# Explain why energy transfer between trophic levels in an ecosystem is never 100% efficient.

> OCR A-Level Biology A (H420) — 6.5 Ecosystems · Explain · 4 marks

> In a temperate grassland ecosystem, ecologists measured the energy content of producers and primary consumers. They found that only approximately 10% of the energy stored in the producers was incorporated into the biomass of the primary consumers.

## Mark scheme (4 marks)

1. Some energy is lost through heat released during respiration by organisms at each trophic level
2. Not all ingested material is assimilated — some is lost in faeces / egested
3. Some energy is lost via excretion of nitrogenous waste products such as urea
4. Not all biomass at a trophic level is consumed / some organisms die and are broken down by decomposers rather than being eaten by the next trophic level

## Key terms

- [trophic levels](https://www.gradenine.co.uk/glossary/trophic-levels)
- [ecosystem](https://www.gradenine.co.uk/glossary/ecosystem)

## Related

- [Revision notes for OCR A-Level Biology A (H420)](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-energy-transfer-between-trophic-59cd875e) · Published by Druglandscape Ltd.