UPSC Prelims 2010 · General Studies
Question 23: Environment and Ecology
A pesticide which is a chlorinated hydrocarbon is sprayed on a food crop. The food chain is : Food crop – Rat – Snake – Hawk. In this food chain, the highest concentration of the pesticide would accumulate in which one of the following ?
AnswerThe answer is (d).
Chlorinated hydrocarbon pesticides such as DDT do not break down easily and are stored in body fat. At each step up a food chain an animal eats many of the one below, so the stored pesticide builds up (biomagnification). In the chain food crop, rat, snake, hawk, the hawk is the top carnivore and therefore carries the highest concentration. This is why birds of prey were hit hardest by DDT. Remember: persistent, fat-soluble poisons magnify up the food chain; the top consumer carries the most.
Why each option is right or wrong
- (a) The crop has only the sprayed residue; concentration rises up the chain.
- (b) The rat has more than the crop but less than its predators.
- (c) The snake holds more than the rat but less than the hawk.
- (d) Right: the top predator accumulates the most through biomagnification.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2010, General Studies, Series A. The paper on upsc.gov.in.