Infection and response

• 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
• 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, efficacy and dose

  3. Pre-clinical trials on cells, tissues or animals

  4. Clinical trials on healthy volunteers and patients

  5. 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
  • Treating disease (e.g. cancer)
• Causes of plant diseases

  • 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 physical defense responses

  • Layers of dead cells around stems
  • Waxy cuticles on leaves
  • Cellular cell walls
• Plant chemical defense responses

  • Antibacterial chemicals
  • Poisons in plant tissue and berries
• Plant mechanical adaptations


  • Thorns
  • Hairs
  • Leaves that droop or curl
  • Mimicry