# A marine food chain contains the following organisms: phytoplankton → krill → mackerel → dolphin. Describe what is meant by a trophic level and explain why the dolphin, as a tertiary consumer, has the least biomass available to it compared with organisms at lower trophic levels.

> AQA GCSE Biology (8461) — 4.7.4 Trophic levels in an ecosystem (Bio only) · Describe and Explain · 4 marks

## Mark scheme (4 marks)

1. A trophic level is the position of an organism in a food chain
2. Biomass is lost at each trophic level / not all biomass is transferred to the next level
3. Biomass is used for respiration / movement / heat loss / metabolic processes by organisms at each trophic level
4. The dolphin is at trophic level 4 so biomass has been lost across three previous trophic levels, meaning very little biomass remains available

## Key terms

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

## Related

- [Revision notes for AQA GCSE Biology (8461)](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-marine-food-chain-contains-the-03ce3b06) · Published by Druglandscape Ltd.