C: diversity and classification

• phylogeny:

  • the study of the evolutionary history of groups of organisms
  • tells us who is related to whom and how closely realted they are
• all organisms have evolved from shared common ancestors (relatives) which can be shown on a phylogenetic tree:

  • shows the relationship between members of a family
  • first branch represents a common ancestor to all family members (extinct)
  • each of the following branch points represents another common ancestor from which a different group diverged
  • closely related species diverged away from each other most recently
• Taxonomy - the science of classification

  • involves naming organisms and organising them into groups
  • makes it easier to identify and study them
  • scientists take into account phylogeny when classifying organisms and group organisms according to their evolutionary relationships
• there are 8 levels of groups used to classify organisms - called taxa

  • each group is called a taxon
  • groups arranged in a hierarchy
  • largest group at the top, smallest groups at the bottom
  • organisms can only belong to one group at each level in the hierarchy - no overlap
• Fist group = domains

  • eukarya
  • bacteria
  • archaea
• related organisms in a domain then sorted into slightly smaller groups - kingdoms

  e.g. animal kingdon
• more closely related organisms from that kingdom then organised into a phylum, then class
• domain

  kingdom

  phylum

  class

  order

  family

  genus

  species
• as you move down the hierarchy there are more groups at each level but fewer organisms in each group

  organisms in each group become more closely related
• the hierarchy ends with species - the groups that contain only one type of organism
• a species is a group of similar organisms able to reproduce to give fertile offspring
• The binomial system - nomenclature used for classification of organisms.

  all organisms are given one internationally accepted scientific name in latin that has 2 parts
• • first part = the genus name and has a capital letter
  • second part = the species name and begins with a lower case letter
  • always written in italics/ underlined if hand written
• giving organisms a scientific name allows scientists to communicate about organisms in a standard way - helps avoid the confusion of using common names