Definitions of Species (CIE A Level Biology)

• 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 referring to, 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 italicised 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