Describe how the classification of living organisms changed when Carl Woese developed the three-domain system.

AQA GCSE Biology (8461) — 4.6.4 Classification of living organisms · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

The Linnaean system divided all life into hierarchical kingdoms, phyla, classes, orders, families, genera and species.

Carl Woese introduced a new method based on ribosomal RNA sequences.

He showed that organisms could be grouped into three domains: Archaea, Bacteria and Eukaryota.

Archaea are primitive, single‑cell organisms that live in extreme environments and are now recognised as distinct from true Bacteria.

Examiner tips

Use the exact terms ‘Linnaean system’, ‘three‑domain system’, ‘Archaea’, ‘Bacteria’, ‘Eukaryota’.
Show the change from kingdoms to domains and explain the new grouping of Archaea.
Keep each point short and to the point to match the 4‑mark structure.

Common mistakes

Confusing ‘kingdoms’ with ‘domains’; writing only ‘domains’ without mentioning the Linnaean system.
Using vague phrases like ‘different method’ without naming ribosomal RNA or the three domains.
Omitting that Archaea are separate from true Bacteria or that they are extremophiles.

Mark scheme (4 marks)

The Linnaean system classified organisms into kingdoms (e.g. kingdom, phylum, class, order, family, genus, species)
Carl Woese developed the three-domain system as a new / different method of classification
Organisms are now grouped into three domains: Archaea, Bacteria and Eukaryota
Archaea are primitive bacteria / microorganisms that live in extreme environments, recognised as separate from (true) Bacteria

Key terms in this question

three-domain system · classification