Biology Paper 1: Infection & 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
• White blood cell defense against pathogens


  1. Phagocytosis

  2. Antibody production

  3. Antitoxin production
• Vaccination


  Injection of dead or weakened pathogens to stimulate antibody production and memory cells
• 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, do not work on viruses
• Painkillers and other medicines

  Treat symptoms, do not kill pathogens
• Drug development and testing

  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)
  • Laboratory detection of pathogens or chemicals
  • Research to locate molecules
  • Treatment of disease (e.g. cancer)
• Causes of plant disease

  • Spots on leaves
  • Discoloration of leaves
  • Malformed stems/leaves
  • Stunted growth
  • Decay or rot
  • Pest infestations
• Iron, nitrate, and magnesium deficiencies can lead to plant growth problems
• 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 (e.g. berries)
• Plant mechanical defense adaptations


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