tubePollinationSeed dispersalSexual reproductionSporeSporangiumVegetative propagationZygoteWhat you have learnt• All organisms multiply or reproduce their own kind.• In plants there are two modes of reproduction, asexual and sexual.• There are several methods of asexual reproduction such asfragmentation, budding, spore formation and vegetative propagation.• Sexual reproduction involves the fusion of male and female gametes.• In vegetative propagation new plants are produced from differentvegetative parts such as leaves, stems and roots.• Flower is the reproductive part of a plant.• A flower may be unisexual with either the male or the female reproductiveparts.• A bisexual flower has both the male and the female reproductive parts.• The male gametes are found inside the pollen grains and female gametesare found in the ovule.• Pollination is the process of transfer of pollen grains from the anther ofone flower to the stigma of the same or another flower.• Pollination is of two types, self-pollination and cross-pollination. Inself-pollination, pollen grains are transferred from the anther to thestigma of the same flower. In cross-pollination, pollen grains aretransferred from the anther of one flower to the stigma of another flowerof the same kind.• Pollination takes place in plants with the help of wind, water and insects.• The fusion of male and female gametes is called fertilisation.• Fertilised egg is called zygote. Zygote develops into an embryo.• Fruit is the mature ovary whereas ovule develops into a seed, whichcontains the developing embryo.• Seed dispersal is aided by wind, water and animals.• Seed dispersal helps the plants to (i) prevent overcrowding, (ii) avoidcompetition for sunlight, water and minerals and (iii) invade new habitats.140SCIENCE

www.GOALias.blogspot.comExercises1. Fill in the blanks:(a) Production of new individuals from the vegetative part of parent iscalled_____________.(b) A flower may have either male or female reproductive parts. Sucha flower is called_____________.(c) The transfer of pollen grains from the anther to the stigma of thesame or of another flower of the same kind is known as_____________.(d) The fusion of male and female gametes is termed as _____________.(e) Seed dispersal takes place by means of _____________,_____________ and _____________.2. Describe the different methods of asexual reproduction. Give examples.3. Explain what you understand by sexual reproduction.4. State the main difference between asexual and sexual reproduction.5. Sketch the reproductive parts of a flower.6. Explain the difference between self-pollination and cross-pollination.7. How does the process of fertilisation take place in flowers?8. Describe the various ways by which seeds are dispersed.9. Match items in Column I with those in Column II:Column IColumn II(a) Bud (i) Maple(b) Eyes (ii) Spirogyra(c) Fragmentation (iii) Yeast(d) Wings (iv) Bread mould(e) Spores (v) Potato(vi) Rose10. Tick () the correct answer:(a) The reproductive part of a plant is the(i) leaf (ii) stem (iii) root (iv) flower(b) The process of fusion of the male and the female gametes is called(i) fertilisation (ii) pollination(iii) reproduction (iv) seed formation141REPRODUCTIONIN PLANTS141

www.GOALias.blogspot.com(c)(d)(e)Mature ovary forms the(i) seed (ii) stamen(iii) pistil (iv) fruitA spore producing plant is(i) rose (ii) bread mould(iii) potato (iv) gingerBryophyllum can reproduce by its(i) stem (ii) leaves(iii) roots (iv) flowerExtended Learning—g—Activities and Projects1. Make your own cactus garden by collecting pieces cut from differentkinds of cacti. Grow the variety in one single flat container or inseparate pots.2. Visit a fruit market and collect as many local fruits as possible. If manyfruits are not available, you can collect tomatoes and cucumbers (theseare fruits, though we use them as vegetables). Make drawings of thedifferent fruits. Split the fruits and examine the seeds within. Look forany special characteristics in the fruits and their seeds. If possible visitthe website:www.saps.plantsci.cam.ac.uk/fscfruit/dispersal.pdfYou can visit a library also to learn about this.3. Think of ten different fruit-bearing plants. Remember that manyvegetables are also fruits of the plants. Discuss with your teacher,parents, farmers, fruit growers and agricultural experts (if availablenearby) and find out the manner of their dispersal. Present your datain the form of a table as shown below:S. No. Name of fruit-bearing plantAgent through whichseeds are dispersedPart of or seed whichhelps in dispersal1.2.3.4. Suppose there is one member of a particular kind of organism in aculture dish, which doubles itself in one hour through asexualreproduction. Work out the number of members of that kind of organismwhich will be present in the culture dish after ten hours. Such a colonyof individuals arising from one parent is called a “clone”.You can read more on the following website:www.edumedia-sciences.com/a437_l2-blog-call.html142SCIENCE

www.GOALias.blogspot.com1313 Motion and TimeIn Class VI, you learnt about differenttypes of motions. You learnt that amotion could be along a straight line,it could be circular or periodic. Can yourecall these three types of motions?Table 13.1 gives some commonexamples of motions. Identify the typeof motion in each case.Table 13.1 Some examples ofdifferent types of motionExample ofmotionSoldiers in amarch pastBullock cartmoving on astraight roadHands of anathlete in a racePedal of a bicyclein motionMotion of the eartharound the sunMotion of a swingMotion of apendulumType of motionAlong a straightline/circular/periodicIt is common experience that themotion of some objects is slow while thatof some others is fast.13.1 S13.1 SLOWOR FASTWe know that some vehicles move fasterthan others. Even the same vehicle maymove faster or slower at different times.Make a list of ten objects moving alonga straight path. Group the motion ofthese objects as slow and fast. How didyou decide which object is moving slowand which one is moving fast.If vehicles are moving on a road inthe same direction, we can easily tellwhich one of them is moving faster thanthe other.Activity 13.1Look at Fig. 13.1. It shows the positionof some vehicles moving on a road inthe same direction at some instant oftime. Now look at Fig. 13.2. It shows theposition of the same vehicles after sometime. From your observation of the twofigures, answer the following questions:Which vehicle is moving the fastestof all? Which one of them is moving theslowest of all?The distance moved by objects in agiven interval of time can help us todecide which one is faster or slower. Forexample, imagine that you have gone tosee off your friend at the bus stand.Suppose you start pedalling your bicycleat the same time as the bus begins tomove. The distance covered by you after

www.GOALias.blogspot.com5 minutes would be much smaller thanthat covered by the bus. Would you saythat the bus is moving faster than thebicycle?We often say that the faster vehiclehas a higher speed. In a 100-metre race144Fig. 13.1 Vehicles moving in the samedirection on a roadFig. 13.2 Position of vehicles shown inFig. 13.1 after some timeit is easy to decide whose speedis the highest. One who takesshortest time to cover thedistance of 100 metres has thehighest speed.13.2 SPEEDYou are probably familiar withthe word speed. In theexamples given above, a higherspeed seems to indicate that agiven distance has beencovered in a shorter time, or alarger distance covered in agiven time.The most convenient way tofind out which of the two ormore objects is moving fasteris to compare the distancesmoved by them in a unit time.Thus, if we know the distancecovered by two buses in onehour, we can tell which one isslower. We call the distancecovered by an object in a unittime as the speed of the object.When we say that a car ismoving with a speed of 50kilometres per hour, it impliesthat it will cover a distance of50 kilometres in one hour. However, acar seldom moves with a constant speedfor one hour. In fact, it starts movingslowly and then picks up speed. So,when we say that the car has a speed of50 kilometres per hour, we usuallyconsider only the total distance coveredby it in one hour. We do not botherwhether the car has been moving withSCIENCE

www.GOALias.blogspot.coma constant speed or not during thathour. The speed calculated here isactually the average speed of the car. Inthis book we shall use the term speedfor average speed. So, for us the speedis the total distance covered dividedby the total time taken. Thus,Speed =In everyday life we seldom find objectsmoving with a constant speed over longdistances or for long durations of time.If the speed of an object moving alonga straight line keeps changing, itsmotion is said to be non-uniform. Onthe other hand, an object moving alonga straight line with a constant speedis said to be in uniform motion. Inthis case, the average speed is thesame as the actual speed.We can determine the speed of a givenobject once we can measure the timetaken by it to cover a certain distance.In Class VI you learnt how to measuredistances. But, how do we measuretime? Let us find out.13.3 MTotal distance coveredTotal time taken13.3 MEASUREMENTOF TIMEIf you did not have a clock, how wouldyou decide what time of the day it is?Have you ever wondered how our elderscould tell the approximate time of theday by just looking at shadows?How do we measure time interval ofa month? A year?Our ancestors noticed that manyevents in nature repeat themselves afterdefinite intervals of time. For example,they found that the sun rises everydayin the morning. The time between onesunrise and the next was called a day.Similarly, a month was measured fromone new moon to the next. A year wasfixed as the time taken by the earth tocomplete one revolution of the sun.Often we need to measure intervalsof time which are much shorter than aday. Clocks or watches are perhaps themost common time measuring devices.Have you ever wondered how clocks andwatches measure time?The working of clocks is rathercomplex. But all of them make use ofsome periodic motion. One of the mostwell-known periodic motions is that ofa simple pendulum.(a) Wall clock(c) Digital clock(b) Table clockFig. 13.3 Some common clocks145MOTIONAND TIME145

www.GOALias.blogspot.comAFig. 13.4 (a) A simplependulumFig. 13.4 (b) Differentpositions of the bob of anoscillating simple pendulumA simple pendulum consists of asmall metallic ball or a piece of stonesuspended from a rigid stand by athread [Fig. 13.4 (a)]. The metallic ballis called the bob of the pendulum.Fig. 13.4 (a) shows the pendulum atrest in its mean position. When the bobof the pendulum is released after takingit slightly to one side, it begins to moveto and fro [Fig. 13.4 (b)]. The to and fromotion of a simple pendulum is anexample of a periodic or an oscillatorymotion.The pendulum is said to havecompleted one oscillation when its bob,starting from its mean position O, movesOBto A, to B and back to O. Thependulum also completes oneoscillation when its bob movesfrom one extreme position A to theother extreme position B andcomes back to A. The time takenby the pendulum to complete oneoscillation is called its timeperiod.Activity 13.2Set up a simple pendulum asshown in Fig. 13.4 (a) with athread or string of length nearlyone metre. Switch off any fansnearby. Let the bob of thependulum come to rest at itsmean position. Mark the meanposition of the bob on the floorbelow it or on the wall behind it.To measure the time period ofthe pendulum we will needa stopwatch. However, if astopwatch is not available, a tableclock or a wristwatch can be used.To set the pendulum in motion,gently hold the bob and move it slightlyto one side. Make sure that the stringattached to the bob is taut while youdisplace it. Now release the bob from itsdisplaced position. Remember that thebob is not to be pushed when it isreleased. Note the time on the clockwhen the bob is at its mean position.Instead of the mean position you maynote the time when the bob is at one ofits extreme positions. Measure the timethe pendulum takes to complete 20oscillations. Record your observations146SCIENCE

www.GOALias.blogspot.comin Table 13.2. The first observationshown is just a sample. Yourobservations could be different fromthis. Repeat this activity a few times andrecord your observations. By dividingthe time taken for 20 oscillations by 20,get the time taken for one oscillation, orthe time period of the pendulum.Is the time period of your pendulumnearly the same in all cases?Note that a slight change in the initialdisplacement does not affect the timeperiod of your pendulum.Nowadays most clocks or watcheshave an electric circuit with one or moreTable 13.2 Time period of a simplependulumLength of the string = 100 cmS.No. Time taken for 20oscillations1. 42 s 2.1 s2.3.Time periodcells. These clocks are called quartzclocks. The time measured by quartzclocks is much more accurate than thatby the clocks available earlier.Units of time and speedThe basic unit of time is a second. Itssymbol is s. Larger units of time areminutes (min) and hours (h). Youalready know how these units are relatedto one another.What would be the basic unit ofspeed?Since the speed is distance/time, thebasic unit of speed is m/s. Of course, itcould also be expressed in other unitssuch as m/min or km/h.You must remember that thesymbols of all units are written insingular. For example, we write 50 kmand not 50 kms, or 8 cm and not 8 cms.Boojho is wondering how manyseconds there are in a day and howmany hours in a year. Can you helphim?There is an interesting story about the discovery that the time period of a givenpendulum is constant. You might have heard the name of famous scientistGalileo Galilie (A.D. 1564 –1642). It is said that once Galileo was sitting in achurch. He noticed that a lamp suspended from the ceiling with a chain wasmoving slowly from one side to the other. He was surprised to find that hispulse beat the same number of times during the interval in which the lampcompleted one oscillation. Galileo experimented with various pendulums toverify his observation. He found that a pendulum of a given length takes alwaysthe same time to complete one oscillation. This observation led to thedevelopment of pendulum clocks. Winding clocks and wristwatches wererefinements of the pendulum clocks.147MOTIONAND TIME147

www.GOALias.blogspot.comDifferent units of time are useddepending on the need. For example, itis convenient to express your age inyears rather than in days or hours.Similarly, it will not be wise to expressin years the time taken by you to coverthe distance between your home andyour school.How small or large is a time intervalof one second? The time taken in sayingaloud “two thousand and one” is nearbyone second. Verify it by counting aloudfrom "two thousand and one" to "twothousand and ten". The pulse of anormal healthy adult at rest beats about72 times in a minute that is about 12times in 10 seconds. This rate may beslightly higher for children.Paheli wondered how time wasmeasured when pendulumclocks were not available.Many time measuring devices wereused in different parts of the world beforethe pendulum clocks became popular.Sundials, water clocks and sand clocksare some examples of such devices.Different designs of these devices weredeveloped in different parts of the world(Fig. 13.5).13.4 MEASURINGSPEEDHaving learnt how to measure time anddistance, you can calculate the speed ofan object. Let us find the speed of a ballmoving along the ground.Activity 13.3Draw a straight line on the ground withchalk powder or lime and ask one ofyour friends to stand 1 to 2 m away fromit. Let your friend gently roll a ball alongthe ground in a direction perpendicularto the line. Note the time at the momentthe ball crosses the line and also whenit comes to rest (Fig. 13.6). How muchtime does the ball take to come to rest?The smallest time interval that can be measured with commonly availableclocks and watches is one second. However, now special clocks are availablethat can measure time intervals smaller than a second. Some of these clockscan measure time intervals as small as one millionth or even one billionth of asecond. You might have heard the terms like microsecond and nanosecond.One microsecond is one millionth of a second. A nanosecond is one billionthof a second. Clocks that measure such small time intervals are used for scientificresearch. The time measuring devices used in sports can measure time intervalsthat are one tenth or one hundredth of a second. On the other hand, times ofhistorical events are stated in terms of centuries or millenniums. The ages ofstars and planet are often expressed in billions of years. Can you imagine therange of time intervals that we have to deal with?148SCIENCE

www.GOALias.blogspot.com(b) Sand clock(a) Sundial at Jantar Mantar, Delhi(c) Water clockFig. 13.5 Some ancient time-measuring devicesFig. 13.6 Measuring the speed of a ballMeasure the distance between the pointat which the ball crosses the line andthe point where it comes to rest. Youcan use a scale or a measuringtape. Let different groups repeat theactivity. Record the measurements inTable 13.3. In each case calculate thespeed of the ball.You may now like to compare yourspeed of walking or cycling with that ofyour friends. You need to know thedistance of the school from your homeor from some other point. Each one ofyou can then measure the time takento cover that distance and calculate yourspeed. It may be interesting to know whoamongst you is the fastest. Speeds ofsome living organisms are given in149MOTIONAND TIME149

