Classification of Organisms

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Classification of Organisms

Phylogenetic classifcation

Phylogenetic classification classifies organisms based on their evolutionary history, this means that closely related organisms are grouped together. All organisms have evolved from shared common ancestors, so organisms which are in the same group have a more recent common ancestor with each other than with organisms not in their group. If organisms are closely related they will typically show physical similarities as displayed in tigers, lions and cheetahs.

A phlogenetic tree can show how all organisms have evolevd from shared common ancestors.



Taxonomy is the science of classification. It involves naming organisms and organising them into groups. 

There are eight levels of groups used to classify organisms. These groups are called taxa. Each group is therefore a taxon. The groups are arranged in a hierarchy, with the largest groups at the top and the smallest at the bottoms. The organisms can only belong to one group at each level in the hierarchy, they can only be in one taxon.

The hiearchy of biological classification is:

  • Domain
  • Kingdom - there are 5
  • Phylum - organisms in each phyla have radically different body plasn
  • Class - diversity within the phyla allows a further division into classes
  • Order - each class is divided into orders of organisms that have additional features in common
  • Family - at this level the difefrences are less obvious
  • Genus - each family is further sub-divided into genera
  • Species

Organisms are sorted into three large taxas called domains. A


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