A level Biology B · Edexcel 9BI0 · Topic 3A
Classification
Key points
- The taxonomic hierarchy: domain, kingdom, phylum, class, order, family, genus, species.
- Binomial names give genus then species (e.g. Homo sapiens), giving one universal name for each species.
- A species is a group of organisms that can interbreed to produce fertile offspring.
- The three-domain system (Bacteria, Archaea, Eukarya) is based on molecular evidence such as rRNA sequences, membrane lipids and cell wall chemistry; it replaced the five-kingdom system.
- Comparing DNA base sequences, amino acid sequences and immunological responses shows how closely related species are.
- New evidence is shared through peer review and conferences, so classifications change as scientists agree on findings.
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Classification sorts organisms into groups so that scientists everywhere can name, identify and study them consistently. Modern classification tries to group organisms by how closely they are related through evolution, and molecular…
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