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Food Chains and Energy Flow
Concepts tested here
- Trophic levels and ten percent law
All Questions
2008 AIPMT 1 question
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Consider the following statements concerning food chains:
(i) Removal of 80% tigers from an area resulted in greatly increased growth of vegetation
(ii) Removal of most of the carnivores resulted in an increased population of deers
(iii) The length of food chains is generally limited to 3-4 trophic levels due to energy loss
(iv) The length of food chains may vary from 2 to 8 trophic levels
Which two of the above statements are correct?(ii) is correct: carnivores keep the population of herbivores in check. When most of the carnivores are removed, predation pressure falls and the population of deer increases.
(iii) is correct: according to the 10 percent law, only about 10 percent of the energy is transferred from one trophic level to the next; the rest is lost as heat in respiration. So very little energy is left after 3 to 4 transfers, and the number of trophic levels in a food chain is restricted to 3-4.
(i) is not correct: removal of tigers increases the number of herbivores, which graze more, so the vegetation decreases instead of increasing.
(iv) is not correct: food chains do not extend to 8 trophic levels, because the energy available becomes too small to support them.
So the two correct statements are (ii) and (iii).