www.GOALias.blogspot.comTable 13.3 Distance moved and time taken by a moving ballName of the groupDistance moved byTime taken (s)Speed = Distance/the ball (m)Time taken (m/s)Table 13.4, in km/h. You can calculatethe speeds in m/s yourself.Rockets, launching satellites intoearth’s orbit, often attain speeds up to8 km/s. On the other hand, a tortoisecan move only with a speed of about 8cm/s. Can you calculate how fast is therocket compared with the tortoise?Once you know the speed of anobject, you can find the distance movedby it in a given time. All you have to dois to multiply the speed by time. Thus,Distance covered = Speed TimeYou can also find the time an objectwould take to cover a distance whilemoving with a given speed.Time taken = Distance/SpeedBoojho wants to knowwhether there is any devicethat measures the speed.You might have seen a meter fittedon top of a scooter or a motorcycle.Similarly, meters can be seen on thedashboards of cars, buses and othervehicles. Fig. 13.7 shows the dashboardof a car. Note that one of the meters haskm/h written at one corner. This iscalled a speedometer. It records theTable 13.4 Fastest speed that some animals can attainS. No. Name of the objectSpeed in km/hSpeed in m/s1. Falcon 3202. Cheetah 1123. Blue fish 40 – 464. Rabbit 565. Squirrel 196. Domestic mouse 117. Human 408. Giant tortoise 0.279. Snail 0.05320 10 0 060 60150SCIENCE

www.GOALias.blogspot.com13.5 D13.5 DISTANCEISTANCE-TIMEIME GRAPHYou might have seen that newspapers,magazines, etc., present information invarious forms of graphs to make itTable 13.5 Odometer reading atdifferent times of the journeyTime(AM)OdometerreadingDistance fromthe startingpoint8:00 AM 36540 km 0 km8:30 AM 36560 km 20 km9:00 AM 36580 km 40 km9:30 AM 36600 km 60 kmFig. 13.7 The dashboard of a carspeed directly in km/h. There is alsoanother meter that measures thedistance moved by the vehicle. Thismeter is known as an odometer.While going for a school picnic, Pahelidecided to note the reading on theodometer of the bus after every30 minutes till the end of the journey.Later on she recorded her readings inTable 13.5.Can you tell how far was the picnicspot from the school? Can you calculatethe speed of the bus? Looking at theTable, Boojho teased Paheli whether shecan tell how far they would havetravelled till 9:45 AM. Paheli had noanswer to this question. They went totheir teacher. She told them that oneway to solve this problem is to plot adistance-time graph. Let us find out howsuch a graph is plotted.10:00 AM 36620 km 80 kmFig. 13.8 A bar graph showing runs scored bya team in each overinteresting. The type of graph shown inFig. 13.8 is known as a bar graph.Another type of graphical representationis a pie chart (Fig. 13.9). The graphshown in Fig. 13.10 is an example of aline graph. The distance-time graph is aline graph. Let us learn to make such agraph.151MOTIONAND TIME151

www.GOALias.blogspot.comOxygenOther gasesYX O XWeight (in kg)Fig. 13.9 A pie chart showing compositionof airY80706050403020102 4 6 8 10 12 14 16 18 20 22Age (in year)NitrogenFig. 13.10 A line graph showing change inweight of a man with ageTake a sheet of graph paper. Drawtwo lines perpendicular to each otheron it, as shown in Fig. 13.11. Mark thehorizontal line as XOX'. It is known asthe x-axis. Similarly mark the verticalline YOY'. It is called the y-axis. The pointof intersection of XOX' and YOY' isknown as the origin O. The twoquantities between which the graph isdrawn are shown along these two axes.We show the positive values on thex-axis along OX. Similarly, positivevalues on the y-axis are shown alongOY. In this chapter we shall consideronly the positive values of quantities.XYFig. 13.11 x-axis and y-axis on a graph paperTherefore, we shall use only the shadedpart of the graph shown in Fig. 13.11.Boojho and Paheli found out thedistance travelled by a car and the timetaken by it to cover that distance. Theirdata is shown in Table 13.6.Table 13.6 The motion of a carS. No. Time1. 0 0Distance2. 1 min 1 km3. 2 min 2 km4. 3 min 3 km5. 4 min 4 km6. 5 min 5 kmYou can make the graph by followingthe steps given below:• Draw two perpendicular lines torepresent the two axes and markthem as OX and OY as in Fig. 13.11.• Decide the quantity to be shownalong the x-axis and that to beshown along the y-axis. In this case152SCIENCE

www.GOALias.blogspot.comwe show the time along the x-axisand the distance along the y-axis.• Choose a scale to represent thedistance and another to representthe time on the graph. For the motionof the car scales could beTime: 1 min = 1 cmDistance: 1 km = 1 cm• Mark values for the time and thedistance on the respective axesaccording to the scale you havechosen. For the motion of the carmark the time 1 min, 2 min, … onthe x-axis from the origin O.Similarly, mark the distance 1 km,2 km … on the y-axis (Fig. 13.12).• Now you have to mark the points onthe graph paper to represent eachset of values for distance and time.Observation recorded at S. No. 1in Table 13.6 shows that at time0 min the distance moved is alsozero. The point corresponding to thisset of values on the graph willtherefore be the origin itself. After 1minute, the car has moved a distanceof 1 km. To mark this set of valueslook for the point that represents1 minute on the x-axis. Draw a lineparallel to the y-axis at this point.Then draw a line parallel to thex-axis from the point correspondingto distance 1 km on the y-axis. Thepoint where these two linesintersect represents this set of valueson the graph (Fig. 13.12). Similarly,mark on the graph paper thepoints corresponding to differentsets of values.OOYYFig. 13.12 Making a graphFig. 13.13 Making a graph• Fig. 13.13 shows the set of points onthe graph corresponding to positionsof the car at various times.• Join all the points on the graph asshown in Fig. 13.13. It is a straightline. This is the distance-time graphfor the motion of the car.• If the distance-time graph is astraight line, it indicates that theobject is moving with a constantspeed. However, if the speed of theobject keeps changing, the graph canbe of any shape.XX153MOTIONAND TIME153

www.GOALias.blogspot.comYXFig. 13.14 Distance-time graph of the busGenerally, the choice of scales is notas simple as in the example given above.We may have to choose two different scalesto represent the desired quantities on thex-axis and the y-axis. Let us try tounderstand this process with an example.Let us again consider the motion ofthe bus that took Paheli and her friendsto the picnic. The distance covered andtime taken by the bus are shown inTable 13.5. The total distance coveredby the bus is 80 km. If we decide tochoose a scale 1 km = 1 cm, we shallhave to draw an axis of length 80 cm.This is not possible on a sheet of paper.On the other hand, a scale 10 km = 1cm would require an axis of length only8 cm. This scale is quite convenient.However, the graph may cover only asmall part of the graph paper. Some ofthe points to be kept in mind whilechoosing the most suitable scale fordrawing a graph are:• the difference between the highestand the lowest values of eachquantity.• the intermediate values of eachquantity, so that with the scalechosen it is convenient to mark thevalues on the graph, and• to utilise the maximum part of thepaper on which the graph is to bedrawn.Suppose that we have a graph paperof size 25 cm 25 cm. One of the scaleswhich meets the above conditions andcan accommodate the data of Table 13.5could beDistance: 5 km = 1 cm, andTime: 6 min = 1 cmCan you now draw the distance-timegraph for the motion of the bus? Is thegraph drawn by you similar to thatshown in Fig. 13.13?Distance-time graphs provide avariety of information about the motion154SCIENCE

www.GOALias.blogspot.comwhen compared to the data presentedby a table. For example, Table 13.5 givesinformation about the distance movedby the bus only at some definite timeintervals. On the other hand, from thedistance-time graph we can find thedistance moved by the bus at anyinstant of time. Suppose we want toknow how much distance the bus hadtravelled at 8:15 AM. We mark the pointcorresponding to the time (8:15 AM) onthe x-axis. Suppose this point is A. Nextwe draw a line perpendicular to thex-axis (or parallel to the y-axis) atpoint A. We then mark the point, T, onthe graph at which this perpendicularline intersects it (Fig. 13.14). Next, wedraw a line through the point T parallelto the x-axis. This intersects the y-axisat the point B. The distancecorresponding to the point B on they-axis, OB, gives us the distance in kmcovered by the bus at 8:15 AM. How mucis this distance in km? Can you nowhelp Paheli to find the distance movedby the bus at 9:45 AM? Can you alsofind the speed of the bus from itsdistance-time graph?KeywordsBar graphGraphsNon-uniform motionOscillationSimple pendulumSpeedTime periodUniform motionUnit of timeWhat you have Learnt• The distance moved by an object in a unit time is called its speed.• Speed of objects help us to decide which one is moving faster than theother.• The speed of an object is the distance travelled divided by the time takento cover that distance. Its basic unit is metre per second (m/s).• Periodic events are used for the measurement of time. Periodic motion ofa pendulum has been used to make clocks and watches.• Motion of objects can be presented in pictorial form by theirdistance-time graphs.• The distance-time graph for the motion of an object moving with a constantspeed is a straight line.155MOTIONAND TIME155

www.GOALias.blogspot.comExercises1. Classify the following as motion along a straight line, circular oroscillatory motion:(i)(ii)(iii)(iv)(v)(vi)Motion of your hands while running.Motion of a horse pulling a cart on a straight road.Motion of a child in a merry-go-round.Motion of a child on a see-saw.Motion of the hammer of an electric bell.Motion of a train on a straight bridge.2. Which of the following are not correct?(i)(ii)(iii)(iv)(v)The basic unit of time is second.Every object moves with a constant speed.Distances between two cities are measured in kilometres.The time period of a given pendulum is not constant.The speed of a train is expressed in m/h.3. A simple pendulum takes 32 s to complete 20 oscillations. What is thetime period of the pendulum?4. The distance between two stations is 240 km. A train takes 4 hours tocover this distance. Calculate the speed of the train.5. The odometer of a car reads 57321.0 km when the clock shows the time08:30 AM. What is the distance moved by the car, if at 08:50 AM, theodometer reading has changed to 57336.0 km? Calculate the speed ofthe car in km/min during this time. Express the speed in km/h also.6. Salma takes 15 minutes from her house to reach her school on abicycle. If the bicycle has a speed of 2 m/s, calculate the distancebetween her house and the school.7. Show the shape of the distance-time graph for the motion in thefollowing cases:(i)(ii)A car moving with a constant speed.A car parked on a side road.8. Which of the following relations is correct?(i) Speed = Distance Time (ii) Speed = DistanceTime(iii) Speed =TimeDistance(iv) Speed =1DistanceTime156SCIENCE

www.GOALias.blogspot.com9. The basic unit of speed is:(i) km/min (ii) m/min(iii) km/h (iv) m/s10. A car moves with a speed of 40 km/h for 15 minutes and then with aspeed of 60 km/h for the next 15 minutes. The total distance covered bythe car is:(i) 100 km (ii) 25 km(iii) 15 km (iv) 10 km11. Suppose the two photographs, shown in Fig. 13.1 and Fig. 13.2, hadbeen taken at an interval of 10 seconds. If a distance of 100 metres isshown by 1 cm in these photographs, calculate the speed of the blue car.12. Fig. 13.15 shows the distance-time graph for the motion of two vehicles Aand B. Which one of them is moving faster?Fig. 13.15 Distance-time graph for the motion of two cars13. Which of the following distance-time graphs shows a truck moving withspeed which is not constant?(i)(ii)157MOTIONAND TIME157

www.GOALias.blogspot.comExtend Learning (iii)— Activities and (iv)Projects1. You can make your own sundial and use it to mark the time of the day atyour place. First of all find the latitude of your city with the help of anatlas. Cut out a triangular piece of a cardboard such that its one angleis equal to the latitude of your place and the angle opposite to it is aright angle. Fix this piece, called gnomon, vertically along a diameter ofa circular board a shown in Fig. 13.16. One way to fix the gnomon couldbe to make a groove along a diameter on the circular board.Next, select an open space, which receives sunlight for most of the day.Mark a line on the ground along the North-South direction. Place thesundial in the sun as shown in Fig. 13.16. Mark the position of the tipof the shadow of the gnomon on the circular board as early in the dayas possible, say 8:00 AM. Mark the position of the tip of the shadowevery hour throughout the day. Draw lines to connect each point markedby you with the centre of the base of the gnomon as shown in Fig. 13.16.Extend the lines on the circular board up to its periphery. You can usethis sundial to read the time of the day at your place. Remember thatthe gnomon should always be placed in the North-South direction asshown in Fig. 13.16.2. Collect information about time-measuring devices that were used in theFig. 13.16158SCIENCE

www.GOALias.blogspot.comancient times in different parts of the world. Prepare a brief write up oneach one of them. The write up may include the name of the device, theplace of its origin, the period when it was used, the unit in which the timewas measured by it and a drawing or a photograph of the device, ifavailable.3. Make a model of a sand clock which can measure a time interval of 2minutes (Fig. 13.17).Fig. 13.174. You can perform an interesting activity when you visit a park to ride aswing. You will require a watch. Make the swing oscillate withoutanyone sitting on it. Find its time period in the same way as you did forthe pendulum. Make sure that there are no jerks in the motion of theswing. Ask one of your friends to sit on the swing. Pushit once and let it swing naturally. Again measure its time period.Repeat the activity with different persons sitting on the swing. Comparethe time period of the swing measured in different cases. Whatconclusions do you draw from this activity?Did you know?The time-keeping services in India are provided by the National PhysicalLaboratory, New Delhi. The clock they use can measure time intervalswith an accuracy of one-millionth of a second. The most accurate clockin the world has been developed by the National Institute of Standardsand Technology in the U.S.A. This clock will lose or gain one second afterrunning for 20 million years.159MOTIONAND TIME159

www.GOALias.blogspot.com1414 Electric Current and itsEffectsYou might have tried the game‘How steady is your hand?’suggested in Chapter 12 ofClass VI. If not, you may try it out now.Paheli and Boojho had also set up thegame by connecting an electric circuitas suggested in Class VI. They had lotsof fun trying it out with their familiesand friends. They enjoyed it so muchthat they decided to suggest it to acousin of theirs who stayed in adifferent town. So, Paheli made a neatdrawing showing how the variouselectric components were to beconnected (Fig.14.1).Fig. 14.1 Setup to check how steadyyour hand isCan you draw this circuitconveniently? It made Boojho wonder ifthere was an easier way to representthese electric components.14.1 S14.1 SYMBOLSOF ELECTRICCOMPONENTSSome common electric components canbe represented by symbols. In Table 14.1,some electric components and theirsymbols are shown. You may comeacross different symbols for thesecomponents in different books. However,in this book, we shall be using thesymbols shown here.Look at the symbols carefully. In thesymbol for the electric cell, notice thatthere is a longer line and a shorter butthicker parallel line. Do you recall thatan electric cell has a positive terminaland a negative terminal? In the symbolof the electric cell, the longer linerepresents the positive terminal and thethicker, shorter line represents thenegative terminal.For a switch the ‘ON’ position andthe ‘OFF’ position are represented by thesymbols as shown. The wires used toconnect the various components in acircuit are represented by lines.In Table 14.1, a battery and itssymbol are also shown. Do you knowwhat a battery is? Look at the symbol ofa battery. Can you make out what abattery could be? For some of theactivities we may need more than onecell. So, we connect two or more cellstogether as shown in Fig.14.2. Notice160SCIENCE

www.GOALias.blogspot.comTable 14.1 Symbols for someelectric circuit componentsS.No. Electric componentSymbol1. Electric cell2. Electric bulb3. Switch in ‘ON’ position4. Switch in ‘OFF’ positionMany devices such as torches,transistors, toys, TV remote controls, usebatteries. However, in some of thesedevices the electric cells are not alwaysplaced one after the other as shown inFig. 14.2. Sometimes the cells are placedside by side. Then how are the terminalsof the cells connected? Look carefullyinside the battery compartment of anydevice. There is usually a thick wire ora metal strip connecting the positiveterminal of one cell to the negativeterminal of the next cell (Fig.14.3). Inorder to help you to place the cellscorrectly in the battery compartment,‘+’ and ‘–’ symbols are usually printedthere.How can we connect the cells toprepare batteries for our activities? Youmay make a cell holder, as shown inFig.14.4, using a wooden block, two ironstrips and rubber bands. It is necessary5. Battery(a)(b)6. WireFig. 14.2 (a) A battery of two cells(b) A battery of four cellsthat the positive terminal of one cell isconnected to the negative terminal of thenext cell. Such a combination of two ormore cells is called a battery.Fig. 14.3 Connecting two cells together to makea battery161ELECTRICCURRENTAND ITS EFFECTS161

