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?

Answer: (d) Hawk

The hawk is at the top. It eats many snakes, each loaded from many rats. The pesticide is fat-soluble and is excreted very slowly, so it builds up at every step.

The idea

Two different words. Bioaccumulation means poison piles up inside ONE organism over its life. Biomagnification means the concentration rises at each step UP the food chain.

Sprayed crop → Rat → Snake → Hawk = highest dose

Why the others are wrong

(a) The crop gets the spray, but its concentration is the lowest. The chain starts here.

(b) A rat eats many plants, so it holds more than the crop, but it is only the second step.

(c) A snake eats many rats, so it holds more still, but not the most.

The trap

The crop was sprayed, so it feels like it should hold the most. Concentration follows the food chain, not the spray.

Also know

DDT thinned the eggshells of eagles, ospreys and peregrine falcons, and the birds crushed their own eggs while nesting (Rachel Carson, Silent Spring, 1962). DDT is a persistent organic pollutant under the Stockholm Convention (2001). India still makes it for malaria-mosquito control, which the convention allows.