# Explain why oxygen is described as the final electron acceptor in aerobic cell respiration.

> IB DP Biology Standard Level (2023 syllabus) — C1.2 Cell respiration · Explain · 4 marks

## Mark scheme (4 marks)

1. Electrons are passed along the electron transport chain (on the inner mitochondrial membrane) through a series of carrier proteins/molecules.
2. Oxygen accepts the electrons at the end of the electron transport chain (from the final carrier/cytochrome oxidase).
3. Oxygen combines with electrons and protons (H⁺) to form water.
4. If oxygen is absent, electrons cannot be passed along the chain, so the proton gradient cannot be maintained and ATP synthesis via ATP synthase stops / aerobic respiration cannot continue.

## Key terms

- [final electron acceptor](https://www.gradenine.co.uk/glossary/final-electron-acceptor)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](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-oxygen-is-described-as-cb635137) · Published by Druglandscape Ltd.