www.GOALias.blogspot.comthat the rubber bands hold the metalstrips tightly.You could also buy cell holders fromthe market for making batteries of twoor more electric cells. Place the cells inthem properly, such that the positive162Fig. 14.4 A cell holderFig. 14.5 Holder for battery of two cellsPaheli and Boojho wonder whetherthe batteries used in tractors, trucksand inverters are also made from cells.Then why is it called a battery? Canyou help them to find the answer tothis question?Fig. 14.6 Truck battery and its cutoutterminal of one cell is connected to thenegative terminal of the next cell.Connect a piece of wire each to the twometal clips on the cell holder as shownin Fig.14.5. Your battery is ready for use.The symbol used for representing abattery is shown in Table.14.1. It hasthree cells. Therefore, it has three pairsof long and short parallel lines.Let us now draw a circuit diagram ofan electric circuit using symbols shownin Table 14.1.Activity 14.1Make the electric circuit shown inFig. 14.7. You used a similar circuit inClass VI to make an electric bulb glow.Do you remember that the bulb glowsonly when the switch is in the ‘ON’position? The bulb glows as soon as theswitch is moved to the ‘ON’ position.Copy this electric circuit in yournotebook. Make also a circuit diagramof this circuit using symbols for thevarious electric components.Is your diagram similar to the oneshown in Fig. 14.8?It is much easier to draw a circuitdiagram using symbols. Therefore, wegenerally represent an electric circuit byits circuit diagram.Fig. 14.9 shows another circuitdiagram. Is it identical to the circuitdiagram shown in Fig.14.8? In whichway is it different?Would the bulb glow in this electriccircuit? Recall that the bulb glows onlywhen the switch is in the ‘ON’ positionand the electric circuit is closed.SCIENCE

www.GOALias.blogspot.comFig. 14.7 An electric circuitFig. 14.8 Circuit diagram of electric circuitshown in Fig. 14.7• Notice that the key or switch canbe placed anywhere in the circuit.• When the switch is in the ‘ON’position, the circuit from thepositive terminal of the battery tothe negative terminal is complete.The circuit is then said to be closedand the current flows throughoutthe circuit instantly.• When the switch is in the ‘OFF’position, the circuit is incomplete.It is said to be open. No currentflows through any part of thecircuit.In the bulb there is a thin wire, calledthe filament, which glows when anFig. 14.9 Another circuit diagramelectric current passes through it. Whenthe bulb gets fused, its filament isbroken.If the filament of the bulb is broken,would the circuit be complete? Wouldthe bulb still glow?You might have noticed that aglowing electric bulb become warm. Doyou know why?14.2 HEATINGEFFECTOF ELECTRICCURRENTActivity 14.2CAUTIONNever touch a lighted electric bulbconnected to the mains. It may be veryhot and your hand may get burntbadly. Do not experiment with theelectric supply from the mains or agenerator or an inverter. You may getan electric shock, which may bedangerous. Use only electric cells forall the activities suggested here.Take an electric cell, a bulb, a switchand connecting wires. Make an electriccircuit as shown in Fig.14.9. Thisactivity has to be done using only onecell. Keep the switch in the ‘OFF’163ELECTRICCURRENTAND ITS EFFECTS163

www.GOALias.blogspot.composition. Does the bulb glow? Touchthe bulb. Now move the electric switchto the ‘ON’ position and let the bulb glowfor a minute or so. Again touch the bulb.Do you feel any difference? After movingthe switch back to the ‘OFF’ position,touch the bulb again.Activity 14.3Make a circuit as shown in Fig.14.10.Take about 10 cm long piece of nichromewire and tie it between the nails. (Youcan get nichrome wire from an electricrepair shop or you can use a piece ofdiscarded coil of an electric heater.)Touch the wire. Now switch on thecurrent in the circuit by moving theswitch to the ‘ON’ position. After a fewFig. 14.10CAUTIONDo not keep the switch in the ‘ON’position for a long time, otherwise thecell may become weak very quickly.seconds touch the wire. (Do not hold itfor a long time.) Switch off the current.Touch the wire again after a fewminutes.The wire gets hot when an electriccurrent passes through it. This is theheating effect of the electric current.Can you think of any electric appliancewhere the heating effect of the electriccurrent is used? Make a list of suchappliances.You might have seen an electricroom heater or an electric heater usedfor cooking. All these contain a coil ofwire. This coil of wire is called anelement. You may have noticed thatwhen these appliances are switched onBoojho could not see element in anelectric iron. Paheli told him thatelectrical appliances, such asimmersion heaters, hotplates, irons,geysers, electric kettles, hair dryers,have elements inside them. Have youever seen the element in anyappliance?Fig. 14.11 Element of electric iron164SCIENCE

www.GOALias.blogspot.comFig. 14.12 Glowing filament of an electric bulbafter connecting to the electric supply,their elements become red hot and giveout heat.The amount of heat produced in awire depends on its material, lengthand thickness. Thus, for differentrequirements, the wires of differentmaterials and different lengths andthicknesses are used.The wires used for making electriccircuits do not normally become hot. Onthe other hand, the elements of someelectric appliances become so hot thatthey are easily visible. The filament ofan electric bulb gets heated to such ahigh temperature that it starts glowing.If a large current passes through awire the wire may become so hot that itmay even melt and break. But is itpossible for a wire to melt and break?Let us check it out.Activity 14.4Make the circuit we used for Activity 14.3again. However, replace the cell with abattery of four cells. Also, in place ofAn electric bulb is used for light but it also gives heat. This is not desirable. Thisresults in the wastage of electricity. This wastage can be reduced by usingfluorescent tube lights in place of the bulbs. Compact fluorescent lamps (CFLs)also reduce wastage and can be fixed in the ordinary bulb holders.Fig. 14.13 Tube lights and CFLsHowever, before buying bulbs or tubes, or CFLs, look for the ISI mark of theBureau of Indian Standards. In fact, before buying any electrical appliance,look for this mark. The ISI mark ensures that the appliance is safe and wastageof energy is minimum.165ELECTRICCURRENTAND ITS EFFECTS165

www.GOALias.blogspot.comFig. 14.15 Fuses used in electrical appliancesFig. 14.14 Fuse used in buildingsthe nichrome wire, tie a thin strand ofsteel wool. (The steel wool is commonlyused for cleaning utensils and isavailable in grocery shops.) If there areany fans in the room, switch them off.Now pass the current through the circuitfor sometime. Observe the strand of steelwool carefully. Note what happens. Doesthe strand of steel wool melt and break?Wires made from some specialmaterials melt quickly and break whenlarge electric currents are passedthrough them. These wires are used formaking electric fuses (Fig.14.14). In allbuildings fuses are inserted in allelectrical circuits. There is a maximumlimit on the current which can safelyflow through a circuit. If by accident thecurrent exceeds this safe limit, the wiresmay become overheated and may causefire. If a proper fuse is there in the circuit,it will blow off and break the circuit. Afuse is thus a safety device whichprevents damages to electrical circuitsand possible fires.Fuses of different kinds are usedfor different purposes. Fig. 14.14 showsfuses used in our houses. Fusesshown in Fig. 14.15 are generally usedin electrical appliances.CAUTIONNever try to investigate an electric fuseconnected to mains circuit on yourown. You may, however, visit anelectric repair shop and compare theburnt out fuses with the new ones.One reason for excessive currents inelectrical circuits is the directtouching of wires. This may happen ifthe insulation on the wires has comeoff due to wear and tear. This maycause a short circuit. Another reasonfor excessive current can be theconnection of many devices to a singlesocket. This may cause overload inthe circuit. You might have readreports in newspapers about firescaused by short circuits andoverloads.We observed the heating effect of theelectric current and learnt how we useit to our advantage. Does the electriccurrent have other effects also?166SCIENCE

www.GOALias.blogspot.comThese days Miniaturecircuit breakers (MCBs)are increasingly beingused in place of fuses.These are switches whichautomatically turn offwhen current in a circuitexceeds the safe limit. Youturn them on and thecircuit is once againcomplete. Look for ISImark on MCBs also.Fig. 14.16 Miniaturecircuit breaker (MCB)Fig. 14.17 Effect of current on acompass needle14.3 M14.3 MAGNETICEFFECTOFELECTRICCURRENTActivity 14.5CAUTIONAlways, use proper fuses which havebeen specified for particularapplications, carrying ISI mark. Neveruse just any wire or strip of metal inplace of a fuse.Take the cardboard tray from inside adiscarded matchbox. Wrap an electricwire a few times around the cardboardtray. Place a small compass needleinside it. Now connect the free ends ofthis wire to an electric cell through aswitch as shown in Fig.14.17.Note the direction in which thecompass needle is pointing. Bring a barmagnet near the compass needle.Observe what happens. Now, whilewatching the compass needle carefully,move the switch to the ‘ON’ position.What do you observe? Does the compassneedle deflect? Move the switch back tothe ‘OFF’ position. Does the compassneedle come back to its initial position?Repeat the experiment a few times.What does this experiment indicate?We know that the needle of a compassis a tiny magnet, which points innorth-south direction. When we bringa magnet close to it, the needle getsdeflected. We have also seen thatFig. 14.18 Hans Christian Oersted(A.D. 1777-1851)167ELECTRICCURRENTAND ITS EFFECTS167

www.GOALias.blogspot.comcompass needle gets deflected when thecurrent flows in a nearby wire. Can youconnect the two observations? When thecurrent flows through a wire, does thewire behave like a magnet?This is what a scientist called HansChristian Oersted (Fig. 14.18) alsowondered. He was the first person whonoticed the deflection of compass needleevery time the current was passedthrough the wire.So, when electric current passesthrough a wire, it behaves like a magnet.This is the magnetic effect of the electriccurrent. In fact, an electric current canbe used to make magnets. Do you findit too surprising? Let us try it out.14.4 ELECTROMAGNETActivity 14.6Take around 75 cm long piece ofinsulated (plastic or cloth covered orenamelled) flexible wire and an iron nail,say about 6–10 cm long. Wind the wiretightly around the nail in the form of acoil. Connect the free ends of the wireFig. 14.19 An electromagnetRemember not to switch on thecurrent for more than a few secondsat a time. The electromagnet weakensthe cell quickly if left connected.to the terminals of a cell through a switchas shown in Fig 14.19.Place some pins on or near the endof the nail. Now switch on the current.What happens? Do the pins cling to thetip of the nail? Switch off the current.Are the pins still clinging to the end ofthe nail?The coil in the above activity behaveslike a magnet when electric current flowsthrough it. When the electric current isswitched off, the coil generally loses itsmagnetism. Such coils are calledelectromagnets. The electromagnetscan be made very strong and can liftvery heavy loads. Do you remember thecrane about which you read in Chapter 13of Class VI? The end of such a cranehas a strong electromagnet attached toit. The electromagnets are also used toseparate magnetic material from thejunk. Doctors use tiny electromagnetsto take out small pieces of magneticmaterial that have accidentally fallen inthe eye. Many toys also haveelectromagnets inside them.14.5 ELECTRICBELLWe are quite familiar with an electric bell.It has an electromagnet in it. Let us seehow it works.Fig. 14.20 shows the circuit of anelectric bell. It consists of a coil of wirewound on an iron piece. The coil acts168SCIENCE

www.GOALias.blogspot.comas an electromagnet. An iron strip witha hammer at one end is kept close tothe electromagnet. There is a contactscrew near the iron strip. When the ironstrip is in contact with the screw, thecurrent flows through the coil whichbecomes an electromagnet. It, then,Fig. 14. 20 Circuit of an electric bellpulls the iron strip. In the process, thehammer at the end of the strip strikesthe gong of the bell to produce a sound.However, when the electromagnet pullsthe iron strip, it also breaks the circuit.The current through the coil stopsflowing. Will the coil remain anelectromagnet?The coil is no longer an electromagnet.It no longer attracts the iron strip. Theiron strip comes back to its originalposition and touches the contact screwagain. This completes the circuit. Thecurrent flows in the coil and thehammer strikes the gong again. Thisprocess is repeated in quick succession.The hammer strikes the gong every timethe circuit is completed. This is howthe bell rings.KeywordsBatteryElectric componentsCircuit diagramWhat you have learntElectric bellElectromagnetFuseHeating effectMagnetic effect• It is convenient to represent electric components by symbols. Using these,an electric circuit can be represented by a circuit diagram.• When an electric current flows through a wire, the wire gets heated. It isthe heating effect of current. This effect has many applications.• Wires made from some special materials melt quickly and break whenlarge electric currents are passed through them. These materials areused for making electric fuses which prevent fires and damage to electricappliances.• When an electric current flows through a wire, it behaves like a magnet.• A current carrying coil of an insulated wire wrapped around a piece ofiron is called an electromagnet.• Electromagnets are used in many devices.169ELECTRICCURRENTAND ITS EFFECTS169

www.GOALias.blogspot.comExercises1. Draw in your notebook the symbols to represent the followingcomponents of electrical circuits: connecting wires, switch in the ‘OFF’position, bulb, cell, switch in the ‘ON’ position, and battery2. Draw the circuit diagram to represent the circuit shown in Fig.14.21.Fig. 14.213. Fig.14.22 shows four cells fixed on a board. Draw lines to indicate howyou will connect their terminals with wires to make a battery of fourcells.Fig. 14.224. The bulb in the circuit shown in Fig.14.23 does not glow. Can youidentify the problem? Make necessary changes in the circuit to makethe bulb glow.Fig. 14.235. Name any two effects of electric current.170SCIENCE

www.GOALias.blogspot.com6. When the current is switched on through a wire, a compass needle keptnearby gets deflected from its north-south position. Explain.7. Will the compass needle show deflection when the switch in the circuitshown by Fig.14.24 is closed?8. Fill in the blanks:Fig. 14.24(a) Longer line in the symbol for a cell represents its terminal.(b) The combination of two or more cells is called a .(c) When current is switched ‘on’ in a room heater, it .(d)The safety device based on the heating effect of electric current iscalled a .9. Mark ‘T’ if the statement is true and ‘F’ if it is false:(a)(b)(c)(d)To make a battery of two cells, the negative terminal of one cell isconnected to the negative terminal of the other cell. (T/F)When the electric current through the fuse exceeds a certain limit,the fuse wire melts and breaks. (T/F)An electromagnet does not attract a piece of iron. (T/F)An electric bell has an electromagnet. (T/F)10. Do you think an electromagnet can be used for separating plastic bagsfrom a garbage heap? Explain.11. An electrician is carrying out some repairs in your house. He wants toreplace a fuse by a piece of wire. Would you agree? Give reasons foryour response.12. Zubeda made an electric circuit using a cell holder shown in Fig. 14.4,a switch and a bulb. When she put the switch in the ‘ON’ position, thebulb did not glow. Help Zubeda in identifying the possible defects in thecircuit.171ELECTRICCURRENTAND ITS EFFECTS171

www.GOALias.blogspot.com13. In the circuit shown in Fig. 14.25A B CFig. 14.25(i)(ii)Would any of the bulb glow when the switch is in the ‘OFF’position?What will be the order in which the bulbs A, B and C will glowwhen the switch is moved to the ‘ON’ position?Extended Learning — Activities and Projects1. Set up the circuit shown in Fig. 14.17 again. Move the key to ‘ON’position and watch carefully in which direction the compass needlegets deflected. Switch ‘OFF’ the current. Now keeping rest of the circuitintact, reverse the connections at the terminal of the cell. Again switch‘on’ the current. Note the direction in which the needle gets deflected.Think of an explanation.2. Make four electromagnets with 20, 40, 60 and 80 turns. Connect themone by one to a battery of 2 cells. Bring the electromagnet near a box ofpins. Count the number of pins attracted by it. Compare the strengthsof the electromagnets.Paheli and Boojho saw a magic trick sometime back. The magician placedan iron box on a stand. He then called Boojho and asked him to lift thebox. Boojho could easily lift the box. Now the magician made a show ofmoving his stick around the box while muttering some thing. He againasked Boojho to lift the box. This time Boojho could not even move it. Themagician again muttered some thing and now Boojho could lift the box.The audience, including Paheli and Boojho, were very impressed withthe show and felt that the magician had some supernatural powers.However, after reading this chapter Paheli is wondering if the trick wasindeed some magic or some science was involved? Can you guess whatscience might be involved?172SCIENCE

