Diseases

• Communicable diseases are transmitted in different ways:

  • Water (eg. cholera)
  • Air (eg. Erysiphe graminis, fungus causing barley powdery mildew)
  • Contact (eg. TMV)
  • Body fluids (eg. HIV)
  • Animal vectors (eg. malaria)
  • Soil (eg. Agrobacterium tumefaciens)
  • Food (eg. salmonella)
• Pathogens

  • Bacteria
  • Fungi
  • Protists
  • Viruses
• How can we reduced or prevent disease in humans?

  • Being hygienic
  • Destroying vectors
  • Vaccination
  • Isolating infected individuals
• How can we reduce or prevent disease in plants?

  • Destroying infected plants
  • Crop rotation
  • Biological control
  • Chemical control
  • Regulating movement of plant material
• Plants have physical defences against pathogens

  • Waxy cuticle on surface of leaves (waterproof barrier)
  • Cell walls
  • Callose - reinforces cell walls
• Plants have chemical defences against pathogens

  • Plants produce antimicrobial chemicals which kill pathogens or inhibit their growth
  • Plants may be resistant to pathogens due to their genetics.
  • Pyrethrin = Insecticide
  • Cyanide = stops aerobic respiration
  • Citronella = insect repellent
• ELISA test


  1. Antigens on the surface of cells are present in plants affected by a pathogen
  2. In an ELISA test, antibodies are added to the sample being tested, and are then washed off
  3. However, if the antibody binds to the antigen, it remains in the sample
  4. If there is a colour change when the substrate is added, the antigen is present.

  
• Plant diseases - Mosaie Virus

  • Virus
  • Transmitted by tools or other infected plants
  • Symptoms include a yellow mosaic pattern on the leaf, stunted growth and curled leaves
  • Prevent by cleaning tools and killing dead plant
• Plant diseases - Agrobacterium tumefaciens

  • Bacteria
  • Transmitted by contaminated soils and tools
  • Symptoms include round tumour like gals on stems and roots
  • Prevent by disinfecting tools, removing infected plants and not wounding plant
• Plant diseases - Powdery mildew

  • Fungus
  • Transmitted by wind, insects and contaminated surfaces
  • Symptoms include white patches on leaves and early leaf drapping
  • Prevent by improve air circulation, removing infected plants and avoiding excessive humidity.
• Human infections - Chlamydia

  • Bacteria
  • Transmitted through unprotected sex
  • Symptoms include burning feeling when you pee, pain + swelling in Testes, bleeding between periods
  • Treat with antibiotics: 7 - 14 days
• Human infections - Gonorrhoea

  • Bacteria
  • Transmitted through unprotected sex
  • Symptoms include sore testes, discharge from penis or vagina, burning pain when you pee
  • Treat with a single dose of antibiotics
• Human infections - HIV

  • Virus
  • Transmitted through unprotected sex or sharing needles
  • Symptoms include a flu-like illness 2 - 6 weeks after infected
  • The virus damages your immune system, but doesn't show symptoms, therefore can't tell if you are infected
  • Antiretroviral medicines stop it replicating, and the immune system will eventually repair itself
• Human infections - Athlete's foot

  • Fungus
  • Transmitted through wet, warm and humid conditions after being in contact with fungus
  • Symptoms include sore flaky patches on your feet, cracked skin, fluid-filled blisters
  • Treatment available as creams, sprays and powders