Cards (5)

  • Most micro-organisms are harmless and many play an essential role in recycling nutrients in the environment (e.g. nitrogen and carbon cycle). Some can cause diseases (pathogens); others are useful (produce antibodies)
  • A pathogen is a disease causing micro-organisms
    Examples are:
    • Bacteria
    • Viruses
    • Fungi
  • Bacteria
    It is believed that some bacteria are the oldest forms of life
    • A bacteria cell contains cytoplasm, cell membrane and cell wall
    • No nucleus, only a stand of circular DNA
    • Bacteria reproduce by dividing in two or form clones
  • Viruses
    • Viruses are smaller than bacteria
    • They contain a protein coat surrounding a number of genes
    • They can only reproduce in a host cell
    • Producing new viruses destroys the host cell as the new viruses are free to attack other cells
  • Communicable diseases
    This means by which bacteria, viruses and fungi can be spread are as follows:
    • Contact
    • Aerosol
    • Body fluids
    • Water
    • Insects
    • Contaminated food