www.GOALias.blogspot.com3. Using an electromagnet, you can make a working model of a railwaysignal as shown in Fig.14.26.ThreadCardboard signalIron nailCoilFig. 14.26 A working model of a railway signal4. Visit an electric shop. Request a mechanic to show you the varioustypes of fuses and MCB and to explain how they work.You can read more on the following website:www.glenbrook.k12.il.us/gbssci/phys/class/circuits/u9l2a.htmlDid You Know?The credit for the invention of the electric bulbis usually given to Thomas Alva Edison, thoughothers before him had worked on it. Edisonwas a remarkable man. He made some 1300inventions including the electric bulb,gramophone, the motion picture camera andthe carbon transmitter, which facilitated theinvention of the telephone.Fig. 14.27 Thomas Alva Edison(A.D. 1847 – 1931)173ELECTRICCURRENTAND ITS EFFECTS173

www.GOALias.blogspot.com1515 LightYou might have seen a beam ofsunlight when it enters a roomthrough a narrow opening or a hole.You may have also seen beams of light fromthe headlamps of scooters, cars and enginesof trains [Fig. 15.1 (a)]. Similarly, a beamof light can be seen from a torch. Some of(a) Rail engineFig. 15.1 Beams of lightyou may have seen a beam of searchlightfrom a light house or from an airporttower [Fig. 15.1 (b)].What do these experiences suggest?15.1(b) Light house15.1 LIGHTTRAVELSALONG ASTRAIGHTLINEBoojho recalls an activity he performedin Class VI. In that activity he looked(a)(b)Fig. 15.2 Looking at a candle through a straight and a bent pipe174SCIENCE

www.GOALias.blogspot.comFig. 15.3 Reflection of objects in waterat a lighted candle first througha straight pipe and then througha bent pipe (Fig. 15.2). Why wasBoojho not able to see the candleflame through a bent pipe?This activity showed thatlight travels along straight lines.How can we change the pathof light? Do you know, whathappens when light falls on apolished or a shiny surface?15.2 REFLECTIONOF LIGHTOne way to change the directionof light is to let it fall on a shinysurface. For example, a shiningstainless steel plate or a shiningsteel spoon can change thedirection of light. The surface ofwater can also act like a mirrorand change the path of light.Have you ever seen the reflectionof trees or buildings in water(Fig. 15.3)?Any polished or a shiny surface canact as a mirror. What happens whenlight falls on a mirror?You have learnt in Class VI that amirror changes the direction of light thatfalls on it. This change of direction by amirror is called reflection of light. Canyou recall the activity in which you gotthe light of a torch reflected from amirror? Let us perform a similar activity.Activity 15.1Take a torch. Cover its glass with a chartpaper which has three slits as shown inFig. 15.5. Spread a sheet of chart paperPaheli remembers the story of the lion and therabbit from the Panchtantra, in which therabbit fooled the lion by showing him hisreflection in water (Fig. 15.4).Fig. 15.4 Reflection of the lion in water175LIGHT175

www.GOALias.blogspot.comsee the slits in the mirror? This is theimage of the slits.This activity shows how light getsreflected from a plane mirror.Let us play around with the imagesformed in mirrors and know a little moreabout them.Activity 15.2Fig. 15.5 Reflection of light from a mirroron a smooth wooden board. Fix a planemirror strip vertically on the chart paper(Fig. 15.5). Now direct the beam of lighton the mirror from the torch with slits.Place the torch in such a way that itslight is seen along the chart paper onthe board. Now adjust its position sothat the light from the torch strikes theplane mirror at an angle (Fig. 15.5).Does the mirror change the directionof light that falls on it? Now move thetorch slightly to either side. Do you findany change in the direction of reflectedlight?Look into the mirror along thedirection of the reflected light. Do youCAUTIONHandle the lighted candle with care.It is better if this activity is performedin the presence of a teacher or an elderperson.Place a lighted candle in front of aplane mirror. Try to see the flame of thecandle in the mirror. It appears as if asimilar candle is placed behind themirror. The candle, which appearsbehind the mirror, is the image of thecandle formed by the mirror (Fig. 15.6).The candle itself is the object.Now move the candle to differentpositions in front of the mirror. Observethe image in each case.Paheli wants to know, whatmakes things visible to us?Boojho thinks that objects arevisible only when light reflectedfrom them reaches our eyes. Doyou agree with him?Fig. 15.6 Image of a candle in a plane mirror176SCIENCE

www.GOALias.blogspot.comBoojho noted in his notebook: Isit not surprising that my image isof the same size as me whetherthe mirror is small or large?Was the image upright in each case?Did the flame appear on top of the candleas in the object? Such an image is callederect. An image formed by a planemirror is erect and of the same size asthe object.Now place a vertical screen behindthe mirror. Try to obtain the image ofthe candle on this screen. Can you getthe image on the screen? Now place thescreen in front of the mirror. Can youget the image on the screen now? Youwill find that the image of the candlecannot be obtained on the screen ineither case.What about the distance of the imagefrom mirror? Let us perform anotheractivity.Activity 15.3Take a chess board. If a chess board isnot available, draw on a chart paper 64(88) squares of equal size. Draw a thickline in the middle of the paper. Fix aplane mirror vertically on this line. Placeany small object, such as a pencilsharpner, at the boundary of the thirdsquare counting from the mirror(Fig. 15.7). Note the position of theimage. Now shift the object to theboundary of the fourth square. Againnote the position of the image. Did youfind any relation between the distanceof the image from the mirror and that ofthe object in front of it?Fig. 15.7 Locating image in a plane mirrorPaheli made a note in her notebook:In a plane mirror the image isformed behind the mirror. It is erect,of the same size and is at the samedistance from the mirror as theobject is in front of it.You will find that the imageis at the same distance behindthe mirror as the object is in frontof it. Now verify this by placingthe object anywhere on the chartpaper.177LIGHT177

www.GOALias.blogspot.com15.3 R15.3 RIGHTOR LEFTEFT!When you see your image in a planemirror, is it exactly like you? Have youever noticed that there is one interestingdifference between you and your imagein a mirror? Let us find out.Activity 15.4Stand in front of a plane mirror and lookat your image. Raise your left hand.Which hand does your image raise(Fig. 15.8)? Now touch your right ear.Which ear does your hand touch in yourimage? Observe carefully. You will findthat in the mirror the ‘right’ appears ‘left’and the ‘left’ appears ‘right’. Note thatonly sides are interchanged; the imagedoes not appear upside down.Now write down your name on a pieceof paper and hold it in front of a planeFig. 15.9 An ambulancemirror. How does it appear in themirror?Boojho saw an ambulance onthe road. He was surprised tosee that the word ‘AMBULANCE’in front was written in a strangemanner.Fig. 15.8 Left hand appears on the right side inthe imageCan you now understandwhy the word ‘AMBULANCE’ is writtenas in Fig. 15.9 ? When the driver of avehicle ahead of an ambulance looks inher/his rear view mirror, s/he can read‘AMBULANCE’ written on it and giveway to it. It is the duty of every one ofus to allow an ambulance to passwithout blocking its way.You might have observed that in theside mirror of a scooter or a car theimages of all the objects appear smallerthan the objects themselves. Have youever wondered why it is so?178SCIENCE

www.GOALias.blogspot.com15.4 P15.4 PLAYINGWITH SPHERICALMIRRORSPaheli and Boojho were waiting for theirdinner. Boojho lifted a stainless steelplate and saw his image in it. Oh! Thisplate acts as a plane mirror. My imageis erect and is of the same size. Pahelisaw her image using the back of a steelspoon. “Boojho look here! I can also seemy erect image though it is smaller insize. This spoon also acts as a mirror ofsome kind”, said Paheli.You can also use a spoon or anycurved shining surface to see yourimage.Activity 15.5Take a stainless steel spoon. Bring theouter side of the spoon near your faceand look into it. Do you see your imagein it (Fig. 15.10)? Is this image differentfrom what you see in a plane mirror? Isthis image erect? Is the size of the imagethe same, smaller or larger?Now look at your image using theinner side of the spoon. This time youmay find that your image is erect andlarger in size. If you increase the distanceof the spoon from your face, you maysee your image inverted (Fig. 15.11). Youcan also compare the image of your penor pencil instead of your face.Fig. 15.11 Image from the inner side of a spoonThe curved shining surface of aspoon acts as a mirror. The mostcommon example of a curved mirror isa spherical mirror.If the reflecting surface of a sphericalmirror is concave, it is called a concavemirror. If the reflecting surface is convex,then it is a convex mirror (Fig. 15.12).(a)(b)Fig. 15.10 Image from the outer side of a spoonFig. 15.12 A concave and a convex mirror179LIGHT179

www.GOALias.blogspot.comWhy are concave and convex mirrorscalled spherical mirrors?Take a rubber ball and cut aportion of it with a knife or a hacksawblade [Fig. 15.13 (a)]. (Be careful.Ask an elder person to help you incutting the ball). The inner surfaceof the cut ball is called concave andthe outer surface is called convex(Fig. 15.13 (b)).Convex surface(a)Fig. 15.13 A spherical mirror is a part of asphereThe inner surface of a spoon acts likea concave mirror, while its outer surfaceacts like a convex mirror.We know that the image of an objectformed by a plane mirror cannot beobtained on a screen. Let us investigateif it is also true for the image formed bya concave mirror.Activity 15.6CAUTIONConvex surface(b)You will conduct Activity 15.6 in thesunlight. Be careful, never lookdirectly towards the sun or its imageas it may damage your eyes. You maylook at the image of the sun when itis thrown on a screen or a wall.Fig. 15.14 A concave mirror forms a real imageof the sunTake a concave mirror. Hold it facingthe sun. Try to get the light reflected bythe mirror on a sheet of paper. Adjustthe distance of the paper until you get asharp bright spot on it (Fig. 15.14). Holdthe mirror and the sheet of paper steadyfor a few minutes. Does the paper startburning?This bright spot is, in fact, the imageof the sun. Notice that this image isformed on a screen. An image formedon a screen is called a real image.Recollect that in Activity 15.2 the imageformed by a plane mirror could not beobtained on a screen. Such an image iscalled a virtual image.Now let us try to obtain on the screenthe image of a candle flame formed by aconcave mirror.Activity 15.7Fix a concave mirror on a stand (anyarrangement to keep the mirror steadywould do) and place it on a table(Fig. 15.15). Paste a piece of white paperon a cardboard sheet (say about180SCIENCE

www.GOALias.blogspot.comFig. 15.15 Real images formed by a concave mirror15cm10cm). This will act as a screen.Keep a lighted candle on the table at adistance of about 50 cm from the mirror.Try to obtain the image of the flame onthe screen. For this, move the screen tilla sharp image of the flame is obtained.Make sure that, the screen does notFig. 15.16 Virtual image formed by a concavemirrorobstruct the light from the candle fallingon the mirror. Is this image real orvirtual? Is it of the same size as the flame?Now move the candle towards themirror and place it at different distancesfrom it. In each case try to obtain theimage on the screen. Record yourobservation in Table 15.1. Is it possibleto obtain the image on the screen whenthe candle is too close to the mirror(Fig. 15.16)?We see that the image formed by aconcave mirror can be smaller or largerin size than the object. The image mayalso be real or virtual.Concave mirrors are used for manypurposes. You might have seen doctorsusing concave mirrors for examiningeyes, ears, nose and throat. Concavemirrors are also used by dentiststo see an enlarged image of the teeth(Fig. 15.17). The reflectors of torches,headlights of cars and scooters areconcave in shape (Fig. 15.18).181LIGHT181

www.GOALias.blogspot.comFig. 15.17 A dentist examining a patientBoojho observed his image in theshiny surface of the bell on his newbicycle. He found that his image waserect and smaller in size. He wonderedif the bell is also a kind of sphericalmirror. Can you recognise the type ofthe mirror?Note that the reflecting surface of thebell is convex.Activity 15.8Repeat Activity 15.7 now with a convexmirror in place of a concave mirror(Fig. 15.19). Record your observationsin a Table similar to Table 15.1.Could you get a real image at anydistance of the object from the convexConcave surfaceFig. 15.18 Reflector of a torchFig. 15.19 Image formed by a convex mirrorTable 15.1 Image formed by a concave mirror for objectplaced at different distances from itDistance of the object fromSmaller/larger Character of the imagethe mirrorthan the objectInverted/ erectReal/virtual50 cm … …40 cm … …30 cm20 cm10 cm …5 cm182SCIENCE

www.GOALias.blogspot.comFig. 15.20 Convex mirror as side view mirrormirror? Did you get an image larger insize than the object?Can you now recognise the mirrorsused as side mirrors in scooters? Theseare convex mirrors. Convex mirrors canform images of objects spread over a largearea. So, these help the drivers to seethe traffic behind them (Fig. 15.20).15.5 IMAGESFORMEDBY LENSESYou might have seen a magnifying glass.It is used to read very small print(Fig. 15.21). You might have also usedit to observe the body parts of acockroach or an earthworm. Themagnifying glass is actually a type of a lens.Lenses are widely used in spectacles,telescopes and microscopes. Try to adda few more uses of lenses to this list.Get some lenses. Touch and feelthem. Can you find some difference justby touching? Those lenses which feelthicker in the middle than at the edgesare convex lenses [Fig. 15.22 (a)]. ThoseFig. 15.21 A magnifying glasswhich feel thinner in the middle thanat the edges are concave lenses[Fig. 15.22 (b)]. Notice that the lensesare transparent and light can passthrough them.(a)Fig. 15.22 (a) A convex lens and (b) a concavelensLet us play with lenses.CAUTION(b)It is dangerous to look through a lensat the sun or a bright light. You shouldalso be careful not to focus sunlightwith a convex lens on any part of yourbody.183LIGHT183

www.GOALias.blogspot.comActivity 15.9Take a convex lens or magnifying glass.Put it in the path of sunrays. Place asheet of paper as shown (Fig. 15.23).Adjust the distance between the lens andthe paper till you get a bright spot onthe paper. Hold the lens and the paperin this position for a few minutes. Doesthe paper begin to burn?Now replace the convex lens with aconcave lens. Do you see a bright spotA convex lens converges (bendsinward) the light generally falling on it[Fig. 15.24 (a)]. Therefore, it is called aconverging lens. On the other hand, aconcave lens diverges (bends outward)the light and is called a diverging lens[Fig. 15.24 (b)].(a)(b)Fig. 15.24Fig. 15.23 Real image of the sun by a convexlenson the paper this time, too? Why areyou not getting a bright spot this time?We have seen in the case of mirrorsthat for different positions of the objectthe nature and size of the image change.Is it true for lenses also?Let us find out.Activity 15.10Take a convex lens and fix it on a standas you did with the concave mirror. Placeit on a table. Place a lighted candle at adistance of about 50 cm from the lens[Fig. 15.25 (a)]. Try to obtain the image184of the candle on a paper screen placedon the other side of the lens. You mayhave to move the screen towards or awayfrom the lens to get a sharp image ofthe flame. What kind of image did youget? Is it real or virtual?Now vary the distance of the candlefrom the lens [Fig. 15.25 (b)]. Try toobtain the image of the candle flameevery time on the paper screen bymoving it. Record your observations asyou did in Activity 15.7 for the concavemirror.It means that we can see theimage formed by a lense from theside opposite to that of the object.SCIENCE

www.GOALias.blogspot.com(a)(b)Fig. 15.25 Image by a convex lens for object placed at different distance from itFig. 15.26 Virtual image formed bythe convex lensFig. 15.27 Image formed by a concave lensDid you get in any position of theobject an image which was erect andmagnified (Fig. 15.26). Could this imagebe obtained on a screen? Is the imagereal or virtual? This is how a convex lensis used as a magnifying glass.In a similar fashion study the imagesformed by a concave lens. You will findthat the image formed by a concave lensis always virtual, erect and smaller insize than the object (Fig. 15.27).15.6 SUNLIGHT— WHITEORCOLOUREDOLOURED?Have you ever seen a rainbow in thesky? You might have noticed that itappears usually after the rain when thesun is low in the sky. The rainbow is185LIGHT185

