Microorganisms and Disease

• Microorganism

  A living organism which is so small that it can only be seen with a microscope
• Types of microorganism


  • Viruses
  • Bacteria
  • Fungi
  • Protists
• Fungi are the odd one out as they are not microorganisms
• Pathogens


  Microorganisms that cause disease
• Protist


  An organism belonging to the Kingdom Protista, which consists of just one cell, which is eukaryotic (contains a nucleus)
• Bacterial cell


  • One-celled organism
  • Cell structure different from animal and plant cells
• Cell wall


  Made of a substance called peptidoglycan, not cellulose
• Cell membrane


  Surrounds the cell
• Viruses


  Tiny infectious agents that can only reproduce inside the living cells of other organisms
• Growing microorganisms


  1. Grow on agar in a Petri dish

  2. Bacteria grow into circular patches called colonies

  3. Colonies can be counted to determine original number of bacteria
• Bacterial population growth


  • Dependent on temperature
  • Grows quickly at warm temperatures
  • Slower at low temperatures
  • Killed at very high temperatures
• Freezing food does not kill bacteria, it just stops them growing
• Plant cell wall


  Different from bacterial cell wall
• Virus cell coat

  Made of protein
• Food keeps longer in a freezer than in a refrigerator because the colder temperature virtually stops bacterial growth
• Immune system

  • Provides two lines of defence: preventing entry of pathogens, then killing them inside the body
• Antigen

  A molecule recognised by the immune system as foreign
• Antibody


  A chemical produced by lymphocytes in response to an antigen
• Immune system response


  1. White blood cells detect antigens

  2. Phagocytes attack

  3. Lymphocytes develop specific antibodies

  4. Antibodies destroy microorganisms or mark them for phagocytes
• Memory cells


  Able to produce the correct antibody instantly if the pathogen gets into the body again
• Vaccination


  Introducing weakened or dead pathogens to stimulate the immune system to produce antibodies and memory cells
• Vaccines have to be given before you encounter the real pathogen
• Vaccines can have side effects like aching and inflammation
• Superbugs


  Bacteria that have evolved resistance to many antibiotics
• Preventing MRSA infections


  1. Screen patients entering hospital

  2. Strict hygiene for hospital staff

  3. Visitors recommended to wash hands
• Slowing evolution of antibiotic resistance

  1. Doctors avoid prescribing antibiotics where possible

  2. Doctors vary type of antibiotic used