# Explain why the number of organisms at each trophic level decreases as you move along a food chain from producer to tertiary consumer.

> AQA GCSE Biology (8461) — 4.7.2 Organisation of an ecosystem · Explain · 4 marks

## Mark scheme (4 marks)

1. Biomass (or energy) is lost at each trophic level
2. Biomass is used for respiration / movement / heat release by the organism
3. Biomass is also lost in waste materials such as faeces / urine / uneaten parts
4. Less biomass is available to support fewer / smaller organisms at higher trophic levels

## Key terms

- [trophic level](https://www.gradenine.co.uk/glossary/trophic-level)
- [producer](https://www.gradenine.co.uk/glossary/producer)
- [tertiary consumer](https://www.gradenine.co.uk/glossary/tertiary-consumer)
- [food chain](https://www.gradenine.co.uk/glossary/food-chain)

## Related

- [Revision notes for AQA GCSE Biology (8461)](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-number-of-organisms-d989ad55) · Published by Druglandscape Ltd.