topic 3

• Pathogens are microorganisms that cause infectious disease
• Communicable diseases are infectious so they can be spread between animals and plants
• 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
• Non-specific human defense systems

  • Hair and mucus in nose
  • Stomach acid
  • Skin as physical barrier
  • Cilia and mucus in lungs
• Phagocytosis by white blood cells

  1. White blood cell moves towards pathogen

  2. Engulfs or ingests pathogen

  3. Digests pathogen
• Antibody production by white blood cells

  1. White blood cells produce antibodies

  2. Antibodies attach to antigens on pathogen surface

  3. Help to destroy and kill pathogen
• Antitoxin production by white blood cells

  1. White blood cells produce antitoxins

  2. Antitoxins counteract toxins produced by pathogens
• Vaccination


  • Injection of dead or weakened pathogens
  • Stimulates white blood cells to produce antibodies
  • Memory cells stay in body
  • Antibodies made quickly on reinfection to kill pathogen
• Pathogens and diseases


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


  • Kill bacterial pathogens
  • Specific antibiotics kill specific bacterial pathogens
  • Cannot cure viral diseases
• Painkillers and other medicines

  • Treat symptoms of illness
  • Do not kill pathogens
• Drug discovery and development

  1. Possible drugs selected

  2. Tested for toxicity on cells/tissues/animals

  3. Clinical trials on volunteers for safety and efficacy

  4. Peer review by other scientists
• Monoclonal antibodies


  • Produced from a single clone of cells
  • Specific to one protein antigen
  • Produced using mice
• Uses of monoclonal antibodies


  • Diagnosis (e.g. pregnancy tests)
  • Detecting pathogens or chemicals in labs
  • Identifying molecules in cells/tissues
  • Delivering drugs to target cancer cells
• Plant diseases can be identified by symptoms like spots, discoloration, malformed growth, decay, or presence of pests
• Plant nutrient deficiencies


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

  • Layers of dead cells (e.g. bark)
  • Waxy cuticles on leaves
  • Cellular cell walls
• Plant chemical defense responses

  • Antibacterial chemicals
  • Poisons in plant tissue
  • Thorns and hairs to deter animals