CIE A Level Biology

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First teaching 2020

Last exams 2024

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18.1.1 Definitions of Species

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Definitions of Species

  • Scientists have been classifying organisms into species for hundreds of years, in order to investigate the diversity of life that exists today and in the past
  • There is difficulty in determining whether new organisms discovered belong to an existing species, or a new one
  • This is because the most widely accepted definition of a species is:
    • A group of organisms with similar morphological and physiological features that able to breed together and produce fertile offspring

  • This is the biological species concept, and is reliant on determining whether interbreeding produces fertile offspring - this is difficult and time-consuming to determine in practice
  • However there are other discriminating factors that scientists can use to group similar organisms together

Morphological species concept

  • In the past, most scientists described organisms by their physical features (morphology) as these can be more easily observed
  • They group together organisms that share many physical features that distinguish them from other species
  • This is the morphological species concept

Ecological species concept

  • When there is a population of similar organisms living in the same area at the same time, they can be described as an ecological species
  • This is the ecological species concept

Naming species

  • Species are often given common names, but in order to avoid confusion about what group of organisms scientists are talking about, all species are given a two-part scientific name using the binomial system
  • This naming convention was developed and established by the Swedish scientist Carl Linnaeus in the 18th Century
  • The first part of the name is the genus that the species belongs to; this is a group of very similar organisms
  • The second part of the name is specific and unique to a single group of organisms that are identified as a species (and occasionally there may be a third name)
  • The binomial name is always italicized in writing (or underlined if it is not possible to italicise)
  • For example:
    • The most commonly known yeast is Saccharomyces cerevisiae
    • It is common to abbreviate the genus name: S. cerevisiae
    • Saccharomyces paradoxus is another species of that is a member of the same genus as cerevisiae

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Lára

Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.