Classification of living organisms

• Three domain classification system

  • Archaea (primitive bacteria found in extreme conditions)
  • Bacteria (true bacteria like those in the human digestive system)
  • Eukaryota (animals, plants, fungi, protists like amoeba)
• Using evolutionary trees to show how closely related organisms are

  1. Classify living organisms based on data like DNA

  2. Use fossils to classify extinct organisms (but fossil records are often incomplete)
• Linnaeus divided all living organisms into two kingdoms: animal kingdom and plant kingdom
• Linnaeus' classification categories


  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• Linnaeus' classification system is based on characteristics that can be observed, like body shape and number of toes
• Binomial system names organisms using their genus and species
• Advances in biology like microscopes and biochemistry analysis have improved classification beyond Linnaeus' system
• Evolutionary trees show how closely related organisms are, with a common ancestor