# Explain why the efficiency of energy transfer between trophic levels is important when considering the sustainability of different types of farming.

> AQA A-Level Biology (7402) — 3.5.3 Energy and Ecosystems · Explain · 5 marks

> Salmon farms raise fish in large enclosures and feed them on smaller fish caught from the sea. Some farmers are switching to plant-based feeds for their salmon instead.

## Mark scheme (5 marks)

1. Only a small percentage (approximately 10%) of energy is transferred from one trophic level to the next
2. Energy is lost through processes such as respiration / movement / heat loss / waste products (excretion/faeces)
3. Feeding salmon on smaller fish means there is an extra trophic level, so more energy is lost overall
4. Using plant-based feed removes a trophic level, so more energy reaches the salmon / less energy is wasted
5. Plant-based feeds are therefore more sustainable because fewer resources / less land / fewer wild fish are needed to produce the same amount of salmon biomass

## Key terms

- [trophic level](https://www.gradenine.co.uk/glossary/trophic-level)
- [energy transfer](https://www.gradenine.co.uk/glossary/energy-transfer)
- [sustainability](https://www.gradenine.co.uk/glossary/sustainability)

## Related

- [Revision notes for AQA A-Level Biology (7402)](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/explain-why-the-efficiency-of-energy-5c788740) · Published by Druglandscape Ltd.