Question

(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

Answer 1

(a) At each trophic level in a food chain, a large portion of the energy available is utilised for the maintenance of organisms in that trophic level and is lost as heat. Food chains usually cannot have more than three or four steps because the energy available for organisms in any additional step will be so small that it will be insufficient to sustain the life of those organisms.

(b) The amount of energy available to big fish will be 1 J. It can be calculated as follows-

Sun $\to$ Small algae $\to$ Zooplankton $\to$ Fish $\to$ Big fish
10000 J $\to$ 1000 J $\to$ 100 J $\to$ 10 J $\to$ 1 J