www.GOALias.blogspot.comFig. 15.29 A CD placed in sunFig. 15.28 A rainbowseen as a large arc in the sky with manycolours (Fig. 15.28).How many colours are present in arainbow? When observed carefully, thereare seven colours in a rainbow, thoughit may not be easy to distinguish all ofthem. These are — red, orange, yellow,green, blue, indigo and violet.Does this mean that thewhite light consists ofseven colours?You might have seen that when youblow soap bubbles, they appearcolourful. Similarly, when light isreflected from the surface of aCompact Disk (CD), you see manycolours (Fig. 15.29).On the basis of these experiences,could we say that the sunlight is amixture of different colours? Let usinvestigate.Activity 15.11Take a glass prism. Allow a narrow beamof sunlight through a small hole in thewindow of a dark room to fall on oneface of the prism. Let the light comingout of the other face of the prism fall onPaheli wants to tell youthat you can see arainbow only when yourback is towards the sun.Fig. 15.30 A prism splits sunlight into seven colours186SCIENCE

www.GOALias.blogspot.coma white sheet of paper or on a white wall.What do you observe? Do you see colourssimilar to those in a rainbow (Fig.15.30)? This shows that the sunlightconsists of seven colours. The sunlightis said to be white light. This means thatthe white light consists of seven colours.Try to identify these colours and writetheir names in your notebook.Can we mix these colours to get whitelight? Let us try.Activity 15.12Take a circular cardboard disc of about10 cm diameter. Divide this disc intoseven segments. Paint the sevenrainbow colours on these segmentsas shown in Fig. 15.31 (a). You canalso paste, coloured papers onthese segments. Make a small holeat the centre of the disc. Fix thedisc loosely on the tip of a refill of aball pen. Ensure that the disc rotatesfreely [Fig. 15.31 (a)]. Rotate the discin the daylight. When the disc isrotated fast, the colours get mixedtogether and the disc appearsto be whitish [Fig. 15.31 (b)]. Sucha disc is popularly known as Newton’sdisc.Fig. 15.31 (a) A disc with seven colours (b) It appears white on rotatingPaheli has a brilliant idea! Shehas prepared a small top witha small circular disc withseven rainbow colourspainted on it (Fig. 15.32).When the top rotates itappears nearly white.Fig. 15.32 A top with seven colours187LIGHT187

www.GOALias.blogspot.comKeywordsConcave lensConcave mirrorConvex lensConvex mirrorErect imageMagnified imageMagnifying glassPrismRainbowReal imageRear view mirrorSide mirrorSpherical mirrorVirtual imageWhat you have learnt• Light travels along straight lines.• Any polished or a shining surface acts as a mirror.• An image which can be obtained on a screen is called a real image.• An image which cannot be obtained on a screen is called a virtual image.• The image formed by a plane mirror is erect. It is virtual and is of thesame size as the object. The image is at the same distance behind themirror as the object is in front of it.• In an image formed by a mirror, the left side of the object is seen on theright side in the image, and right side of the object appears to be on theleft side in the image.• A concave mirror can form a real and inverted image. When the object isplaced very close to the mirror, the image formed is virtual, erect andmagnified.• Image formed by a convex mirror is erect, virtual and smaller in sizethan the object.• A convex lens can forms real and inverted image. When the object isplaced very close to the lens, the image formed is virtual, erect andmagnified. When used to see objects magnified, the convex lens is calleda magnifying glass.• A concave lens always forms erect, virtual and smaller image than theobject.• White light is composed of seven colours.188SCIENCE

www.GOALias.blogspot.comExercises1. Fill in the blanks:(a) An image that cannot be obtained on a screen is called____________.(b) Image formed by a convex __________ is always virtual and smallerin size.(c) An image formed by a __________ mirror is always of the same sizeas that of the object.(d) An image which can be obtained on a screen is called a _________image.(e) An image formed by a concave ___________ cannot be obtained ona screen.2. Mark ‘T’ if the statement is true and ‘F’ if it is false:(a) We can obtain an enlarged and erect image by a convex mirror. (T/F)(b) A concave lens always form a virtual image. (T/F)(c) We can obtain a real, enlarged and inverted image by a concavemirror. (T/F)(d) A real image cannot be obtained on a screen. (T/F)(e) A concave mirror always form a real image. (T/F)3. Match the items given in Column I with one or more items of Column II.Column IColumn II(a) A plane mirror (i) Used as a magnifying glass.(b) A convex mirror (ii) Can form image of objectsspread over a large area.(c) A convex lens (iii) Used by dentists to seeenlarged image of teeth.(d) A concave mirror (iv) The image is always invertedand magnified.(e) A concave lens (v) The image is erect and of thesame size as the object.(vi) The image is erect and smallerin size than the object.4. State the characteristics of the image formed by a plane mirror.5. Find out the letters of English alphabet or any other language known toyou in which the image formed in a plane mirror appears exactly likethe letter itself. Discuss your findings.189LIGHT189

www.GOALias.blogspot.com6. What is a virtual image? Give one situation where a virtual image isformed.7. State two differences between a convex and a concave lens.8. Give one use each of a concave and a convex mirror.9. Which type of mirror can form a real image?10. Which type of lens forms always a virtual image?Choose the correct option in questions 11–1–131311. A virtual image larger than the object can be produced by a(i) concave lens (ii) concave mirror(iii) convex mirror (iv) plane mirror12. David is observing his image in a plane mirror. The distance betweenthe mirror and his image is 4 m. If he moves 1 m towards the mirror,then the distance between David and his image will be(i) 3 m (ii) 5 m(iii) 6 m (iv) 8 m13. The rear view mirror of a car is a plane mirror. A driver is reversing hiscar at a speed of 2 m/s. The driver sees in his rear view mirror theimage of a truck parked behind his car. The speed at which the image ofthe truck appears to approach the driver will be(i) 1 m/s (ii) 2 m/s(iii) 4 m/s (iv) 8 m/sExtended Learning — Activities and Projects1. Play with a mirrorWrite your name with asketch pen on a thin sheetof paper, polythene or glass.Read your name on the sheetwhile standing in front of aplane mirror. Now look atyour image in the mirror.2. A burning candle in waterTake a shoe box, open on oneside. Place a small lightedcandle in it. Place a clearglass sheet (roughly 25 cm25 cm) infront of this candle(Fig. 15.33). Try to locate theimage of the candle behind Fig. 15.33 Candle burning in water190SCIENCE

www.GOALias.blogspot.comthe glass sheet. Place a glass of water at its position. Ask your friends tolook at the image of the candle through the sheet of glass. Ensure thatcandle is not visible to your friends. Your friends will be surprised to seethe candle burning in water. Try to explain the reason.3. Make a rainbowTry to make your own rainbow. You can try this project in the morningor in the evening. Stand with your back towards the sun. Take a hosepipeor a water pipe used in the garden. Make a fine spray in front of you.You can see different colours of rainbow in the spray.4. Visit a laughing gallery in some science centre or a science park or avillage mela. You will find some large mirrors there. You can see yourdistorted and funny images in these mirrors. Try to find out the kind ofmirrors used there.5. Visit a nearby hospital. You can also visit the clinic of an ENTspecialist, or a dentist. Request the doctor to show you the mirrors usedfor examining ear, nose, throat and teeth. Can you recognise the kind ofmirror used in these instruments?6. Role playHere is a game that a group of children can play. One child will bechosen to act as object and another will act as the image of the object.The object and the image will sit opposite to each other. The object willmake movements, such as raising a hand, touching an ear, etc. Theimage will have to make the correct movement following the movementof the object. The rest of the group will watch the movements of theimage. If the image fails to make the correct movement, she/he will beretired. Another child will take her/his place and the game willcontinue. A scoring scheme can be introduced. The group that scoresthe maximum will be declared the winner.You can read more on the following websites:www.glenbrook.k12.il.us/gbssci/phys/mmedia/optics/ifpm.htmlwww.glenbrook.k12.il.us/gbssci/phys/class/refln/u13l1b.html191LIGHT191

www.GOALias.blogspot.comDid you know?The mirrors can be used as weapons. Archimedes, a Greek scientist, is saidto have done just that more than two thousand years ago. When theRomans attacked Syracuse, a coastal city-state in Greece, Archimedes usedmirrors arranged as shown in Fig. 15.34. The mirrors could be moved in anydirection. They were positioned such that they reflected the sunlight on theRoman soldiers. The soldiers were dazzled by the sunlight. They did notknow what was happening. They got confused and ran away. This was anexample of triumph of ideas over military might.Fig. 15.34 Archimedes mirrors192SCIENCE

www.GOALias.blogspot.com1616 Water: A Precious Resource“Jal Hai, To Kal Hai ”“If you have water, you can think of the future”You are perhaps aware that 22 March iscelebrated as the world water day! Aschool celebrated ‘water day’ and invitedposters from the children of your agegroup. Some of the posters presentedon that day are shown in Fig. 16.1.Fig. 16.1 Collage of postersWhat is the message you get fromthese posters? Write your observationsin your notebook and discuss them inthe class.Have you ever felt a shortage of waterat home or at school? Your parents orteachers must very often be advising younot to waste water. No wonder wecelebrate water day every year to attractthe attention of everybody towards theimportance of conserving water.The amount of water recommendedby the United Nations for drinking,washing, cooking and maintaining properhygiene is a minimum of 50 litres perperson per day. This amount is abouttwo and a half buckets of water perperson per day. Is your family getting atleast this much of water? If yes, youshould consider yourself fortunatebecause millions of people in ourcountry do not get enough water. Whatabout your friends and their families?Share your experience with them.In some places there is an acuteshortage of water. Taps running dry,long queues for water (Fig. 16.2), fights,marches and protests for demand ofwater have become a common sight,especially during summers. Some of thenewspaper clippings shown in Fig. 16.3clearly indicate this message. Is it nottrue that we face acute shortage ofwater?

www.GOALias.blogspot.comFig. 16.2 Long queue for waterActivity 16.1Collect clippings from newspapers andmagazines on the news items, articlesand pictures related to water shortage.Paste them in your scrapbook and shareit with your friends. List some problemsfaced by the people and discuss themin the class.Water shortage has become a matterof concern throughout the world. It isestimated that in a few years from nowFig. 16.4 Earth appears blue from spaceFig. 16.3 Newspaper clippingsYear 2003 was observed asthe International Year ofFreshwater to make peopleaware of this dwindling natural resource.more than one third of the people inthe world could face water scarcity.Before we discuss why water isgetting scarce we must know how muchwater is available for use on our planet.16.1 HOWMUCH WATERIS AVAILABLELook at the picture of the earth takenfrom space. Why does it appear blue?Surely, you can guess!You are aware that about 71% ofthe earth’s surface is covered withwater. Almost all the water on theearth is contained in the seas andoceans, rivers, lakes, ice caps, asgroundwater and in the atmosphere.However, most of this water is not fit forhuman consumption. The water that isfit for use is freshwater. Perform the194SCIENCE

www.GOALias.blogspot.comfollowing activity to estimate roughlythe relative amount of water availablein some of these sources.Activity 16.2Most of us assume water to be a limitlessresource. From this activity can youStepsFigureRemarkTake a medium-sized bucketand fill it up with water. Itcontains about twenty litres ofwater.Assume that this waterrepresents all the water presenton the earth.Take a tea spoon of about 5 mLcapacity and transfer 100spoons of water from the bucketto a small container, like a bathmug.This represents totalfreshwater on the earth.From the bath mug transferthirty spoons of water to a glasstumbler.This gives a measure of usablewater present as groundwater.Finally take out a quarter (1/4 th )spoonfull of water from the mug.It represents all the waterpresent in all the lakes andrivers of the world.• The water left in the bucket represents the saline water present in the seas,oceans and partly as groundwater. This water is not fit for human use.• The water left in the bath mug represents the water, which is present in thefrozen form in glaciers, ice caps and permanent snow; again not available readily.Boojho wondered about thealarmingly small quantity ofwater available for our use.Paheli quickly calculated andfound that this amount isroughly 0.006% of all waterfound on the earth.ATER: : A PRECIOUSWATERATER195RECIOUS RESOURCE195

www.GOALias.blogspot.comappreciate the actual amount of wateravailable for human use? Does thefinding worry you? Discuss this in yourclass.16.2 F16.2 FORMSOF WATERAre you afraid that continuous use willsome day exhaust all the water availablefor use? You know that water on theearth has been maintained for millionsof years by various processes whichmake the water cycle. You have studiedthe water cycle in Class VI. Write in yourown words what you know about thewater cycle.You know that when water circulatesthrough the water cycle it can be foundin all the three forms, i.e., solid, liquidand gas — at any given time somewhereon the earth. The solid form, snow andice, is present as ice caps at the poles ofthe earth, snow-covered mountains andglaciers. Liquid water is present inoceans, lakes, rivers, and evenunderground. The gaseous form is thewater vapour present in the air aroundus. The continuous cycling of wateramong its three forms keeps the totalamount of water on the earth constanteven when the whole world is using it.Does it give you any relief?Can you recall the processes involvedin water cycle? The following activity willhelp you.Activity 16.3Fig. 16.5 shows the processes involvedin the water cycle. They are labelled bynumbers. Match these numbers withthe processes given in the jumbled form.Most towns and cities have watersupply system maintained by the civic4731. rudgon rawet2. atooniaervp3. acestoonnnid54. duclos25. tspratniaoinr66. aitfinlronit17. ntciepirtaipoFig. 16.5 Water cycle196SCIENCE

www.GOALias.blogspot.combodies. The water is drawn fromnearby lakes, rivers, ponds orwells. The water is suppliedthrough a network of pipes.Many villages do not have sucha water supply system. Therepeople fetch water directly fromthe sources. Often women andchildren have to walk severalkilometres to fetch water(Fig. 16.6). The children suffera lot. They cannot attendschool regularly since theyspend hours in fetching water.Women have toperform a number ofhousehold chores. If they havealso to spend time to fetch waterit adds to their burden.A large number of people draw waterfrom wells, tube wells or hand pumps.From where do these sources get water?16.3 GROUNDWATERAS AN IMPORTANTSOURCEOF WATERIf we dig a hole in the ground near awater body we may find that the soil ismoist. The moisture in the soil indicatesthe presence of water underground. Ifwe dig deeper and deeper, we wouldreach a level where all the space betweenparticles of soil and gaps between rocksare filled with water (Fig. 16.7). Theupper limit of this layer is called thewater table. The water table varies fromFig. 16.6 Women fetching waterplace to place, and it may even changeat a given place. The water table may beat a depth of less than a metre or maybe several metres below the ground. Thewater found below the water table iscalled groundwater. What is the sourceof this groundwater?The rainwater and water from othersources such as rivers and ponds seepsthrough the soil and fills the emptyspaces and cracks deep below theground. The process of seeping of waterinto the ground is called infiltration.The groundwater thus gets rechargedby this process. At places thegroundwater is stored between layers ofhard rock below the water table. This isknown as an aquifer. Water in theaquifers can be usually pumped out withthe help of tube wells or handpumps.Have you ever been to a site whereconstruction work is going on? FromATER: : A PRECIOUSWATERATER197RECIOUS RESOURCE197

