Infection & Response

• Pathogens are microorganisms that cause infectious disease
• Types of pathogens


  • Bacteria
  • Viruses
  • Fungi
  • Protists
• Bacterial pathogens


  May reproduce quickly in the body and produce toxins that damage tissue
• Viral pathogens


  Infect and reproduce themselves inside body cells
• Human defense systems


  • Nose (hair and mucus)
  • Stomach (hydrochloric acid)
  • Skin (physical barrier)
  • Lungs (cilia and mucus)
• Phagocytosis


  White blood cell moves towards pathogen, engulfs and digests it
• Antibody production


  White blood cells produce antibodies that attach to antigens on pathogens and help kill them
• Antitoxin production


  White blood cells produce antitoxins to counteract toxins produced by pathogens
• Vaccination


  Injecting dead or weakened pathogens to stimulate antibody production and memory cells
• Pathogens and diseases


  • Salmonella (food poisoning)
  • Gonorrhea (sexually transmitted disease)
  • Measles (viral disease)
  • HIV (viral disease)
  • Tobacco mosaic virus (plant disease)
  • Rose black spot (fungal plant disease)
  • Malaria (protist disease)
• Antibiotics


  Kill bacterial pathogens, do not work on viruses
• Painkillers and other medicines

  Treat symptoms of illness, do not kill pathogens
• Drug development


  1. Possible drugs selected

  2. Pre-clinical trials on cells/tissues/animals

  3. Clinical trials on volunteers

  4. Peer review
• Monoclonal antibodies


  Produced from a single clone of cells, specific to one protein antigen
• Uses of monoclonal antibodies


  • Diagnosis (e.g. pregnancy tests)
  • Detecting pathogens or hormone levels in labs
  • Locating molecules in cells/tissues
  • Delivering drugs to target cancer cells
• Plant disease indicators


  • Spots on leaves
  • Discoloration of leaves
  • Malformed stems/leaves
  • Stunted growth
  • Areas of decay or rot
  • Presence of pests
• Plant nutrient deficiencies


  • Iron deficiency
  • Nitrate deficiency
  • Magnesium deficiency
• Plant defense responses


  • Physical (layers of dead cells, waxy cuticles, cell walls)
  • Chemical (antibacterial chemicals, poisons)
  • Mechanical (thorns, hairs, mimicry)