# Explain how bacteria, archaea, and eukaryotes are distinguished from one another at the domain level of classification.

> IB DP Biology Standard Level (2023 syllabus) — A3.1 Diversity of organisms · Explain · 4 marks

## Mark scheme (4 marks)

1. Bacteria and Archaea are both prokaryotes (lacking a membrane-bound nucleus), whereas Eukaryotes possess a membrane-bound nucleus.
2. Archaea are distinguished from Bacteria by differences in their cell membrane composition, specifically the presence of ether-linked lipids in Archaea (compared to ester-linked lipids in Bacteria).
3. Bacteria have peptidoglycan in their cell walls, whereas Archaea lack peptidoglycan.
4. Molecular evidence (such as rRNA / ribosomal gene sequence comparisons) shows that Archaea are more closely related to Eukaryotes than to Bacteria, justifying three separate domains.

## Key terms

- [domain](https://www.gradenine.co.uk/glossary/domain)
- [Archaea](https://www.gradenine.co.uk/glossary/archaea)

## 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-bacteria-archaea-and-eukaryotes-80a5a82b) · Published by Druglandscape Ltd.