Q. 625.0( 2 Votes )

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?

Answer :

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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