# A coral reef ecosystem contains algae, small fish, large fish and sharks. A student claims that the shark population can never be as large as the algae population in this ecosystem. Explain why the student's claim is correct, with reference to energy flow through the ecosystem.

> Pearson Edexcel A-Level Biology A (9BI0) — 3.2 Energy flow and ecosystems · Explain · 5 marks

> In a coral reef food chain, algae are eaten by small fish, which are eaten by large fish, which are eaten by sharks.

## Mark scheme (5 marks)

1. Algae photosynthesise / use light energy to produce biomass, making them the producers / first trophic level
2. Energy is lost at each trophic level
3. Energy is lost through heat released during respiration / movement / maintaining body temperature
4. Energy is also lost in waste products / undigested material / faeces / urine
5. Because less energy is available at each successive trophic level, less biomass can be supported, so the shark population (top predator) must be smaller than the algae population

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](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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