Infection and response

• Communicable diseases

  • Rose black spot
  • Fungal diseases
  • Bacterial diseases
  • Viral diseases
  • Protist diseases
• Pathogens


  • Microorganisms that cause disease
  • Reproduce rapidly
  • Cause symptoms by damaging cells or secreting toxins
• Viruses

  Enter and reproduce inside cells, causing cell death
• Types of communicable diseases

  • Gonorrhoea
  • Salmonella
  • Malaria
  • Measles
  • Tobacco mosaic virus
  • HIV
• Transmission prevention

  1. Improving hygiene

  2. Using contraception

  3. Vaccination

  4. Destruction of infected plants/animals
• Herd immunity

  Protects those unable to receive vaccinations
• Vaccination


  • Contains dead/attenuated version of pathogen
  • Triggers an immune response
  • Memory cells remain - if pathogen re-enters body, it is recognised and destroyed quickly
• Painkillers


  Only treat symptoms
• Antibiotics

  Kill bacteria only
• Difficult to kill viruses without damaging host cells
• Resistance due to overuse of antibiotics
• Non-specific defences

  • Skin
  • Nose
  • Trachea/bronchi
  • Stomach
• Immune response

  • White blood cells produce antibodies, antitoxins, and engulf pathogens in phagocytosis
• Drug development


  Drugs originally made from plants and microorganisms are now synthesised
• New drug development

  1. Preclinical testing

  2. Clinical trials to test for toxicity, efficacy and dose
• Vaccination programmes reduce the spread of disease
• Transmission methods

  • Direct contact
  • Airborne microorganisms
  • Indirect contact (e.g. through infected surfaces)
  • Contaminated food and drink
• Production of monoclonal antibodies

  1. Mouse lymphocytes are stimulated to produce a particular antibody

  2. Lymphocytes are extracted and fused with cancer cells

  3. Forms a hybridoma cell

  4. Selected hybridoma cells are cloned to produce many identical copies

  5. Large quantities of antibodies can be produced

  6. Antibodies are purified
• Monoclonal antibodies


  • Highly specific to one antigen
  • Can target specific cells or chemicals in the body
• Applications of monoclonal antibodies

  • Pregnancy tests
  • Measure the concentration of chemicals in the blood
  • Locate substances in cells or tissues using a fluorescent dye
  • Cancer treatment - targets cancer cells only
• Monoclonal antibodies bound to

  • Radioactive substance
  • Toxin
  • Drugs
• Pathogens detected by monoclonal antibodies

  • HIV, AIDS
• Monoclonal antibodies are expensive to produce
• Monoclonal antibodies can have unwanted side effects
• Detecting disease


  Studying symptoms can identify the disease without the need for tests
• Symptoms


  • Abnormal or stunted growth, rot, discolouration, spots on leaves, visible signs of pathogens (e.g. bacterial slime/eggs)
• Causes of disease


  • Nutrient deficiencies
  • Viral, bacterial or fungal pathogens
  • Insects, e.g aphids
• Nutrient deficiencies


  • Nitrate deficiency = stunted growth (nitrates used in protein synthesis)
  • Magnesium deficiency = chlorosis (magnesium needed to make chlorophyll)
• Viral, bacterial or fungal pathogens

  E.g tobacco mosaic virus, black spot (fungal)
• Methods of identifying disease

  • Bark/dead cells around stem
  • Test in lab
  • Monoclonal antibody test kits
  • Use gardening manual/website
• Plant defences


  • Chemical
  • Mechanical
  • Physical
• Chemical defences

  • Poisons
  • Antibacterial chemicals
• Mechanical defences

  • Cellulose cell walls
  • Thorns and hairs
• Physical defences

  • Waxy cuticle
  • Mimicry