(a) Explain why, a food chain usually cannot have more than three or four steps.
(b) Calculate the amount of energy that will be available to big fish in the following food chain, if 10,000 J of energy is available to small algae from the sun:
Small algae → Zooplankton → Fish → Big fish
(a) Food chain generally consists of three or four steps because after that the energy available for the next organism will be so small that it will be insufficient to sustain the life of that organism.
(b) (i) Small algae can trap only 1% of the sun’s energy falling on them. 1% of 10,000 J is 100 J, so the small algae have 100 J of energy available.
(ii) Small algae are eaten up by zooplankton. According to the 10% law, 10% of 100 J is 10 J of energy which is available in zooplankton.
(iii) The zooplankton will transfer 10% of its 10 J energy to the fish. Thus, the food energy available to the fish will be 10% of 10 J, which is 1 J.
(iv) 10% of 1 J will be transferred to big fish which will be 0.1 J.
The above result can be clearly shown as: