classification

• Species

  A group of similar organisms that can interbreed to produce fertile offspring
• Classification

  • Division of living organisms into groups based on their evolutionary relationships
  • Hierarchical, meaning that large groups are split into groups of decreasing size
  • Phylogenetic, meaning that organisms in the same group are more closely related
  • Discrete, an organism cannot belong to more than one group at the same taxonomic level
  • Each group is called a taxon
• Binomial name

  • A name in two parts, the first is the genus and the second is the species name
  • Organisms in the same genus are more closely related to each other than to organisms in a different genus
  • Conventionally, the binomial of an organism is italicised
• Binomial names are the same the world over, thus avoiding issues with local names and language differences
• Domains

  • Larger taxon than a kingdom
  • All organisms evolved along three separate lineages
• The three domains

  • Eubacteria - 'true' bacteria
  • Archaea - prokaryotic extremophiles
  • Eukarya - all eukaryotic organisms
• Extremophiles


  Organisms that live where environmental conditions are harsh, e.g. very high or low temperatures, acidic or alkaline environments, high salinity or pressure
• Taxonomic groups

  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• The five kingdoms

  • Prokaryotae
  • Animalia
  • Plantae
  • Fungi
  • Protoctista
• Prokaryotae


  • Lack a nucleus and membrane-bound organelles, have 70S ribosomes, circular DNA and a cell wall of peptidoglycan
• Animalia


  • Multicellular eukaryotes, no cell wall, heterotrophic and have nervous co-ordination
• Plantae


  • Multicellular eukaryotes, photosynthetic containing chloroplasts, have a cell wall of cellulose
• Fungi


  • Heterotrophic eukaryotes with a cell wall made of chitin; most are composed of thin threads called hyphae, reproduce by spores
• Protoctista


  • Mostly unicellular eukaryotes, algae have no tissue differentiation
• Morphology means looking at the shape and form of an organism
• Some organisms have similar morphology but are unrelated in evolutionary terms - this arises by convergent evolution
• Biochemical analysis such as DNA sequencing can overcome issues caused by convergent evolution
• Homologous structures


  Have the same structure but different functions, indicating that organisms are related
• Analogous structures


  Arise through convergent evolution, have the same function but different origin
• Biological polymers


  • Can be used to establish relatedness by comparing the sequences of subunits
  • The more differences in sequence, the less closely related two organisms are
  • Differences in sequence are due to mutations
  • Mutations in DNA can lead to differences in amino acid sequence of proteins
  • Differences can be used to construct a 'molecular clock' to show when a species or group diverged
• DNA fingerprint


  Banding pattern produced by gel electrophoresis, can be used for comparison