Concept and use of a classification system



Organisms can be classified into groups by the features that they share.

  • species – a group of organisms that can reproduce to produce fertile offspring

  • the binomial system of naming species – an internationally agreed system in which the scientific name of an organism is made up of two parts showing the genus and species

    • the genus (always given a capital letter) 

    • and followed by the species (starting with a lowercase letter)

  • When typed, binomial names are always in italics (which indicates they are Latin) e.g. Homo sapiens

  • The sequence of classification is: Kingdom, Phylum, Class, Order, Family, Genus, Species

King Phillip Came Over For Good Spaghetti 

  • The sequence of classification is: Kingdom, Phylum, Class, Order, Family, Genus, Species

  • Kingdom -> Species = Similarity increases

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  • Organisms share features because they originally descend from a common ancestor

  • Originally, organisms were classified using morphology the overall form and shape of the organism, e.g. whether it had wings or legs; and anatomy the detailed body structure as determined by dissection

  • As technology advanced, microscopes, knowledge of biochemistry and eventually DNA sequencing allowed us to classify organisms using a more scientific approach

  • Studies of DNA sequences of different species show that the more similar the base sequences in the DNA of two species, the more closely related those two species are (and the more recent in time their common ancestor is)

  • This means that the base sequences in a mammal’s DNA are more closely related to all other mammals than to any other vertebrate groups

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DNA sequences show species relationship, CIE IGCSE Biology

DNA sequences can show how closely related different species are

  • The sequences above show that Brachinus armiger and Brachinus hirsutus are more closely related than any other species in the list as their DNA sequences are identical except for the last-but-one base (B.armiger has a T in that position whereas B.hirsutus has an A)

  • As DNA base sequences are used to code for amino acid sequences in proteins, the similarities in amino acid sequences can also be used to determine how closely related organisms are

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