# Explain how the ultrastructure of a mitochondrion is related to its role in aerobic cellular respiration.

> IB DP Biology Standard Level (2023 syllabus) — A2.2 Cell structure · Explain · 4 marks

## Mark scheme (4 marks)

1. The inner mitochondrial membrane is folded into cristae, which increases the surface area available for the electron transport chain / ATP synthase / oxidative phosphorylation.
2. The matrix is the site of the Krebs cycle / contains enzymes for the Krebs cycle and pyruvate oxidation, so reactions of aerobic respiration occur within the organelle.
3. The double membrane / two membranes create a compartment (intermembrane space) that allows a proton / H⁺ gradient to be established, which drives ATP synthesis via chemiosmosis.
4. Mitochondria contain their own circular DNA and ribosomes, allowing synthesis of some of the proteins required for respiration / self-replication, consistent with endosymbiotic origin.

## Key terms

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

## 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-the-ultrastructure-of-a-7486a4e4) · Published by Druglandscape Ltd.