Classification of living organisms

Linnaean system of classification

Living organisms are classified into groups depending on their structure and characteristics. This system was developed in the eighteenth century by Carl Linnaeus.

The classification of species allows the subdivision of living organisms into smaller and more specialised groups.

Kingdoms

The first division of living things in the classification system is to put them into one of five kingdoms.

The five kingdoms are:

  • animals (all multicellular animals)
  • plants (all green plants)
  • fungi (moulds, mushrooms, yeast)
  • protists (Amoeba, Chlorella and Plasmodium)
  • prokaryotes (bacteria, blue-green algae)

Further divisions

Living things can then be ranked according to:

Phylum follows Kingdoms and has many different organisms, including three examples below:

  • Chordata, which have backbones
  • Arthropod, which have jointed legs and an exoskeleton
  • Annelids, which are segmented worms

Class is an additional sub-division, which for example, results in the Chordata phylum being divided into:

  • Mammals
  • Birds
  • Amphibians
  • Fish
  • Reptiles

Order follows class and as an example, mammals can be further sub-divide into a variety of different groups such as:

  • Carnivores
  • Primates

Orders are broken down into families. Here are a few examples of which carnivores can be divided into:

  • Canidae - dogs
  • Felidae - cats

Genus, the Felidae family can be further sub-divided into four genus examples:

  • Acinonyx - cheetah
  • Panthera - lion and tiger
  • Neofelis - clouded leopard
  • Felis - domestic cats

Species is the final classification stage, and the genus Panthera can be divided into:

  • Panthera leo (lion)
  • Panthera tigris (tiger)

As an example, the complete breakdown of the classification of lions:

  • kingdom - animal
  • phylum - vertebrate
  • class - mammal
  • order - carnivorous
  • family - cat
  • genus - big cat
  • species - lion

There are many ways to remember this order, for example using the mnemonic:

Living organisms are classified into groups depending on their structure and characteristics. This system was developed in the eighteenth century by Carl Linnaeus.

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the European Robin
Erithacus rubecula, the European Robin

The binomial system of naming species uses Latin words. Each name has two parts, the genus and the species. For example, human beings belong to the genus Homo, and our species is sapiens - so the scientific name is Homo sapiens.

The binomial system is important because it allows scientists to accurately identify individual species. For example, the European robin is Erithacus rubecula. It is much smaller than the American robin, Turdus migratorius, which belongs to a different genus.

The grouping of families was added to allow the large number of new species to be included in this system. Linnaeus' original ideas have been adapted, but continued to be accepted and as new species are identified they can be fitted into the current classification system.

Originally, Linnaeus couldn't distinguish between different types of organisms such as algae, lichens, fungi, mosses and ferns. The inability to examine such organisms in detail made separation of these difficult at the time.

As more scientific equipment became available it allowed scientists to examine organisms in more detail and note important features, such as the identification of sex organs. This allowed more divisions to be created, and with the advancement of technology, this allowed the development of Linnaeus's classification system.