# Explain why all animals, plants, fungi and protoctists are placed together in the domain Eukarya, whilst prokaryotic organisms are placed in separate domains in the three-domain system.

> Edexcel GCSE Biology (1BI0) — 4.2 Classification · Explain · 4 marks

## Mark scheme (4 marks)

1. All organisms in Eukarya are eukaryotic / have a nucleus (in their cells)
2. Prokaryotic organisms (bacteria and archaea) do not have a nucleus / have no membrane-bound nucleus
3. Bacteria and Archaea are placed in separate domains because they are sufficiently different from each other / have different RNA base sequences / Archaea are primitive bacteria found in extreme environments
4. The three-domain system groups organisms by fundamental cell structure / shared cellular features, which means the five-kingdom system's split of prokaryotes and eukaryotes is replaced by a grouping based on deeper evolutionary / molecular relationships

## Key terms

- [Eukarya](https://www.gradenine.co.uk/glossary/eukarya)
- [three-domain system](https://www.gradenine.co.uk/glossary/three-domain-system)

## Related

- [Revision notes for Edexcel GCSE Biology (1BI0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-all-animals-plants-fungi-7ecc379b) · Published by Druglandscape Ltd.