# Explain how the three-domain system differs from the five kingdom classification system in the way it groups living organisms.

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

> Scientists have used different systems over time to classify all living organisms. Carl Woese proposed the three-domain system after analysing the genetic material of a wide range of organisms, including bacteria found in extreme environments.

## Mark scheme (4 marks)

1. The three-domain system groups organisms into three domains (Archaea, Bacteria and Eukarya), whereas the five kingdom system groups organisms into five kingdoms.
2. The three-domain system separates Archaea (primitive bacteria living in extreme environments) from true Bacteria as distinct domains, whereas the five kingdom system placed all bacteria together in Prokaryotae.
3. The Eukarya domain in the three-domain system includes all eukaryotic organisms, which were previously spread across multiple kingdoms (Animalia, Fungi, Plantae, Protoctista) in the five kingdom system.
4. The three-domain system is based on genetic / molecular evidence (DNA analysis), making it more accurate / reflecting evolutionary relationships more closely than the five kingdom system, which was based primarily on observable characteristics.

## 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

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-three-domain-system-differs-7e5f1aa3) · Published by Druglandscape Ltd.