OCR AS Biology

Revision Notes

4.3.1 Classification of Species

Classification of Species

  • Taxonomy is the practice of biological classification
  • The biological classification system enables us to arrange species into groups based on their evolutionary origins and relationships
  • In this hierarchical system there is no overlap between groups and each group is called a taxon (plural taxa)
  • By grouping organisms into taxa it can make them easier to understand and remember
  • There are several different ranks or levels within the hierarchical classification system used in biology
    • Multiple smaller taxa can be put into one larger taxon

Hierarchical classification

  • 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 (plural genera)
    • 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 (plural phyla)
    • 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. A couple of examples are given below but you could always make up your own!
  • The first letters of all the different ranks below the domains can be remembered as:
    • Kings Play Chess On Fancy Gold Squares
    • Kittens Pounce Clumsily On Furry Green Spiders
    • Kingdom Phylum Class Order Family Genus Species

The hierarchical classification system – The higher ranks contain more organisms with less similarity between them. The lower ranks contain fewer organisms with more similarity between them.

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

The classification system is organised within the eukarya domain – Note there are missing groups at each rank

  • 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 classification of a Wolf.

  • The Hibiscus rosa-sinensis (a colourful flowering plant) is another example of an organism in the eukarya domain
  • 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

A Classification Table_2, downloadable AS & A Level Biology revision notes

Exam Tip

The name of a species always consists of two words: the genus and species. This means when provided with the Latin name of a species you are automatically provided with information about the last two taxonomic ranks that the organism belongs to. Remember this when being asked to show or explain the classification of an organism in the exam.


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