Classification and evolution

• Taxonomy is the practice of biological classification

  
• Biological classification system


  Enables us to arrange species into groups based on their evolutionary origins and relationships

  
• Taxon


  A group in the hierarchical classification system (plural taxa)
• Grouping organisms into taxa can make them easier to understand and remember
• Taxonomic ranks


  • Species
  • Genus
  • Family
  • Order
  • Class
  • Phylum
  • Kingdom
  • Domain

  
• Hierarchical classification system


  • The higher ranks contain more organisms with less similarity between them
  • The lower ranks contain fewer organisms with more similarity between them

  
• Eukarya is the domain of all eukaryotes, distinguishable from Bacteria and Archaea which are both prokaryotic domains

  
• The classification system is organised within the Eukarya domain

  
• Organisms in the Eukarya domain


  • Wolf
  • Hibiscus rosa-sinensis
• The name of a species always consists of two words: the genus and species
• Binomial


  The scientific name given to an individual species, consisting of the genus and species name in modern Latin
• Binomials are extremely useful for scientists as they allow for species to be universally identified
• The binomial for a species is always typed in italics or underlined when handwritten
• Prokaryotic cells


  Cells that lack a nucleus
• Eukaryotic cells


  Cells that have compartmentalised structures, with at least their genetic material segregated from the rest of the cell in a nucleus
• The three domains of life


  • Bacteria (prokaryotes)
  • Archaea (prokaryotes)
  • Eukarya (eukaryotes)

  
• Archaea


  • Organisms sometimes referred to as the extremophile prokaryotes
  • Archael cells have no nucleus
  • Unique lipids in cell membranes
  • No peptidoglycan in cell walls
  • Ribosomal structure more similar to eukaryotes than bacteria
  • DNA transcription more similar to eukaryotes
• Bacteria


  • Organisms with prokaryotic cells containing no nucleus
  • Vary in size over a wide range
  • Divide by binary fission
• Eukarya


  • Organisms with eukaryotic cells with nuclei and membrane-bound organelles
  • Vary massively in size
  • Can reproduce sexually or asexually
• Key differences between archaea and bacteria


  • Membrane lipids
  • Ribosomal RNA
  • Cell wall composition
• Organisms from the Bacteria domain have cells that always possess cell walls with peptidoglycan
• Organisms from the Archaea domain have cells that always possess cell walls, but these do not contain peptidoglycan
• The five kingdoms (before the three domains)


  • Prokaryota
  • Protoctista
  • Fungi
  • Plantae
  • Animalia

  
• Prokaryota kingdom


  • Includes bacteria and blue-green bacteria
  • Unicellular or form colonies
  • Cells have cell walls and cytoplasm but no nucleus or mitochondria
  • Cells divide by binary fission
  • Some are autotrophic, others are heterotrophic
• Protoctista kingdom


  • Eukaryotic organisms that do not belong to the other three eukaryotic kingdoms
  • Show great diversity in structure, life cycle, feeding
  • Can exist as single-celled or groups of similar cells
  • Protozoa have animal-like cells, algae have plant-like cells

  
• Fungi kingdom


  • Eukaryotic cells
  • Possess non-cellulose cell walls (often chitin)
  • No cilia
  • Heterotrophic, obtain energy and carbon by digesting dead/decaying matter or parasitizing living organisms
  • Reproduce using spores
  • Simple body form, can be unicellular or filamentous hyphae
• Animal cells


  Have no cell wall
• Protoctista (algae)


  • Possess cells similar to plant cells
  • Have cellulose cell walls and chloroplasts
• Protoctist cells


  • Two examples
• Kingdom Fungi


  All fungi are eukaryotic cells
• Fungal cells


  • Possess non-cellulose cell walls (often made of the polysaccharide chitin)
  • Don't have cilia
• Fungi


  • Heterotrophs: use organic compounds made by other organisms as their source of energy and molecules for metabolism
  • Obtain this energy and carbon by digesting dead/decaying matter extracellularly or from being parasites on living organisms
• Fungal reproduction


  Reproduce using spores that disperse onto the ground nearby
• Fungal body form


  • Can be unicellular (like the common baker's yeast Saccharomyces cerevisiae)
  • Some consist of long threads called hyphae that grow from the main fungus body and form a network of filaments called the mycelium
  • Larger fungi possess fruiting bodies that release large numbers of spores (this is how many fungi reproduce)
• Fungus


  • The mould found on bread is actually a fungus: Rhizopus nigricans
• The structure of a fungus with its hyphae, mycelium and fruiting bodies
• Plant cells


  • All have cell walls composed of cellulose
  • Possess large (and usually permanent) vacuoles that provide structural support
  • Are able to differentiate into specialized cells to form tissues and organs
  • Possess chloroplasts that enable photosynthesis (not all plant cells have chloroplasts)
  • Can sometimes have flagella
• Plants


  Autotrophs: can synthesize their organic compounds and molecules for energy use and building biomass from inorganic compounds
• Plant body form


  • Have branching systems above and below the ground
• A typical plant cell