www.GOALias.blogspot.comHand pumpRechargeStream or lakeWater tableAquiferGroundwaterFig. 16.7 Groundwater and water tablewhere do the workers get water forconstruction? May be you have seenboring being done at such sites to reachthe water table. Enquire from the peopleworking there how deep they have to dig.Can we keep on drawing water fromunder the ground? How will it affect thewater table?16.4 DEPLETIONOF WATERTABLEWater drawn from under the ground getsreplenished by seepage of rainwater. Thewater table does not get affected as longas we draw as much water as isreplenished by natural processes.However, water table may go down if thewater is not sufficiently replenished.This may happen due to many reasons.Increase in population, industrial and198agricultural activities are some commonfactors affecting water table. Scantyrainfall is another factor that maydeplete the water table. Yet anotherfactor affecting water table could bedeforestation and decrease in theeffective area for seepage of water.Increasing populationIncreasing population creates demandfor construction of houses, shops,offices, roads and pavements. Thisdecreases the open areas like parks, andplaygrounds. This, in turn, decreases theseepage of rainwater into the ground.What could be the consequence? Recallthat a pukka floor does not allow waterto seep in easily, while in a grass lawnwater seeps through in no time.SCIENCE

www.GOALias.blogspot.comMoreover a huge amount of water isrequired for construction work. Oftengroundwater is used for this purpose.So, on the one hand we areconsuming more groundwater, and onthe other we are allowing lesser waterto seep into the ground. This results indepletion of water table. In fact, thewater table in some parts of many citieshas gone down to alarmingly low levels.Increasing industriesWater is used by all the industries.Almost everything that we use needswater somewhere in its productionprocess. The number of industries isincreasing continuously. Water used bymost of the industries is drawn from theground.Activity 16.4Name some industries familiar to you.Make a list of the products obtainedfrom these and used in our daily life.Discuss with your teacher and parentshow the growing industrial activity isresponsible for the depletion of watertable.Agricultural activitiesA majority of farmers in India dependupon rains for irrigating their crops.Irrigation systems such as canals arethere only in a few places. Even thesesystems may suffer from lack of waterdue to erratic rainfall. Therefore, farmershave to use groundwater for irrigation.Population pressure on agricultureforces increasing use of groundwaterday by day. This results in depletion ofwater table.16.5 DISTRIBUTIONOF WATERThe distribution of water over the globeis quite uneven due to a number offactors.Some places have good amount ofrain and are water-rich. On the otherhand, there are deserts which havescanty rainfall.India is a vast country and therainfall is not the same everywhere.Some regions have excessive rains whilesome others have very little rainfall.Excessive rains cause floods, whereasthe absence of rains results in droughts.Therefore, some regions in our countrymay have floods while others may sufferfrom droughts at the same time.Activity 16.5Given here is the rainfall map of India(Fig. 16.8). It gives the average annualrainfall in different regions of our country.• Locate on the map the place you livein.• Are you blessed with sufficientrainfall?• Is there sufficient water available inyour area throughout the year?It may be possible that we are livingin an area where there is sufficientrainfall yet there is shortage of water. Canwe attribute this to mismanagement ofwater resources?16.6 WATERMANAGEMENTYou have read in Class VI that in manyplaces a regular supply of water isATER: : A PRECIOUSWATERATER199RECIOUS RESOURCE199

www.GOALias.blogspot.comFig. 16.8 Rain map of India1. Government of India, Copyright 2007.2. Based upon Survey of India map with the permission of the Surveyor General of India.3. The territorial waters of India extend into the sea to a distance of twelve nautical miles measured from the appropriate baseline.4. The external boundaries and coastlines of India agree with the Record/Master Copy certified by Survey of India.200SCIENCE

www.GOALias.blogspot.comprovided by a well-planned pipe system.When the civic authorities supply waterthrough pipes not all of it may reachthe destination. You might have seenwater supply pipes leaking and a lot ofwater gushing out of the pipes. It isthe responsibility of the civicauthorities to prevent such wastage ofprecious water.Mismanagement or wastage maytake place at the level of individuals also.All of us, knowingly or unknowingly,waste water while brushing teeth,shaving, bathing, washing and duringmany other activities. Leaking taps isanother source of huge water wastage.We waste water as though we do not needwater the next time!We have seen that most of the waterthat we get as rainfall just flows away.This is a waste of precious naturalresource. The rainwater can be used torecharge the groundwater. This isreferred to as water harvesting orrainwater harvesting, about which youhave learnt in Class VI.Find out if the buildings in yourneighbourhood have water harvestingsystems installed.We have at many places in India anage old practice of water storage andwater recharge like the bawris. Bawriwas the traditional way of collectingwater. With time the bawris fell intodisuse and garbage started piling in thesereservoirs. However, because of the acutewater shortage, people in these areashave had to rethink. The bawris are beingrevived. Today the situation is that inspiteof scanty rains these places aremanaging their water needs well.A farmer using water in the field canalso use water economically. Maybeyou have heard of drip irrigation(Fig. 16.9). Drip irrigation is a techniqueof watering plants by making use ofnarrow tubings which deliver waterdirectly at the base of the plant.A case studyBhujpur in the Kutch area of Gujarat has a very erratic rainfall. The only sourceof freshwater lies underground because rivers in this area do not have waterthroughout the year. Over the years, demand for water has grown. The withdrawalof groundwater has far exceeded recharge. As a result the water table has gonedown alarmingly.In 1989, the villagers along with a non-governmental organisation, decided toharvest rainwater. Eighteen check-dams were built on the Rukmavati river andits many tributaries. The water so collected increased percolation through thesoil and recharged the aquifers.According to farmers, the wells have water now and the water that flowed intothe sea and was wasted has become available for irrigation.ATER: : A PRECIOUSWATERATER201RECIOUS RESOURCE201

www.GOALias.blogspot.comWater-wise habits1. Turn off taps whilebrushing2. Mop the floor instead ofwashing16.7 WFig. 16.9 Drip irrigation in a field16.7 WHATROLEYOUCAN PLAYHave you ever shown concern if you sawa tap leaking in your house, school orany other place? Leaking taps waste alot of water. You must make efforts tostop this leakage.There are a number of ways you canadopt to minimise the wastage of water.Let us begin. We have given a fewexamples. Add on!16.8 E16.8 EFFECTOF WATERSCARCITYONPLANTSYou must have seen potted plantswilting and ultimately drying up if theydid not get water even for a few days.You have already learnt in Chapter 1that plants need water to get nutrientsfrom the soil to prepare their food. Justimagine the consequences if water is notavailable to plants!The green character of the planetshall be lost. This may mean the endof all life, for a world without plantsshall mean no food, no oxygen, notenough rain, and innumerable otherproblems.A successful initiativeRajasthan is a hot and dry place. The challenge of natural scarcity of water wasmet by a successful experiment. A band of social workers has transformed a dryarea in the Alwar district into a green place. They have revived five dried-uprivers — Arveri, Ruparel, Sarsa, Bhagani and Jahazwali by constructing waterharvestingstructures.KeywordsAquiferDepletionDrip irrigationGroundwaterInfiltrationRechargeWater harvestingWater table202SCIENCE

www.GOALias.blogspot.comWhat you have learnt• Water is essential for all living beings. There can be no life without it.• Water exists in three forms: solid, liquid and vapour.• Though water is maintained by the water cycle, yet there is an acutescarcity of water in many parts of the globe.• There is an uneven distribution of water. Much of it has resulted fromhuman activities.• Rapid growth of industries, increasing population, growing irrigationrequirements and mismanagement are some of the causes for watershortage.• We need to be worried about the wastage during the supply of waterthrough pipes, the leaking taps in buildings and other places.Unnecessary use of water and overdrawing from groundwater should beavoided. Recharge of water to the ground should be increased.• The need of the hour is that every individual uses water economically.• Plants wilt and ultimately dry-up if they are not watered for a few days.Exercises1. Mark ‘T’ if the statement is true and ‘F’ if it is false:(a)(b)(c)(d)The freshwater stored in the ground is much more than thatpresent in the rivers and lakes of the world. (T/F)Water shortage is a problem faced only by people living in ruralareas. (T/F)Water from rivers is the only source for irrigation in the fields. (T/F)Rain is the ultimate source of water. (T/F)2. Explain how groundwater is recharged?3. There are ten tubewells in a lane of fifty houses. What could be the longterm impact on the water table?4. You have been asked to maintain a garden. How will you minimise theuse of water?5. Explain the factors responsible for the depletion of water table.6. Fill in the blanks with the appropriate answers:(a) People obtain groundwater through________ and ________.ATER: : A PRECIOUSWATERATER203RECIOUS RESOURCE203

www.GOALias.blogspot.com(b) Three forms of water are ________, ________ and ________.(c) The water bearing layer of the earth is ________.(d) The process of water seepage into the ground is called ________.7. Which one of the following is not responsbile for water shortage?(i) Rapid growth of industries(ii) Increasing population(iii) Heavy rainfall(iv) Mismanagement of water resources8. Choose the correct option. The total water(i) in the lakes and rivers of the world remains constant.(ii) under the ground remains constant.(iii) in the seas and oceans of the world remains constant.(iv) of the world remains constant.9. Make a sketch showing groundwater and water table. Label it.Extended Learning — Activities and Projects1. Role playYou are a water detective in your school. You have a team of sixmembers. Survey the campus and make a note of the following:(a)Total number of taps(b) Number of taps leaking(c) Amount of water wasted due to leakage(d) Reasons of leakage(e) Corrective measures taken2. Groundwater pumped outTry to find out if there are any hand pumps in your neighbourhood. Goto the owner or the users of a few of these and find out the depth atwhich they struck water? If there are any differences, think of theprobable reason. Write a brief report and discuss it in your class. Ifpossible, visit a place where boring is going on to install a hand pump.Watch the process carefully and find out the depth of the water table atthat place.3. Catching rainwater — Traditional methodsForm groups of 4 to 5 students in the class and prepare a report on thevarious traditional ways of water harvesting. If possible, use thefollowing web link: www.rainwaterharvesting.org.204SCIENCE

www.GOALias.blogspot.com4. Conservation of waterCarrry out a campaign to conserve water at home and in the school.Design posters to remind others of the importance of water resources.5. Create a logoHold a competition to create a logo or a symbol depicting water scarcity.Did you know?The importance of water management has been highlighted by a watershedmanagement project near the village of Kothapally. The project has yieldeddramatic results. Groundwater levels have risen, green cover hasincreased, and productivity and incomes in this semi-arid region havedramatically improved.ATER: : A PRECIOUSWATERATER205RECIOUS RESOURCE205

www.GOALias.blogspot.com1717 Forests: Our LifelineOne evening Boojho entered thepark with an elderly person. Heintroduced him to his friends.Prof Ahmad was a scientist working inthe university. The children startedplaying while Prof Ahmad sat on abench in the corner. He was tired as hehad participated in the golden jubileecelebrations of the town. After a while,the children also came and sat aroundhim. They wanted to know about thecelebrations. Prof Ahmad told them thatafter the cultural programme, thesenior people discussed the town’sunemployment problem. A plan wasproposed to put up a factory by clearingan area of the forest just outside thetown. This would give the increasingpopulation of the town a chance to getjobs. The children were very surprisedwhen Prof Ahmad told them that manypeople had objected to this idea.Fig. 17.1 A view of a forest“This is because the forests serve asgreen lungs and water purifying systemsin nature”, Prof Ahmad explained. Thechildren were confused. Prof Ahmadrealised that the children had not visiteda forest. The children also wanted toknow more about the forest, so theydecided to visit it with Prof Ahmad.17.1 VISITTO A FORESTOne Sunday morning, the childrenpacked a few things like a knife, a handlens, a stick, a notebook and walkedtogether through a forest trail near avillage. On their way, they met Tibu, ayoung boy of their age group, of nearbyvillage, who was taking cattle for grazingalong with his aunt. He was very agile,running here and there to keep the herdtogether. When he saw the children,Tibu also started walking along withthem, while his aunt went on a differentpath. As soon as they entered the forestTibu raised his hand and signalled themto keep quiet because noise coulddisturb the animals living in the forest.Tibu then took them to a place at aheight to show them the broad view ofthe forest. Children were surprisedbecause they could not see any land(Fig. 17.1). The different treetops hadformed green cover over the land. However,the cover was not uniformly green. The206SCIENCE

www.GOALias.blogspot.comenvironment was peaceful and a coolbreeze was blowing. This made childrenquite fresh and happy.While coming down, they got excitedon hearing a sudden sound of birds andsome noise from the top branches of thetrees. Tibu told them to relax since itwas a normal phenomenon here.Because of the children’s presence, somemonkeys had climbed higher up on thetrees where they disturbed the birds.Animals often give this type of warningcall to alert other animals. Tibu also toldthat many other animals like boar,bison, jackals, porcupine, elephants livein the deeper areas of the forest(Fig. 17.2). Prof Ahmad cautionedchildren that they should not go deepinto the forest.Boojho and Paheli remembered thatthey have studied about forests asFig. 17.3 Forest as habitatan example of a habitat in Class VI(Fig. 17.3). They could see now how theforest provides a home for many animalsand plants.Fig. 17.2 Some forest animals: O207FORESTSORESTS: : OURLIFELINE207

www.GOALias.blogspot.comNeemSheeshamSemalFig. 17.4 Some forest plantsBamboooThe land where the children werewalking was uneven and covered withmany trees. Tibu helped them to identifysal, teak, semal, sheesham, neem,palash, fig, khair, amla, bamboo,kachnar (Fig. 17.4). Prof Ahmad pointedout that there are several other trees,shrubs, herbs and grasses in the forest.The trees were also covered with differenttypes of creepers and climbers. The sunwas barely visible through the leaves ofthe trees, making it quite dark insidethe forest.Activity 17.1Observe the various things in your homeand make a list of those which are madefrom material which may have beenobtained from the forest.You might have many wooden itemson your list like plywood, fuel wood,boxes, paper, matchsticks, andfurniture. Do you know that gum, oils,spices, fodder for animals and medicinalplants are also some of the productswhich we get from the forest (Fig. 17.5).208SCIENCE

www.GOALias.blogspot.comSheila wondered who would haveplanted these trees. Prof Ahmad repliedthat in nature trees produce enoughseeds. The forest floor providesfavourable conditions for them togerminate and develop into seedlingsSealing waxHoneyGumFig. 17.5 Forest productsWoodenstatueCatechuand saplings. Some grow up into trees.He added that branchy part of a treeabove the stem is known as the crownof the tree (Fig. 17.6).Prof Ahmad asked children to lookup and observe how the branches of thetall trees look like a roof over the otherplants in the forest. He told them thatthis is called a canopy (Fig. 17.7).Activity 17.2Visit a forest or a park in yourneighbourhood. Observe the trees andtry to identify them. You can take thehelp of some elders or books on trees.List the characteristics of the trees thatyou observe, such as the height, shapeof leaves, crown, flowers, and fruits. Alsodraw the crowns of some trees.Prof Ahmad pointed out that treeshad crowns of different types and sizes.These had created different horizontallayers in the forest. These are known asunderstoreys (Fig. 17.7). Giant and talltrees constituted the top layer followedby shrubs and tall grasses, and herbsformed the lowest layer.“Would we see similar kind of treesin every forest?” — asked Boojho.Prof Ahmad said, “No, due to differentclimatic conditions there are variationsin the types of trees and other plants.The types of animals also differ fromforest to forest.”Fig. 17.6 Some crown shapes: O209FORESTSORESTS: : OURLIFELINE209

www.GOALias.blogspot.comCanopyUnderstoreyA few children were busy watchingbeautiful butterflies fluttering here andthere on the flowers of shrubs andherbs. They had a close look at thebushes. While doing that their hair andclothes had seeds and shrubs clingingto them.They came across numerous insects,spiders, squirrels, ants and variousFig. 17.8 Forest floorFig. 17.7 Canopy and under storeys in a forestother small animals on the bark of thetrees, plant leaves and on decayingleaves on the forest floor (Fig. 17.8). Theystarted making sketches of thesecreatures. The forest floor seemed darkcoloured and was covered with a layerof dead and decaying leaves, fruits,seeds, twigs and small herbs. Thedecaying matter was moist and warm.Children picked up various seedsand leaves for their collection. Walkingover the dead leaf layer on the forest floorwas like walking over a spongy carpet!Is the decaying matter always warm?Prof Ahmad suggested that the childrencould perform an activity to get ananswer to this question.Activity 17.3Dig a small pit. Put vegetable waste andleaves in it. Cover them with soil. Addsome water. After three days, remove the210SCIENCE

