# Explain why Carl Woese developed the three-domain system to replace the five kingdom classification system.

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

> Scientists have developed different systems for classifying living organisms over time. Carl Woese proposed the three-domain system, which groups all living organisms into three domains: Archaea, Bacteria and Eukarya.

## Mark scheme (4 marks)

1. The five kingdom system placed all prokaryotes into one kingdom (Prokaryotae), but the three-domain system separates prokaryotes into two distinct domains (Archaea and Bacteria)
2. Archaea are primitive bacteria that live in extreme environments and are sufficiently different from true bacteria to warrant their own domain
3. The Eukarya domain groups together all eukaryotic organisms, reflecting their common possession of a nucleus / membrane-bound organelles
4. The three-domain system is based on molecular / genetic evidence (e.g. differences in DNA or RNA sequences), making it a more accurate / scientific classification

## Key terms

- [three-domain system](https://www.gradenine.co.uk/glossary/three-domain-system)
- [five kingdom classification system](https://www.gradenine.co.uk/glossary/five-kingdom-classification-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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-carl-woese-developed-the-351c0191) · Published by Druglandscape Ltd.