# Explain why energy transfer between trophic levels in an ecosystem is never 100% efficient, and describe TWO consequences of this inefficiency for the structure of food chains.

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

> In a deciduous woodland ecosystem, measurements of biomass at each trophic level consistently show a dramatic reduction at each successive level. Ecologists use this data to construct pyramids of biomass and to model energy flow through the system.

## Mark scheme (4 marks)

1. Energy is lost at each trophic level because not all ingested material is assimilated — some is lost in faeces/egestion
2. Energy is lost through heat released during cellular respiration, so assimilated energy is not fully available to the next trophic level
3. Consequence 1: food chains are limited in length / typically no more than four or five trophic levels
4. Consequence 2: biomass / number of organisms decreases at each successive trophic level, producing a pyramid shape

## Key terms

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

## 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-3d10970b) · Published by Druglandscape Ltd.