www.GOALias.blogspot.comupper layer of the soil. Does the pit feelwarm inside?Paheli asked, “There are so manytrees here. Also, there are many forestlike this. What difference will it make ifwe cut some trees for a factory?”Prof Ahmad said, “You have readabout autotrophs, heterotrophs andsaprotrophs. You have learnt how greenplants produce food. All animals,whether herbivores or carnivores,depend ultimately on plants for food.Organisms which feed on plants oftenget eaten by other organisms, and soon. For example, grass is eaten byinsects, which in turn, is taken by thefrog. The frog is consumed by snakes.This is said to form a food chain:Grass → insects → frog → snake → eagle.Many food chains can be found in theforest. All food chains are linked. If anyone food chain is disturbed, it affectsother food chains. Every part of theforest is dependent on the other parts.If we remove one component, say trees,all other components would be affected.”Prof Ahmad asked children to pickup leaves from the forest floor andobserve them under a hand lens. Theyfound tiny mushrooms over theOxygenCarbon dioxidePhotosynthesisNutrientsDecomposersSoilWaterFig. 17.9 Interrelationship of plant, soil and decomposers in a forest: O211FORESTSORESTS: : OURLIFELINE211

www.GOALias.blogspot.comdecaying leaves. They also saw an armyof tiny insects, millipedes, ants andbeetle on them. They were wonderinghow these organisms live there. Prof Ahmadexplained that apart from these animalswhich are easily seen, there are severalorganisms and micro-organisms thatlive in the soil. Paheli wondered whatmushroom and other micro-organismseat. Prof Ahmad replied that they feedupon the dead plant and animal tissuesand convert them into a dark colouredsubstance called humus.You have learnt about humus inChapter 9. In which layer of the soilwould you find humus? What is itsimportance to the soil?The micro-organisms which convertthe dead plants and animals to humusare known as decomposers. Thesemicro-organisms play an important rolein the forest. Soon, Paheli removed somedead leaves and discovered under thema layer of humus on forest floor. Thepresence of humus ensures that thenutrients of the dead plants andanimals are released into the soil. Fromthere, these nutrients are again absorbedby the roots of the living plants. “Whathappens if an animal dies in the forest?”Sheila asked. Tibu replied the deadanimals become food for vultures, crows,jackals and insects.” In this way, thenutrients are cycled. So, nothing goeswaste in a forest (Fig. 17.9).Paheli reminded Prof Ahmad that hehad not explained why forests are calledgreen lungs. Prof Ahmad explained thatplants release oxygen through theprocess of photosynthesis. The plantshelp to provide oxygen for animalrespiration. They also maintain thebalance of oxygen and carbon dioxidein the atmosphere (Fig. 17.10). That iswhy forests are called lungs.Paheli reminded theirfriends that they havestudied photosynthesis inChapter 1.Fig. 17.10 Balance of oxygen and carbondioxideThe children saw clouds forming inthe sky. Boojho recalled what he hadlearnt about the water cycle in Class VI.Trees take in water from their roots andrelease water vapour into the airthrough evaporation.If there were fewer trees, how will thewater cycle be affected?Tibu told them that the forest is notjust home to plants and animals. Manypeople also live in the forest. Some ofthem may belong to different tribes. Tibuexplained that these people dependmostly on the forests. The forest provides212SCIENCE

www.GOALias.blogspot.comthem with food, shelter, water andmedicines. They have traditionalknowledge about many medicinal plantsin the forest.While Boojho was drinking waterfrom a small stream, he saw some deercrossing the stream (Fig. 17.11). Theydisappeared into the bushes. The densebushes and the tall grass provideanimals with the food and shelter. Theyalso protect them from carnivores thatlive in the forest.between various types of droppings.Prof Ahmad informed them that theforest officers could recognise thepresence of some animals in the forestby their droppings and footprints.Boojho called every one and showedthem a large, decaying heap of animaldropping. Several beetles and grubswere feeding on the heap and a bunchof seedlings was sprouting. “Theseseedlings are of the herbs and shrubs.The animals also disperse the seeds ofcertain plants and help the forest to growFig. 17.11 Deer in a forestFig. 17.12 A sapling on a wallPaheli remembered that shesaw a Pipal sapling on thesidewall in her school. Can youhelp her to understand how thiswould have happened?Tibu then started looking closely atthe forest floor. Soon he called andshowed the children droppings of someanimals, and explained the differenceand regenerate. The decaying animaldung also provides nutrients to theseedlings to grow”, said Prof Ahmad.After listening to this, Boojho notedin his notebook, “By harbouring greatervariety of plants, the forest providesgreater opportunities for food andhabitat for the herbivores. Largernumber of herbivores means increasedavailability of food for a variety ofcarnivores. The wide variety of animals: O213FORESTSORESTS: : OURLIFELINE213

www.GOALias.blogspot.comRainTranspiration and evaporationThe closed canopy andmany layers of vegetationslow down the speed ofraindropsRoot systemCovered ground withdecaying material actslike a spongeThe root system helpswater to seep down inthe groundWater tableFig. 17.13 Rainwater drips from the trees and seeps into the groundhelps the forest to regenerate and grow.Decomposers help in maintaining thesupply of nutrients to the growing plantsin the forest. Therefore, the forest is a‘dynamic living entity’ — full of life andvitality.”It was about afternoon and thechildren wanted to go back. Tibu214suggested another route for going back.While they were going back, it startedraining. However, surprisingly, they sawthat the raindrops were not hitting theforest floor directly. The uppermost layerof the forest canopy intercepted the flowof raindrops, and most of the water wascoming down through the branches andSCIENCE

www.GOALias.blogspot.comthe stems of the trees. From the leavesit was dripping slowly over branches ofthe shrubs and herbs (Fig. 17.13). Theyfound that the ground was still dry. Afterabout half an hour, the rain stopped.They noticed that the layer of deadleaves over the forest floor appeared wetnow. But water did not stagnate in theforest.Boojho thought that if it had rainedso heavily in his town, it would haveflooded the drains and roads.What would happen if it rains heavilyin your town?Prof Ahmad told them that the forestalso acts as a natural absorber ofrainwater and allows it to seep. It helpsmaintain the water table throughout theyear. Forests not only help in controllingfloods but also help maintain the flowof water in the streams so that we get asteady supply of water. On the otherhand, if trees are not present, rain hitsthe ground directly and may flood thearea around it. Heavy rain may alsodamages the soil. Roots of trees normallybind the soil together, but in theirabsence the soil is washed away oreroded.The children spent an hour at Tibu’svillage on their way back. The weatherof the village was quite pleasant. Villagerstold them that due to the surroundingforest, they receive good rainfall. The airalso remained cool. Noise pollution, toois less because the forest absorbs thenoise of the nearby highway.The children learnt about the historyof the village. It surprised them that thevillages and the agricultural fields ofthat area were created after clearing theforest about sixty years ago. Tibu’sgrandfather told them that when he wasyoung, the village was not as large as itwas now. It was also surroundedby forests. Construction of roads,buildings, industrial development andincreasing demand of wood createdpressure on the forests and it startedvanishing. He was not happy that theforest adjoining their village is notregenerating and is on the verge ofdisappearing due to overgrazing ofanimals and indiscriminate felling oftrees. Prof Ahmad said that if we didthings wisely we could preserve forestsand environment as well as havedevelopment.Children prepared a few pictures toshow the consequences of such anevent.At the end of the visit, Prof Ahmadasked children to sum up theimportance of forests. The childrenwrote: Forests provide us with oxygen.They protect soil and provide habitat toa large number of animals. Forestshelp in bringing good rainfall inneighbouring areas. They are a sourceof medicinal plants, timber and manyother useful products. We must preserveour forests.What would happen if forestsdisappear?: O215FORESTSORESTS: : OURLIFELINE215

www.GOALias.blogspot.com121 If forests disappear, theamount of carbon dioxide inair will increase, resulting inthe increase of earth’stemperature.2 In the absence of trees andplants, the animals will notget food and shelter.3 In the absence of trees, thesoil will not hold water, whichwill cause floods.4 Deforestation will endangerour life and environment.Think, what we can do topreserve our forests.34216SCIENCE

www.GOALias.blogspot.comKeywordsCanopyCrownDecomposersDeforestationHumusRegenerationSeed dispersalSoil erosionUnderstoreyWhat you have learnt• We get various products from the forests surrounding us.• Forest is a system comprising various plants, animals andmicro-organisms.• In a forest, trees form the uppermost layer, followed by shrubs.The herbs form the lowest layer of vegetation.• Different layers of vegetation provide food and shelter for animals,birds and insects.• The various components of the forest are interdependent on oneanother.• The forest keeps on growing and changing, and can regenerate.• In the forest, there is interaction between soil, water, air andliving organisms.• Forests protect the soil from erosion.• Soil helps forests to grow and regenerate.• Forests are the lifeline for the forest-dwelling communities.• Forests influence climate, water cycle and air quality.Exercises1. Explain how animals dwelling in the forest help it grow and regenerate.2. Explain how forests prevent floods.3. What are decomposers? Name any two of them. What do they do in theforest?4. Explain the role of forest in maintaining the balance between oxygenand carbon dioxide in the atmosphere.5. Explain why there is no waste in a forest.6. List five products we get from forests?: O217FORESTSORESTS: : OURLIFELINE217

www.GOALias.blogspot.com7. Fill in the blank:(a)The insects, butterflies, honeybees and birds help flowering plantsin .(b) A forest is a purifier of and .(c) Herbs form the layer in the forest.(d)The decaying leaves and animal droppings in a forest enrich the.8. Why should we worry about the conditions and issues related to forestsfar from us?9. Explain why there is a need of variety of animals and plants in a forest.10. In Fig. 17.15, the artist has forgotten to put the labels and directions onthe arrows. Mark the directions on the arrows and label the diagramusing the following labels:clouds, rain, atmosphere, carbon dioxide, oxygen, plants, animals, soil,roots, water table.11. Which of the following is nota forest product?(i)(ii)GumPlywood(iii) Sealing wax(iv) Kerosene12. Which of the followingstatements is not correct?(i) Forests protect the soilfrom erosion.(ii) Plants and animals ina forest are notdepedent on oneanother.(iii)(iv)Forests influence theclimate and watercycle.Soil helps forests togrow and regenerate.Carbon dioxideOxygenFig. 17.15218SCIENCE

www.GOALias.blogspot.com13. Micro-organisms act upon the dead plants to produce(i) sand (ii) mushrooms (iii) humus (iv) woodExtended Learning — Activities and Projects1. The Department of Environment is to decide whether some portion of aforest in your area could be cleared for a housing complex. Write a letterto the department explaining your point of view as a concerned citizen.2. Visit a forest. Here is a list of points that would make your visit morefruitful.(a)(b)(c)(d)(e)Make sure that you have permission to go into the forest.Make sure that you can find your way around. Get a map and goalong with some one who is familiar with the area.Keep a record of the things you see and do. Observations makethe visit interesting. Sketches and photographs are useful.You may record bird calls.Collect different kinds of seeds or hard fruits like nuts.( f ) Try to recognise various types of trees, shrubs, herbs, etc. Makelists of plants from different places in the forest and of differentlayers. You may not be able to name all the plants, but it is worthrecording and seeing where they grow. Make a record ofapproximate heights of plants, crown shape, bark texture, leafsize, and flower colour.(g)(h)Learn to recognise the animal’s droppings.Interview the forest officials and the people of surrounding villages and other visitors.You must never collect birds’ eggs, and their nests should never bedisturbed.You can read more on the following website:www.wild-india.comDid you know?In India the area under forest cover is about 21% of the total area. It hadsteadily been falling since independence. But people now seem to haverealised the importance of the forest cover. Reports suggest that the areaunder forest cover has slightly increased in recent years.: O219FORESTSORESTS: : OURLIFELINE219

www.GOALias.blogspot.com1818 Wastewater StoryAll of us use water in our homes andmake it dirty.Dirty! Are you surprised?Rich in lather, mixed with oil, black–brown water that goes down the drainsfrom sinks, showers, toilets, laundriesis dirty. It is called wastewater. Thisused water should not be wasted. Wemust clean it up by removing pollutants.Have you ever thought where thewastewater goes and what happens to it?18.1 WATERATER, , OURLIFELINEClean water is a basic need of humanbeing. Let us make a mindmap of themany uses of clean water.Activity 18.1(We have given one example of theuse of clean water. You can add manymore.)Clean waterput to useDrinkingClean water that is fitfor use is unfortunatelynot available to all. Ithas been reported thatmore than one billion ofour fellow human beingshave no access to safe drinking water.This accounts for a large number ofwater-related diseases and even deaths.Women and girls walk for severalkilometres to collect clean water, as youread in Chapter 16. Is it not a seriousmatter for human dignity?You have studied in Chapter 16about the increasing scarcity of freshwaterdue to population growth,pollution, industrial development,mismanagement and other factors.Realising the urgency of the situationon the World Water Day, on 22 March2005, the General Assembly of theUnited Nations proclaimed the period2005–2015 as the International Decadefor action on “Water for life”. All effortsmade during this decade aim to reduceby half the number of people who donot have access to safe drinking water.Cleaning of water is a process ofremoving pollutants before it enters awater body or is reused. This process ofwastewater treatment is commonlyknown as “Sewage Treatment”. It takesplace in several stages.220SCIENCE

www.GOALias.blogspot.com18.2 W18.2 WHATIS SEWAGEEWAGE?Sewage is wastewater released by homes,industries, hospitals, offices and otherusers. It also includes rainwater that hasrun down the street during a storm orheavy rain. The water that washes offroads and rooftops carries harmfulsubstances with it. Sewage is a liquid waste.Most of it is water, which has dissolvedand suspended impurities. Theseimpurities are called contaminants.Activity 18.2Locate an open drain near your home,school or on the roadside and inspectwater flowing through it.Record colour, odour and any otherobservation. Discuss with your friendsand your teacher and fill up thefollowing Table 18.1.We know that sewage is a complexmixture containing suspended solids,organic and inorganic impurities,nutrients, saprotrophic and diseasecausing bacteria and other microbes.Organic impurities –Human faeces,animal waste,oil, urea (urine),Table 18.1 Contaminant surveypesticides,herbicides, fruitand vegetablewaste, etc.Inorganic impurities – Nitrates,Phosphates,metals.Nutrients– Phosphorusand Nitrogen.Bacteria– Such as whichcause choleraand typhoid.Other microbes – Such as whichcause dysentery.18.3 WATERFRESHENSUP — ANEVENTFULJOURNEYIn a home or a public building generallyone set of pipes brings clean water andanother set of pipes takes awaywastewater. Imagine that we could seethrough the ground. We would see anetwork of big and small pipes, calledsewers, forming the sewerage. It is likea transport system that carries sewagefrom the point of being produced to thepoint of disposal, i.e. treatment plant.Manholes are located at every 50 mto 60 m in the sewerage, at the junctionS. No. Type of sewagePoint of originSubstances whichcontaminateAny otherremark1. Sullage water Kitchen2. Foul waste Toilets3. Trade waste Industrialand commercialorganisations221WASTEWATERSTORY221

