Classification of Living Organisms: Updated System
Biology: AQA GCSE Higher, topic 6.4.3
The Three-Domain System
The ‘three-domain system’ was proposed by Carl Woese and classifies organisms based on chemical analysis:
Archaea
- Primitive bacteria, many of which are extremophiles (i.e. live in extreme environments).
Bacteria
- True bacteria.
Eukaryota
- Organisms that possess complex subcellular structures (e.g. protists, fungi, plants and animals).
Test yourself on Classification of Living Organisms: Updated System
Why are protists, fungi, plants and animals all classified together in the Eukaryota domain?
Two organisms look very different but have a very similar chemical makeup. On what basis would the three-domain system still classify them in the same domain?
An organism survives in an environment so extreme that most other life forms would die there. Based on the three-domain system, which domain would this organism most likely belong to?
Archaea and Bacteria are both simple, single-celled organisms, yet the three-domain system places them in separate domains. What is the key difference between them?
Why would a fungus and a bacterium never be classified in the same domain under the three-domain system?