Q62 of 163 Page 243

The surface of water in a lake appears green due to a layer of tiny free-floating organisms X on its surface. The lake water also contains organisms like water beetle, fish and tadpole. The sun shines over the lake water and provides energy for the functioning of this lake ecosystem.

(a) What could organisms X be?


(b) Write a food chain comprising of all the four organisms mentioned.


(c) What is the general name of the food chains like the one written above?


(d) Name


(i) Secondary consumer


(ii) Producer


(iii) Tertiary consumer, and


(iv) Primary consumer in the above food chain


(e) If the tertiary consumer gets 0.2 J of energy from the secondary consumer, then how much energy was radiated by the sun to the producer?

a) Phytoplankton- Algae are tiny free floating organisms on surface of water.


b) Food chain= Algae- tadpole- water beetle- fishes.


c) Aquatic food chain is the name given to the above food chain because this food chain exists in aquatic bodies where algae are producers, tadpoles are primary consumers, water beetles are secondary consumers and fishes are tertiary consumers.


d) i) Water beetles- secondary consumer


ii) Algae-producers


iii) Fishes- tertiary consumer


iv) Tadpole- primary consumer


e) If the tertiary consumer gets 0.2J of energy from the secondary consumer, then the producer would have received 20000J of energy from the sun. This is because of the 10% energy law. Producer receives 20,000J energy from sun and uses 1% of it to make food. 200J of energy is available at the producer. 10% of 200J is transferred to primary consumer which is 20J. Secondary consumer will obtain 10% of 20J=2J. The tertiary consumer will at last receive 10% of 2J which is equal to 0.2J. Thus, 20,000J energy was radiated from sun to producer.


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60

Which of the following cannot be added in a composting pit to prepare compost?

61

The gas A is used by most of the animals to obtain energy from food by the process of respiration. When A is acted upon by radiation X, it gets converted into another gas B which is an allotrope of A but poisonous when inhaled. B forms a kind of layer C in the upper atmosphere which absorbs radiations X coming from a source Y and prevents them from reaching the earth. Some chemicals Z released from the various devices on the earth are destroying the layer C slowly. In fact, a hole has already been formed in layer Cover the area D of the earth.

(a) What are gases?


(i) A, and


(ii) B? Write their molecular formulae.


(b) Name the layer C.


(c) What are (i) X, (ii) Y, and (iii) Z?


(d) Name the area D.


(e) Name any two human ailments which may be caused by X.

63

A forest ecosystem having a lot of green plants has some foxes, lions and rabbits in it.

(a) Write a food chain comprising all the four organisms mentioned above.


(b) Name


(i) one herbivore, and


(ii) two carnivores, in this food chain.


(c) Name the link which is a predator as well as a prey.


(d) Name


(i) second trophic level, and


(ii) third trophic level.


(e) Which link of this food chain can feed on second trophic level as well as third trophic level, independently?


(f) If the sun provides 1000 J of energy to the plants, then how much energy will be transferred to fox through the food chain.

64

A food chain consists of fish, larvae, phytoplankton and birds. The level of pesticides in water in which the fish, larvae and phytoplankton live is quite high.

(a) In which organisms the pesticides enter from the polluted water? What is this level of organisms known as?


(b) Which organism will have the maximum amount of pesticides accumulated through the food chain? What is this process known as?


(c) Write the food chain comprising all the organisms mentioned above.


(d) Which other organism you could write in place of bird in the above food chain?