# A pond ecosystem contains the following organisms: phytoplankton, water fleas, small fish, and pike. State the trophic level of each organism and describe what would happen to the population of small fish if pike were completely removed from the pond by over-harvesting.

> Cambridge International IGCSE Biology (0610) — 19.2 Food chains and food webs · Describe · 4 marks

## Mark scheme (4 marks)

1. Phytoplankton are producers / at trophic level one
2. Water fleas are primary consumers / trophic level two; small fish are secondary consumers / trophic level three; pike are tertiary consumers / trophic level four
3. The population of small fish would increase (after pike are removed)
4. Because pike are no longer predating / eating the small fish, so fewer small fish are killed / there is less predation pressure on small fish

## Key terms

- [trophic level](https://www.gradenine.co.uk/glossary/trophic-level)
- [over-harvesting](https://www.gradenine.co.uk/glossary/over-harvesting)

## Related

- [Revision notes for Cambridge International IGCSE Biology (0610)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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/a-pond-ecosystem-contains-the-following-b622066e) · Published by Druglandscape Ltd.