Science — CBSE Class 10 board question

Pesticides and chemical fertilizers used in paddy fields are washed into the soil and nearby waterbodies. Small aquatic plants and animals absorb these chemicals. When small fish eat these plants/organisms, the chemicals enter their bodies. Larger fish then eat the smaller fish, and humans consume these larger fish.

At each step of the food chain, these chemicals are not broken down and keep accumulating in increasing concentrations. By the time they reach humans (at the top of the food chain), the concentration becomes very high and harmful.

This phenomenon of gradual increase in concentration of harmful chemicals at each successive trophic level of a food chain is called Biological Magnification (or Biomagnification).

Source: Our Environment, Chapter 13

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• The examiner expects two parts: (1) the pathway — how chemicals travel through the food chain, and (2) the name of the phenomenon — biological magnification.
• Always mention that concentration increases at each trophic level and is highest in humans (top consumers).
• This is a 3-mark question; cover the food chain route briefly and name the phenomenon clearly. Naming it alone without explanation won't fetch full marks.