www.GOALias.blogspot.comof two or more sewers and at pointswhere there is a change in direction.Activity 18.3Study the sewage route in your home/school/building. Do the following:• Make a line diagram of the sewageroute.• Walk down the street or survey thecampus to find the number ofmanholes.• Follow an open drain and find outwhere it ends and which livingorganisms are found in andaround it.In case you do not have a seweragesystem in your locality, find out howsewage is being disposed off.Treatment of polluted waterPerform the following activity. It will helpyou understand the processes that takeplace at the wastewater treatment plant.Activity 18.4Divide yourself into groups to performthe activity. Record observations at eachstage:• Fill a large glass jar 3/4 full of water.Add some dirty organic matter suchas grass pieces or orange peels, asmall amount of detergent, and a fewdrops of an ink or any colour.• Cap the jar, shake it well and let themixture stand in the sun for twodays.• After two days, shake the mixtureand pour a small sample into testtube. Label this test tube “Beforetreatment; Sample 1”. How does itsmell?• Use an aerator from an aquarium tobubble air through the sample in theglass jar. Allow several hours foraeration; leave the aerator attachedovernight. If you do not have anaerator, use a mechanical stirrer ora mixer. You may have to stir itseveral times.• The next day when aeration iscomplete, pour another sample intoa second test tube. Label it as “Afteraeration; Sample 2”.• Fold a piece of filter paper to form acone. Wet the paper with tap waterand then insert the cone in a funnel.Mount the funnel on a support(as you have learnt in Class VI).• Place layers of sand, fine gravel andfinally medium gravel in the funnel(Fig. 18.2). (An actual filtration plantdoes not use filter paper, but the sandfilter is several metres deep).• Pour the remaining aerated liquidthrough the filter into the beakers.Do not allow the liquid to spill overthe filter. If the filtered liquid is notclear, filter it a few times till you getclear water.• Pour a sample of the filtered waterinto a third test tube labelled“Filtered; Sample 3”.• Pour another sample of the filteredwater into a fourth test tube. Add asmall piece of a chlorine tablet. Mixwell until the water is clear. Label thetest tube “Chlorinated; Sample 4”.222SCIENCE

www.GOALias.blogspot.comFig. 18.2 Filtration process Fig. 18.3 Bar screen• Observe carefully the samples in allthe test tubes. Do not taste! Justsmell them!Now answer the following questions:(a) What changes did you observe in theappearance of the liquid afteraeration?(b) Did aeration change the odour?(c) What was removed by the sand filter?(d) Did chlorine remove the colour?(e) Did chlorine have an odour? Was itworse than that of the wastewater?18.4 WASTEWATERTREATMENTPLANT(WWTP)Treatment of wastewater involvesphysical, chemical, and biologicalprocesses, which remove physical,chemical and biological matter thatcontaminates the wastewater.1. Wastewater is passed through barscreens. Large objects like rags,sticks, cans, plastic packets, napkinsare removed (Fig. 18.3).2. Water then goes to a grit and sandremoval tank. The speed of theincoming wastewater is decreased toallow sand, grit and pebbles to settledown (Fig. 18.4).Fig. 18.4 Grit and sand removal tank3. The water is then allowed to settle ina large tank which is sloped towardsthe middle. Solids like faeces settleat the bottom and are removed witha scraper. This is the sludge. Askimmer removes the floatable solidslike oil and grease. Water so clearedis called clarified water (Fig. 18.5).223WASTEWATERSTORY223

www.GOALias.blogspot.comFig. 18.5 Water clariferThe sludge is transferred to aseparate tank where it is decomposedby the anaerobic bacteria. The biogasproduced in the process can be used asfuel or can be used to produce electricity.4. Air is pumped into the clarified waterto help aerobic bacteria to grow.Bacteria consume human waste,food waste, soaps and otherunwanted matter still remaining inclarified water (Fig. 18.6).After several hours, the suspendedmicrobes settle at the bottom of the tankas activated sludge. The water is thenremoved from the top.The activated sludge is about 97%water. The water is removed by sanddrying beds or machines. Dried sludgeis used as manure, returning organicmatter and nutrients to the soil.The treated water has a very low levelof organic material and suspendedmatter. It is discharged into a sea, a riveror into the ground. Nature cleans it upfurther. Sometimes it may be necessaryto disinfect water with chemicals likechlorine and ozone before releasing itinto the distribution system.Become an active citizenWaste generation is a natural part ofhuman activity. But we can limit thetype of waste and quantity of wasteproduced. Often we have been repelledby offensive smell. The sight of opendrains is disgusting. The situationThe water in a river is cleanednaturally by processes that aresimilar to those adopted in awastewater treatment plant.Did you know ?Fig. 18.6 AeratorIt has been suggested that we shouldplant eucalyptus trees all alongsewage ponds. These trees absorb allsurplus wastewater rapidly andrelease pure water vapour into theatmosphere.224SCIENCE

www.GOALias.blogspot.comworsens in the rainy season when thedrains start overflowing. We have towade through the mud pools on theroads. Most unhygienic and unsanitaryconditions prevail. Flies, mosquitoes andother insects breed in it.You can be an enlightened citizenand approach the municipality or thegram panchayat. Insist that the opendrains be covered. If the sewage ofany particular house makes theneighbourhood dirty, you should• Used tealeaves, solid food remains,soft toys, cotton, sanitary towels, etc.should also be thrown in the dustbin(Fig. 18.7). These wastes choke theDon’t add to the load ofWWTP. Paheli wonders how!request them to be more considerateabout others’ health.18.618.6 BETTERHOUSEKEEPINGPRACTICESOne of the ways to minimise or eliminatewaste and pollutants at their source isto see what you are releasing down thedrain.• Cooking oil and fats should not bethrown down the drain. They canharden and block the pipes. In anopen drain the fats clog the soil poresreducing its effectiveness in filteringwater. Throw oil and fats in thedustbin.• Chemicals like paints, solvents,insecticides, motor oil, medicinesmay kill microbes that help purifywater. So do not throw them downthe drain.Fig. 18.7 Do not throw every thing in the sinkdrains. They do not allow free flowof oxygen. This hampers thedegradation process.18.7 SANITATIONAND DISEASEPoor sanitation and contaminateddrinking water is the cause of a largenumber of diseases.Let us look at our own country. Avast number of our people are still225WASTEWATERSTORY225

www.GOALias.blogspot.comVermi-processing toiletA design of a toilet in which humans excreta is treated by earthworms has beentested in India. It has been found to be a novel, low water-use toilet for safeprocessing of human waste. The operation of the toilet is very simple and hygienic.The human excreta is completely converted to vermi cakes — a resource muchneeded for soil.without sewerage facilities. Where dothey relieve themselves?A very large fraction of our peopledefecates in the open, on dry riverbeds,on railway tracks, near fields and manya time directly in water. Untreatedhuman excreta is a health hazard. Itmay cause water pollution and soilpollution. Both the surface water andgroundwater get polluted. Groundwateris a source of water for wells, tubewells,springs and many rivers as you learntin Chapter 16. Thus, it becomes themost common route for water bornediseases. They include cholera, typhoid,polio, meningitis, hepatitis anddysentery.18.8 ALTERNATIVEARRANGEMENTFORSEWAGEDISPOSALTo improve sanitation, low cost onsitesewage disposal systems are beingencouraged. Examples are septic tanks,chemical toilets, composting pits. Septictanks are suitable for places where thereis no sewerage system, for hospitals,Bhoojo wants to know howsewage is disposed of in anaeroplane.isolated buildings or a cluster of 4 to 5houses.Some organisations offer hygienicon-site human waste disposaltechnology. These toilets do not requirescavenging. Excreta from the toilet seatsflow through covered drains into abiogas plant. The biogas produced isused as a source of energy.18.9 SANITATIONAT PUBLICPLACESIn our country fairs are organisedperiodically. A large number of peopleparticipate in them. In the same wayrailway stations, bus depots, airports,hospitals are very busy places.Thousands of people visit them daily.Large amount of waste is generatedhere. It must be disposed of properlyotherwise epidemics could break out.The government has laid downcertain standards of sanitation but,unfortunately, they are not strictlyenforced.However, all of us can contribute inmaintaining sanitation at public places.We should not scatter litter anywhere.If there is no dustbin in sight, we shouldcarry the litter home and throw it in thedustbin.226SCIENCE

www.GOALias.blogspot.comConclusionWe all have a role to play in keeping ourenvironment clean and healthy. Youmust realise your responsibility inmaintaining the water sources in ahealthy state. Adopting good sanitationpractices should be our way of life. Asan agent of change your individualinitiative will make a great difference.Influence others with your energy, ideasand optimism. A lot can be done if peoplework together. There is great power incollective action.Mahatma Gandhi said:“No one need to wait for anyone elseto adopt a humane and enlightenedcourse of action.”KeywordsAerationAerobic bacteriaAnaerobic bacteriaBiogasContaminantSanitationSewageSewerSewerageSludgeWastewaterWhat you have learnt• Used water is wastewater. Wastewater could be reused.• Wastewater is generated in homes, industries, agricultural fields and inother human activities. This is called sewage.• Sewage is a liquid waste which causes water and soil pollution.• Wastewater is treated in a sewage treatment plant.• Treatment plants reduce pollutants in wastewater to a level where naturecan take care of it.• Where underground sewerage systems and refuse disposal systems arenot available, the low cost on-site sanitation system can be adopted.• By-products of wastewater treatment are sludge and biogas.• Open drain system is a breeding place for flies, mosquitoes and organismswhich cause diseases.• We should not defecate in the open. It is possible to have safe disposal ofexcreta by low cost methods.227WASTEWATERSTORY227

www.GOALias.blogspot.comExercises1. Fill in the blanks:(a) Cleaning of water is a process of removing ____________.(b) Wastewater released by houses is called ____________.(c) Dried ____________ is used as manure.(d) Drains get blocked by ____________ and ____________.2. What is sewage? Explain why it is harmful to discharge untreatedsewage into rivers or seas.3. Why should oils and fats be not released in the drain? Explain.4. Describe the steps involved in getting clarified water from wastewater.5. What is sludge? Explain how it is treated.6. Untreated human excreta is a health hazard. Explain.7. Name two chemicals used to disinfect water.8. Explain the function of bar screens in a wastewater treatment plant.9. Explain the relationship between sanitation and disease.10. Outline your role as an active citizen in relation to sanitation.11. Here is a crossword puzzle: Good luck!228SCIENCE

www.GOALias.blogspot.comAcross3. Liquid waste products4. Solid waste extracted in sewage treatment6. A word related to hygiene8. Waste matter discharged from human bodyDown1. Used water2. A pipe carrying sewage5. Micro-organisms which causes cholera7. A chemical to disinfect water12. Study the following statements about ozone:(a) It is essential for breathing of living organisms.(b) It is used to disinfect water.(c) It absorbs ultraviolet rays.(d) Its proportion in air is about 3%.Which of these statements are correct?(i) (a), (b) and (c)(ii) (b) and (c)(iii) (a) and (d)(iv) All fourExtended Learning — Activities and Projects1. Construct a crossword puzzle of your own using the keywords.2. Then and now: Talk to your grand parents and other elderly people inthe neighbourhood. Find out the sewage disposal systems available tothem. You can also write letters to people living in far off places to getmore information. Prepare a brief report on the information youcollected.3. Visit a sewage treatment plant.It could be as exciting and enriching as a visit to a zoo, a museum, or apark. To guide your observation here are a few suggestions.Record in your notepad:Place ___________ Date ___________ Time ___________Name of the official at the plant __________ Guide/Teacher ___________229WASTEWATERSTORY229

www.GOALias.blogspot.com(a) The location of the sewage plant.(b) Treatment capacity.(c) The purpose of screening as the initial process.(d) How is air bubbled through the aeration tank?(e) How safe is the water at the end of the treatment? How is it tested?(f ) Where is the water discharged after treatment?(g) What happens to the plant during heavy rains?(h) Is biogas consumed within the plant or sold to other consumers?(i) What happens to the treated sludge?( j) Is there any special effort to protect nearby houses from the plant?(k) Other observations.For more information, consult:Millennium Development Goals:http://www.un.org/millenniumgoals/“Water for Life” International Decade for Action:http://www.un.org/waterforlifedecade/World Water Day - Themes and Importance:http://www.worldwaterday.org/Through the ages Development of Sanitation:http://www.sewerhistory.org/http://www.cep.unep.org/pubs/Techreports/tr43en/Household%20systems.htm“By providing clean water and sanitation to the poorest people on theplanet, we can reduce poverty and suffering and ensure education for allchildren.” — UNICEFAn early engineering feat: Indus valley civilisationOne of the ancient civilisations, Harappa and Mohenjodaro had perhapsthe world’s first urban sanitation system. Within the city individualhouses, or groups of houses, obtained water from wells. There was aseparate room for bathing, and wastewater was directed to the covereddrains which lined the major streets. The oldest toilet made of bricks isabout 4500 years old.230SCIENCE

C KC Kwww.GOALias.blogspot.comINDEXAAbsorption 17Acid 49Acidic 49Adaptation 72Aeration 222Aerobic bacteria 224Aerobic respiration 108Amino acid 17Ammonia 127Amoeba 18Anaerobic bacteria 224Anaerobic respiration 108Anemometer 90Aquifer 197Artery 121,122Asexual reproduction 133Assimilation 17Autotrophic 1BBar graph 151Base 49Basic 49Battery 161Bile 16Biogas 226Blood vessels 121,122Blood 121Breathing rate 110Buccal cavity 12Budding 135CCanine 13Canopy 209Capillary 123Cellular respiration 108Cellulose 18Celsius scale 36Chemical change 59Chemical reaction 62Chlorophyll 2Circuit diagram 163Circulatory system 121Clayey 99Climate 71Cocoon 28,29Concave lens 183Concave mirror 179,180,181,182Conduction 40Conductor 41Contaminant 221Convection 42Convex lens 183Convex mirror 179,183Crown 209Crystallisation 64Cyclone 86,87DDecomposers 212Depletion 198Dialysis 127Diaphragm 111Digestion 11Drip irrigation 201EEgestion 17Electric bell 168Electric components 160Electromagnet 168Elements of weather 69Embryo 138Erect image 177Excretion 126Excretory system 126Exhalation 110FFatty acid 17Fertilisation 138

C KC Kwww.GOALias.blogspot.com232Fleece 24,26Food vacuole 18,19Fragmentation 136Fuse 166GGall bladder 16Galvanisation 64Gametes 137Gills 116Glycerol 17Graphs 151Groundwater 197HHaemoglobin 122Heartbeat 125Heating effect 163,164Heterotrophs 1Host 5Humidity 69Humus 97,212Hurricane 89Hypha 136IIncisor 13Indicator 49Infiltration 197Ingestion 13Inhalation 109Insectivorous 5Insulator 41KKidneys 126LLand breeze 42Lightning 87Liver 12Loamy 99Low pressure 83MMagnetic effect 167Magnified image 185Magnifying glass 183Maximum temperature 70Migration 74Milk teeth 13Minimum temperature 70Moisture 101Molar 13Monsoon winds 85NNeutral 51Neutralisation 54,55Nonuniform motion 145Nutrient 1Nutrition 1OOesophagus 12,15Oscillation 146Ovule 137PPancreas 12Parasite 5Percolation 100Permanent teeth 13Phloem 129Photosynthesis 2Physical change 58,59Plasma 122Platelets 122Polar region 72,73Pollen grain 138Pollen tube 138Pollination 137,138Premolar 13Pressure 81Prism 186Pseudopodia 18Pulse 122

C KC Kwww.GOALias.blogspot.com233RRadiation 43Rainbow 186Real image 180Rear view mirror 178Recharge 201Red blood cell 122Reeling 31Regeneration 213Root hair 128Rumen 18Ruminant 18Rumination 18Rusting 59SSaliva 14Salivary glands 12Salt 55Sandy 99Sanitation 225Saprotrophs 6Saprotrophic 6Scouring 27Sea breeze 42Seed dispersal 138,213Sericulture 28Sewage 221Sewer 221Sexual reproduction 133,136Shearing 26Side mirror 183Silk moth 28,29Silkworm 28Simple pendulum 145,146Sludge 223Soil erosion 215Sorting 27Speed 144Spherical mirror 179Spiracles 115Sporangium 136Spore 136Stethoscope 125Stomata 2Sweat 127TTemperature 36Thermometer 36Thunderstorms 86,87Time period 146Tissue 129Tornado 89,90Trachea 115Tropical rainforest 75Tropical region 75Typhoon 89UUnderstorey 209Uniform motion 145Unit of time 147Urea 127Ureter 127Urethra 127Uric acid 127Urinary bladder 127VVegetative propagation 133Vein 122,123Villi 17Virtual image 180WWastewater 220Water harvesting 201Water retention 102Water table 197Weather 68,69White blood cell 122Wind flow pattern 85XXylem 129ZZygote 138

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