# Explain the evidence that supports the endosymbiotic origin of mitochondria in eukaryotic cells.

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

## Mark scheme (4 marks)

1. Mitochondria have their own circular DNA, similar to that found in prokaryotes, suggesting a bacterial ancestor.
2. Mitochondria have their own 70S ribosomes, which are the same size as prokaryotic ribosomes rather than the 80S ribosomes found in the eukaryotic cytoplasm.
3. Mitochondria are surrounded by a double membrane, with the inner membrane consistent with an engulfed bacterium that retained its own membrane inside the host cell's membrane.
4. Mitochondria reproduce by binary fission independently of the cell cycle, as prokaryotes do, rather than by mitosis.

## Key terms

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

## 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-the-evidence-that-supports-the-b435e1fc) · Published by Druglandscape Ltd.