# A pond ecosystem contains the following organisms: microscopic algae, water fleas, small fish, and pike. Describe what is meant by a food chain and explain why the number of pike that can be supported in the pond is much smaller than the number of water fleas.

> Pearson Edexcel International GCSE Biology (4BI1) — 4.2 Feeding relationships · Describe and Explain · 4 marks

> In a freshwater pond, microscopic algae are eaten by water fleas. Water fleas are eaten by small fish, and small fish are eaten by pike.

## Mark scheme (4 marks)

1. A food chain shows the feeding relationships between organisms / shows the transfer of biomass from one organism to the next
2. Only around 10% of the energy / biomass is transferred from one trophic level to the next
3. Energy / biomass is lost at each trophic level through respiration (releasing heat) and in waste products such as faeces / urine / excretion
4. Because so little energy / biomass reaches the highest trophic level (pike), fewer organisms can be supported / there is insufficient energy / biomass to support a large population of pike

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Biology (4BI1)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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/a-pond-ecosystem-contains-the-following-40cd69d1) · Published by Druglandscape Ltd.