# A saltmarsh ecosystem contains the following food chain: cordgrass → marsh grasshoppers → marsh wrens → marsh hawks. Explain why the marsh hawk population can only be supported by a large number of cordgrass plants.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 3.2 Energy flow and ecosystems · Explain · 5 marks

> In a saltmarsh ecosystem, energy is transferred through a food chain. At each stage, only approximately 10% of the energy from one trophic level is transferred to the next.

## Mark scheme (5 marks)

1. Energy is lost at each trophic level / between each stage of the food chain
2. Energy is lost through heat released during respiration
3. Energy is also lost in waste products such as urine or faeces / in materials not consumed or digested
4. Only approximately 10% of energy is passed from one trophic level to the next, so by the time energy reaches the marsh hawk very little energy remains
5. Therefore a large biomass / large number of cordgrass plants is needed at the start to provide enough energy to support the marsh hawk population

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](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/a-saltmarsh-ecosystem-contains-the-following-e5ada24c) · Published by Druglandscape Ltd.