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Question

Assertion :Heavy metals and persistent pesticides pass into the food chain and increase in amount per unit weight of the organism at successive trophic levels Reason: Heavy metals and persistent pesticides can be easily metabolised by the organism's body.

A
Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
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B
Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
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C
Assertion is correct but Reason is incorrect
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D
Both Assertion and Reason are incorrect
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Solution

The correct option is C Assertion is correct but Reason is incorrect
Heavy metals and persistent pesticides (e.g., organo-chlorine or chlorinated hydrocarbons like DDT) pass into food chain and increase in amount per unit weight of organisms with the rise in trophic level due to their accumulation in fat. The phenomenon is called biomagnification/bioconcentration/biological amplification. In other words, biomagnification refers to increase in concentration of the toxicant at successive trophic levels. This happens because a toxic substance accumulated by an organism cannot be metabolised or excreted, and is thus passed on to the next higher trophic level. this phenomenon is well-known for mercury and DDT. High concentration of DDT disturb calcium metabolism in birds, which causes thinning of egg shell and their premature breaking, eventually causing decline in bird population. These chlorinated hydrocarbons affect CNS, cause softening of brain, cerebral haemorrhage, liver cirrhosis, hypertension and also affect an organism's reproductive system.
So, the correct answer is 'Assertion is correct but Reason is incorrect'.

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