The three domain system
Laura Armstrong & Joe Wolfensohn
Teachers
Recall Questions
This topic requires prior knowledge of classification and binomial naming.
What are the 7 taxa in the classification hierarchy?
Kingdom, Phylum, Class, Order, Family, Genus, Species.
Who developed this classification system?
Carl Linnaeus.
What does the two part scientific name include?
The genus name followed by the species name.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains the three domain system, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
Remember The Linnaean Classification System?
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Kingdom
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Phylum
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Class
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Order
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Family
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Genus
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Species
This hierarchy goes from larger, broader groups to smaller, more specific ones.
This has since been adapted based on new evidence.
Scientific Developments and Classification
Classification systems have changed and developed over time.
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They were originally based on appearance and structure of organisms only.
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As microscope technology improved, scientists could see cells and their sub-cellular structures.
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Later, DNA and biochemical analysis showed more accurate relationships between organisms.
- We have more information on evolutionary relationships and shared common ancestry from studying DNA and genes.
New theories replace older ones if more evidence supports them.
The Three-Domain System
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Proposed in the 1990s by Carl Woese.
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Based on differences in biochemical processes and genetic analysis of DNA.
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Replaces the old “five kingdoms” with three domains:
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Archaea – primitive bacteria, often found in extreme environments (e.g., hot springs).
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Prokaryota – true bacteria.
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Eukaryota – all organisms with complex cells, including protists, fungi, plants and animals. These organisms are called eukaryotes as their cells have a nucleus as well as other organelles / sub-cellular structures.
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Domain is the largest taxon and sits above kingdom in the new hierarchy:
- Domain
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
Key Terms
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Classification – Grouping organisms by similarities in characteristics or genes.
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Domain – The highest level of classification in modern biology.
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Carl Linnaeus – Scientist who developed the traditional classification system.
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Carl Woese – Scientist who proposed the modern three-domain system of classification.
No answer provided.
Exam Tip
Learn the names of the scientists! Carl Linnaeus developed the original 7 Kingdom system of classification. Whilst Carl Woese developed the more recent three domain system.
Use the pneumonic Delicious King Prawn Curry Or Fat Greasy Sausages to remember the order of the taxa in the classification hierarchy! Delicious is for the domain which was added above the Kingdom.
No answer provided.
Practice Question
Carl Woese proposed the ‘three-domain system’ of classification.
Which domain are insects in? (1)
Eukaryota / eukaryote
(Insects are animals, made up of animal cells with nuclei)
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!