Explain how the use of pesticides by farmers can have harmful effects on organisms that are not pests.

WJEC A-Level Biology (Wales) — 3.6 Human impact on the environment · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Farmers use pesticides to kill insects and other organisms that damage their crops. However, scientists have found that pesticides can also harm other organisms living in and around farmland.

Model answer (5 marks)

Pesticides are sprayed onto crops and can be absorbed by or remain on plants, soil and water.
Non‑target organisms such as bees, birds and hedgehogs eat or come into contact with the pesticide.
The pesticide can accumulate in the bodies of these organisms (bioaccumulation).
Organisms higher up the food chain then receive higher concentrations of pesticide (biomagnification).
This can kill or reduce the reproductive success of non‑target organisms, thereby reducing biodiversity and population numbers.

Examiner tips

Use the exact terms: bioaccumulation, biomagnification, non‑target organisms.
Show the chain from application to impact on biodiversity.
Keep each point short and clear to hit all 5 marks.

Common mistakes

Confusing bioaccumulation with biomagnification.
Lacking mention of non‑target organisms.
Using vague phrases like ‘harm to wildlife’ instead of specific mechanisms.

Mark scheme (5 marks)

Pesticides are sprayed onto crops and can be absorbed by or remain on plants/soil/water
Non-target organisms (e.g. bees / birds / hedgehogs) eat or come into contact with the pesticide
Pesticide accumulates / builds up in the body of organisms (bioaccumulation)
Organisms higher up the food chain receive higher concentrations of pesticide (biomagnification)
This can kill or reduce the reproductive success of non-target organisms, reducing biodiversity / population numbers

Key terms in this question

pesticides