Explain how the use of pesticides on farmland can lead to a decrease in the population of birds of prey in the area.

WJEC GCSE Biology (Wales) — 1.6.3 Human impact on the environment · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Pesticides are sprayed onto crops to kill pest insects and invertebrates.
The chemicals accumulate in the bodies of the insects that absorb them (bio‑accumulation).
Small animals that feed on these insects, such as small birds and mice, then have higher concentrations of pesticide in their tissues.
Birds of prey, which eat many of these contaminated animals, accumulate toxic levels of pesticide, leading to death or reduced reproduction and a decline in their population.

Examiner tips

  • Use the word ‘accumulate’ to show bio‑accumulation. Show the chain of transfer from crops to insects to prey to birds of prey. Mention the effects on birds (death, reduced reproduction).

Common mistakes

  • Confusing bio‑accumulation with bio‑concentration. Forgetting to link the pesticide to the prey animals. Using vague terms like ‘harm’ instead of specific effects such as ‘death’ or ‘reduced reproduction’.

Mark scheme (4 marks)

  1. Pesticides are sprayed onto crops / used to kill pest insects / invertebrates on farmland
  2. The pesticide accumulates / builds up in the body tissues of the insects / small organisms that absorb it (bioaccumulation)
  3. Animals that eat large numbers of the contaminated insects / prey (e.g. small birds, mice) accumulate higher concentrations of pesticide in their tissues
  4. Birds of prey eat many contaminated prey animals so accumulate toxic / lethal concentrations of pesticide, causing death / reduced reproduction / population decline

Key terms in this question

pesticide · birds of prey

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