# A grassland ecosystem contains grass, grasshoppers, frogs and herons arranged in a food chain. A scientist measures the biomass at each trophic level and finds that the biomass of grass is very much greater than the biomass of herons. Explain why the biomass of herons is so much lower than the biomass of grass.

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

> In a grassland food chain: grass → grasshoppers → frogs → herons. The total biomass of grass measured across the ecosystem is approximately 10 000 kg. The total biomass of herons in the same ecosystem is approximately 10 kg.

## Mark scheme (5 marks)

1. Energy is lost at each trophic level / as you move along the food chain
2. Energy is used in respiration by organisms at each trophic level
3. Energy is lost in waste products such as faeces / urine / undigested material
4. Only a small proportion of energy / biomass is passed on to the next trophic level (approximately 10%)
5. Because energy is lost at each of the four trophic levels, by the time energy reaches the herons very little biomass / energy remains, so herons have a much lower biomass than grass

## Key terms

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

## 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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Source: [GradeNine](https://www.gradenine.co.uk/q/a-grassland-ecosystem-contains-grass-grasshoppers-773c48ff) · Published by Druglandscape Ltd.