AQA AS Biology

Revision Notes

4.5.3 Hierarchy of the Taxa

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
  • There are several taxonomic ranks that exist
    • All taxonomic ranks or ‘taxa’ make up a ‘taxonomic hierarchy’
  • Species is the lowest taxonomic rank in the system
    • Similar species can be grouped in a genus
    • Similar genuses 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
  • Domains are the highest taxonomic rank in the system
  • There are a few different rhymes that exist to help you remember the different ranks in the taxonomic classification system. You can always make up your own but the one below is super helpful!
  • The first letters of all the different ranks below the domains can be remembered as:
    • Kings Play Chess On Fancy Gold Squares
    • Kingdom Phylum Class Order Family Genus Species

Classification of an organism in the Eukarya domain

  • Eukarya is the domain of all eukaryotes, distinguishable from 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
  • A wolf is an example of an organism in the Eukarya domain
  • It can be classified further into its kingdom, phylum, class, order, genus and species
  • A wolf belongs to the following taxonomic groups:
    • Domain: Eukarya
    • Kingdom: Animalia
    • Phylum: Chordata
    • Class: Mammalia
    • Order: Carnivora
    • Family: Canidae
    • Genus: Canis
    • Species Canis lupus
  • The Hibiscus rosa-sinensis is another example of of an organism in the eukarya domain
  • It is a colourful flowering plant
  • It belongs to the following taxonomic groups:
    • Domain: Eukarya
    • Kingdom: Plantae
    • Phylum: Angiospermae
    • Class: Dicotyledonae
    • Order: Malvales
    • Family: Malvaceae
    • Genus: Hibiscus
    • Species: Hibiscus rosa-sinensis

A classification table

Example of A Classification Table, downloadable AS & A Level Biology revision notes

Binomials

  • A species is a group of organisms that are able to reproduce to produce fertile offspring
  • Binomials are the scientific name of a species
  • 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

Exam Tip

The binomial for a species is always typed in italics or underlined when handwritten.

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