4.3.1 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: 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: rosa-sinensis

A Classification Table