CBSE Class 10 Science 2020 · Paper 31/3/3 · Question 18(a)
- (a)State with reason the consequence of decrease in number of carnivores in an ecosystem.
- (b)In a food chain, state the trophic level at which the concentration of harmful chemicals is maximum. Why is it so ?
Answer
Fewer carnivores let herbivores increase and over-graze plants; harmful chemicals are highest in top carnivores because they accumulate at each level (biological magnification).
(a) The population of herbivores will increase, because the carnivores that prey on them are fewer, so fewer herbivores are eaten. The extra herbivores then over-graze the plants, so the vegetation decreases and the balance of the ecosystem is disturbed.
(b) At the highest trophic level, the top carnivores (tertiary consumers). Harmful chemicals such as pesticides are non-biodegradable, so they are not broken down; as they pass from one trophic level to the next they accumulate progressively at each level and reach their maximum concentration at the top. This is biological magnification.
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