Edexcel IGCSE Biology 复习笔记 1.2.4 Prokaryotic Organisms

Edexcel IGCSE Biology 复习笔记 1.2.4 Prokaryotic Organisms



  • All living organisms can be grouped or ‘classified’ using a classification system that consists of five kingdoms. These five kingdoms are:
    • Animals
    • Plants
    • Fungi
    • Protoctists
    • Prokaryotes


  • The prokaryotes are different from the other four kingdoms (which are all eukaryotes) as prokaryotic organisms are always single-celled and do not contain a nucleus
  • Instead, the nuclear material of prokaryotic cells is found in the cytoplasm
  • Bacteria are prokaryotic organisms





  • Bacteria, which have a wide variety of shapes and sizes, all share the following biological characteristics:
    • They are microscopic single-celled organisms
    • They have a cell wall (not made of cellulose), cell membranecytoplasm and plasmids
    • They lack a nucleus but contain a circular chromosome of DNA
    • They lack mitochondria and other membrane-bound organelles found in eukaryotic cells


  • Examples of bacteria include:
    • Lactobacillus (a rod-shaped bacterium used in the production of yoghurt from milk)
    • Pneumococcus (a spherical bacterium that acts as the pathogen causing pneumonia)


  • Bacteria feed in different ways:
    • Some bacteria can carry out photosynthesis
    • Most feed on other living or dead organisms (if they feed on dead organic matter then they are known as saprobionts or decomposers)



A typical bacterial cell



Prokaryotic Cells Table