com www.GOALias.blogspot.com www.GOALias ... - fun learning

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