Classification
Biology: AQA A Level, topic 4.5.3
Classification
Classification in biology involves the identifying, naming and sorting of organisms in a process called taxonomy. Organisms are classified into groups called taxa.
Taxa
- Closely related organisms are grouped together into groups called taxa (singular = taxon).
- The phylogeny of organisms (their evolutionary relationships) is important for determining which taxa an organism is a part of.
Hierarchy
- Each taxon is arranged into a hierarchy.
- The hierarchy divides into smaller, more specific taxa at each level.
- There is no overlap between taxa at the same level.
- Organisms can only belong to one taxon at each level.
Stages in the hierarchy
- Organisms are arranged into the following hierachy, designed by Carl Linnaeus:
- Domain.
- Kingdom.
- Phylum.
- Class.
- Order.
- Family.
- Genus.
- Species.
E.g. Humans
- Humans can be classified in the hierarchy system as:
- Domain = Eukaryota.
- Kingdom = Animalia.
- Phylum = Chordata.
- Class = Mammalia.
- Order = Primates.
- Family = Hominidae.
- Genus = Homo.
- Species = Homo sapiens.
Binomial names
- The naming system used in classification is called the binomial system.
- The binomial system consists of the genus and the species of an organism.
- The names are always written in italics if they are typed or they are underlined if hand-written.
- E.g. The binomial name for humans is Homo sapiens.
Test yourself on Classification
Which of these is NOT a taxa in Linnaeus' hierarchy?
Which of the following statements about classification are true?