3.2.8 Principles of taxonomy

• Species


  group of organisms with similar physical and biochemical similarities that occupy the same ecological niche and that can breed to produce fertile offspring
• Levels of classification

  Kingdom, Phylum, Class, Order, Family, Genus, Species (as you go down the levels, there are fewer organisms in each group and the members of each group are more alike)

  
• Hierachy

  larger groups are subdivided into smaller groups, the groups at any one level do not overlap (e.g an organism cannot be in two kingdoms)
• Phylogenetic groups


  based on evolutionary relationships
• Phylogenetic trees

  the shorter the time two species shared a common ancestor, the more closely related the two species are

  
• What are the difficulties of defining species?

  species evolve over time i.e. individuals of one species develop into a new species, within a species there can be considerable variation (e.g. dog breeds), some species rarely reproduce sexually, members of the same species may be isolated (e.g. by oceans) so can never interbreed and may be classified as separate species, many species are extinct, when two different species breed they can produce infertile offspring, this offspring would be classed as a sterile species
• Binomial system

  two part name to define a species- Genus species (e.g. tigers are Panthera tigris, lions are Panthera leo)
• Taxonomy

  classification of organisms based on their similarities