# Explain how oxygen acts as the final electron acceptor in aerobic cell respiration and why its absence prevents continued ATP production via oxidative phosphorylation.

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

## Mark scheme (4 marks)

1. Electrons pass along the electron transport chain (ETC) through carrier proteins, losing energy at each step.
2. Oxygen accepts electrons (and protons/H⁺) at the end of the ETC, forming water.
3. Without oxygen, electrons accumulate / cannot leave the ETC, so the chain becomes blocked / reduced carriers cannot be re-oxidised.
4. Because the proton gradient across the inner mitochondrial membrane cannot be maintained, ATP synthase cannot synthesise ATP via oxidative phosphorylation.

## Key terms

- [oxidative phosphorylation](https://www.gradenine.co.uk/glossary/oxidative-phosphorylation)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-oxygen-acts-as-the-40a9ba7c) · Published by Druglandscape Ltd.