# Explain how the chemiosmotic gradient across the inner mitochondrial membrane is established and used to synthesise ATP during aerobic respiration.

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

## Mark scheme (4 marks)

1. Electrons from reduced coenzymes (NADH/FADH₂) are passed along the electron transport chain, releasing energy
2. This energy is used by protein complexes to actively pump protons (H⁺) from the matrix into the intermembrane space, creating a proton/electrochemical gradient
3. Protons flow back into the matrix through ATP synthase (down the electrochemical gradient / by facilitated diffusion / chemiosmosis)
4. The flow of protons causes rotation of ATP synthase, driving the phosphorylation of ADP + Pᵢ to produce ATP (oxidative phosphorylation)

## Key terms

- [chemiosmotic gradient](https://www.gradenine.co.uk/glossary/chemiosmotic-gradient)
- [inner mitochondrial membrane](https://www.gradenine.co.uk/glossary/inner-mitochondrial-membrane)

## 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)
- [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-how-the-chemiosmotic-gradient-across-07d76440) · Published by Druglandscape Ltd.