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HBIO2 > Classification
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Classification

  • Nomenclature: naming of organisms
  • Binomial: biological name of an organism → Genus species (eg Homo sapiens)
  • Taxon: set of organisms within a category / taxonomy / study of biological classification
  • Different levels of taxons: species, genus, family, order, class, phylum, kingdom
    • Right side of spectrum → highest number of species
    • Left side of spectrum → most similar organisms
  • Five Kingdoms:
    • Prokaryotae
    • Protoctista
    • Fungi
    • Plantae
    • Animalia
  • Background Knowledge
    • There is a new three-domain system:
      • Domain Eukarya - contains the four kingdoms
        • Animalia
        • Pkantae
        • Fungi
        • Protista
      • Domain Archaea
      • Domain Bacteria
  • Unicellular: Single cell; Colonial: Groups of cells; Multicellular: Many cells
  • Autotrophs produce energy from inorganic sources
    • Phototrophs from photosynthesis/sunlight
    • Chemotrophs from simple inorganic (oxidative) processes
  • Heterotrophs digest and absorb organic molecules
  • Human classification
    • Kingdom: Animalia (no cell wall, eat other organisms)
    • Phylum: Chordata
    • Class: Mammalia (produce milk from mammary glands)
    • Order: Primates
    • Family: Hominidae
    • Genus: Homo
    • Species: sapiens

Species

  • Most basic unit of biological classification
  • Members of a species are similar (phenotype) to each other but different from other species
    • Similarity can be
      • physical (branching pattern of trees)
      • biochemical (haemoglobin structure)
      • immunological (antibody against an antigen equally effective)
      • development (similar growth of embryos)
      • ecological (occupy identical ecological niche)
  • Members of a species are able to reproduce giving fertile offspring
    • Each species is reproductively isolated from every other species
      • Prevents exchange of genes
      • Species keep special characteristics that distinguishes them

Evidence of classification

  • Biochemical
    • Cytochrome c
      • Protein used in cellular respiration and found in mitochondria
      • Count number of amino acids that organisms differ by
      • Higher number, more distant ancestor
    • DNA hybridisation
      • Unzip DNA from 2 different species
      • Mix them to allow complementary base pairing
      • Higher similarity, more base pairing, more energy required to separate hybrid DNA strands
  • Anatomical
    • Similar anatomical structure, more closely related
  • Embryological
    • Similar stages of development due to common ancestor
  • Immunological
    • Human blood serum is injected into a test animal
    • Test animal recognizes foreign proteins (antigens) and produces antibodies
    • Serum blood of immunized test animal is added to all test tubes
    • Add human serum to one test tube (control)
    • Add serum of other organisms to other test tubes (compare with control)
    • Antigen-antibody complexes form and precipitate from solution
    • Higher amount of precipitation, closer related to humans
  • Behavioural
    • Similar behaviour due to common ancestor
    • Primates live in social groups, communicate by facial expression, long parental care