# Insecticides used in farming can enter nearby rivers and accumulate in the bodies of organisms within a food chain. Explain how the use of insecticides on farmland can lead to the death of top predators living in a river ecosystem.

> Cambridge International IGCSE Biology (0610) — 20.3 Pollution · Explain · 4 marks

## Mark scheme (4 marks)

1. Insecticides are washed from fields into the river by rain / enter the waterway via run-off
2. Insecticides are taken in / absorbed by small organisms (e.g. invertebrates / insects / small fish) and are not broken down / excreted, so they accumulate in body tissues
3. Each organism at a higher trophic level consumes many organisms from the level below, so the concentration of insecticide increases at each stage of the food chain / with each trophic level
4. Top predators accumulate a lethal / toxic concentration of insecticide, causing their death

## Key terms

- [insecticides](https://www.gradenine.co.uk/glossary/insecticides)
- [food chain](https://www.gradenine.co.uk/glossary/food-chain)
- [top predator](https://www.gradenine.co.uk/glossary/top-predator)

## Related

- [Revision notes for Cambridge International IGCSE Biology (0610)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/insecticides-used-in-farming-can-enter-b934e83e) · Published by Druglandscape Ltd.