Biological magnification

The idea

Non-degradable chemicals such as pesticides enter the food chain from soil and water and accumulate progressively at each trophic level, so the highest concentration builds up at the top level; this is biological magnification.

Spraying a crop

A farmer sprays a pesticide to protect a crop from pests. Rain washes some of it into the soil and water bodies.

Which organism in a food chain ends up with the highest concentration of the chemical?

• The one at the top of the chain
• The plant at the start
• The same amount in each

Follow the chemical

Press Next step.

Building up

Pesticides are not degradable, so they are not broken down. They gather in the bodies of the organisms at each trophic level. Human beings occupy the top level in any food chain, so the maximum concentration of these chemicals gets accumulated in our bodies. This is why even food grains, vegetables, fruits and meat contain varying amounts of pesticide residues.

Non-degradable chemicals such as pesticides enter the food chain from soil and water and accumulate progressively at each trophic level, so the highest concentration builds up at the top level; this is biological magnification.

Notes

Biological magnification: non-degradable chemicals build up at each level, the most at the top.

Check yourself

Why do pesticide chemicals get accumulated at each trophic level?

At which trophic level is the concentration of these chemicals the highest?

What is the build-up of such chemicals along the food chain called?

Which is one way pesticides enter a food chain?

• They are quickly broken down in the soil. Because these chemicals are not degradable, they get accumulated instead of being broken down.
• They are not degradable, so they are not broken down — correct. Yes!
• They are used up by the Sun. The chemicals enter the food chain from soil and water and stay in the bodies of organisms.
• The producers. The producers are at the first level, where the chemicals first enter. The concentration builds up as we go up.
• The second level. The concentration goes on building up at each trophic level, so it is higher at the top.
• The top level — correct. Yes!
• Biological magnification — correct. Yes!
• Photosynthesis. Photosynthesis is how producers make food.
• Decomposition. Decomposition is the breaking down of dead remains by decomposers.
• Plants make them by photosynthesis. Pesticides are chemicals used to protect crops. Plants do not make them by photosynthesis.
• They are washed into the soil and absorbed by plants with water and minerals — correct. Yes!
• Decomposers make them from dead remains. Pesticides are chemicals used to protect crops from diseases and pests. Decomposers do not make them.