AQA Biology Unit 2: 14 Classification


14.1 Classification

  • Classification is the organisation of living organisms into group
  • A species is the basic unit of classification and is a group of similar organisms that can breed together to produce fertile offspring

Naming Species: Binomial System

  • The Binomial System features:
    • A universal system based on Latin or Greek names
    • The generic name (first name) is the genus the organism belongs to
    • The specific name (second name) is the species
    • The first letter of the generic name is in upper case and the specific name in lower case
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Classification Cont

Grouping Species

  • Taxonomy: The theory and practice of biological classification
  • There are two main forms of classification:
    • Artificial Classification: divides organisms according to useful differences at the time such as colour or size. The characteristics are analogous as they have the same function but not the same evolutionary origins
    • Natural Classification: Based on evolutionary relationships between organisms and ancestors, classifies species into groups using shared features from their ancestors and arranges the groups into a hierarchy
  • Relationships in the natural classification are based on homologous characteristics
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Classification Cont

Organising Groups of Species (Taxonomy)

  • Taxon: each group within a natural biological classification
  • The hierarchical order (taxonomic ranks) is based on evolutionary line of descents
  • The ranks are:
    • Kingdom
    • Phylum
    • Class
    • Order
    • Family
    • Genus
    • Species
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Classification Cont


  • Is the evolutionary relationship between organisms
  • The phylogeny of an organism reflects the evolutionary branch that it led up to
  • The relationship with different species is shown in a phylogenetic tree where the oldest species are at the bottom of the tree
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