# A wildlife organisation is studying the carbon cycle in a woodland ecosystem. Explain how respiration and decomposition together return carbon dioxide to the atmosphere from the bodies of dead organisms.

> OCR A-Level Biology B — Advancing Biology (H422) — 4.2 Respiration · Explain · 5 marks

> When organisms in a woodland die, their bodies contain carbon stored as complex organic molecules. Microorganisms and other decomposers break down this material. The carbon cycle describes how carbon moves between living organisms and the environment.

## Mark scheme (5 marks)

1. Decomposers (microorganisms) feed on / break down dead organic matter
2. Decomposition converts complex organic molecules into simpler organic matter / releases carbon compounds
3. The decomposers (and other organisms) respire using glucose from the decomposed material
4. Respiration releases carbon dioxide into the atmosphere / air
5. This carbon dioxide can then be taken up by plants for photosynthesis, completing the carbon cycle

## Key terms

- [respiration](https://www.gradenine.co.uk/glossary/respiration)
- [decomposition](https://www.gradenine.co.uk/glossary/decomposition)
- [carbon cycle](https://www.gradenine.co.uk/glossary/carbon-cycle)

## Related

- [Revision notes for OCR A-Level Biology B — Advancing Biology (H422)](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-wildlife-organisation-is-studying-the-4d95ad00) · Published by Druglandscape Ltd.