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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