Hierarchy of the Taxa (AQA A Level Biology): Revision Note

Hierarchy of the taxa

• The hierarchical classification system of organisms in biology is used to organise and group similar organisms together so that they can be more easily understood

  • A hierarchical system is one in which larger groups contain smaller groups with no overlap between groups

• All taxonomic ranks or 'taxa' make up a 'taxonomic hierarchy'

• One hierarchy comprises the taxa: domain, kingdom, phylum, class, order, family, genus and species

• Species is the lowest taxonomic rank in the system and domains are the highest taxonomic rank in the system

  • Similar species can be grouped in a genus

  • Similar genera can be grouped in a family

  • Similar families can be grouped into an order

  • Similar orders can be grouped into a class

  • Similar classes can be grouped into a phylum

  • Similar phyla can be grouped into a kingdom

  • Similar kingdoms can be grouped into a domain

Example: homo sapians (humans)

• Humans are part of the domain of all eukaryotes, Eukarya. Eukarya is distinguishable from the other two domains, Bacteria and Archaea, which are both prokaryotic domains

• Just like the other domains, Eukarya contains the taxonomic hierarchy of kingdom, phylum, class, order, family, genus and species

• Below is an example the taxonomic hierarchy for homo sapians (humans)

Binomials

• Binomials are the scientific name of a species

  • A species is a group of organisms that can reproduce to produce fertile offspring

• It consists of the organism’s genus and species name in modern Latin

• For example, the binomial for humans is Homo sapiens and the binomial for dogs is Canis familiaris

• Binomials are extremely useful for scientists as they allow for species to be universally identified - the binomial for a species is the same across the entire globe