# Explain why the rate of ATP production in a cell would decrease significantly if the inner mitochondrial membrane became freely permeable to hydrogen ions (protons).

> OCR A-Level Biology A (H420) — 5.7 Respiration · Explain · 4 marks

> Researchers studying mitochondrial function discovered that certain toxins act by making the inner mitochondrial membrane permeable to hydrogen ions, effectively uncoupling electron transport from ATP synthesis.

## Mark scheme (4 marks)

1. The proton gradient (electrochemical / chemiosmotic gradient) across the inner mitochondrial membrane would be lost
2. Protons would no longer be forced through ATP synthase (chemiosmosis would not occur)
3. ATP synthase cannot catalyse the phosphorylation of ADP to ATP (oxidative phosphorylation does not occur)
4. Overall ATP yield is greatly reduced because oxidative phosphorylation accounts for the majority of ATP produced in aerobic respiration

## Key terms

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

## Related

- [Revision notes for OCR A-Level Biology A (H420)](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-why-the-rate-of-atp-1d48ca5b) · Published by Druglandscape Ltd.