# Explain how evidence from the replication of mitochondria supports the endosymbiotic theory for the origin of eukaryotic cells.

> IB DP Biology Higher Level (2023 syllabus) — A2.1 Origins of cells · Explain · 4 marks

## Mark scheme (4 marks)

1. Mitochondria divide by binary fission, the same process used by prokaryotes / bacteria.
2. Mitochondria are never synthesised de novo / cannot arise from non-mitochondrial material; new mitochondria only form from pre-existing mitochondria.
3. This mirrors the situation in endosymbiosis, in which the ancestral prokaryotic endosymbiont would have replicated independently within the host cell.
4. Mitochondria possess their own circular DNA and 70S ribosomes, meaning they can carry out semi-autonomous replication / protein synthesis, consistent with a prokaryotic ancestor.

## Key terms

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

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-evidence-from-the-replication-79c7356b) · Published by Druglandscape Ltd.