# Explain how the structure of the inner mitochondrial membrane is adapted to maximise the efficiency of ATP synthesis during aerobic respiration.

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

## Mark scheme (4 marks)

1. The inner mitochondrial membrane is highly folded into cristae, greatly increasing the surface area available for the electron transport chain and ATP synthase complexes.
2. The inner membrane is impermeable to protons (H⁺/hydrogen ions), so a proton gradient can be maintained across it, which is essential for chemiosmosis.
3. Proteins of the electron transport chain (e.g. NADH dehydrogenase / cytochrome complexes) are embedded in the inner membrane and pump protons from the matrix into the intermembrane space, establishing the electrochemical / proton gradient.
4. ATP synthase is embedded in the inner membrane and uses the flow of protons back into the matrix (down their electrochemical gradient) to drive the phosphorylation of ADP to ATP.

## Key terms

- [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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-structure-of-the-ec9b0eb7) · Published by Druglandscape Ltd.