# Explain how chemiosmosis results in the synthesis of ATP during 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), releasing energy.
2. This energy is used to actively pump protons (H⁺ ions) from the mitochondrial matrix into the intermembrane space, establishing a proton gradient.
3. Protons flow back into the matrix down their concentration gradient through ATP synthase.
4. The flow of protons through ATP synthase drives the phosphorylation of ADP to ATP (oxidative phosphorylation).

## Key terms

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

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-chemiosmosis-results-in-the-a3a36d84) · Published by Druglandscape Ltd.