Assertion : Heavy metals and persistent pesistent 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.

Answer

C

Explanation

Heavy metals and persisten pesticides (e.g., organochlorine 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 metabloised 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 metabloism in birds, which causes thinning of egge shell and their premature breaking, eventually causing decline in bird population. These chlorinated hydrocarbons affect CNS, cause softening of brain, cerebral haemorrhage, liver cirrhosis, hypertensin and also affect an organism's reproductive system.