• Tuberculosis


  Bacterium (mycobacterium tuberculosis)

  
  

  Affects animals

  
  

  Spread directly via droplet infection.

  
  

  Spread indirectly as bacteria can remain in air for long time.
• Bacterial Meningitis


  Bacterium duh (Meningococcal meningitis)

  
  

  Affects humans

  
  

  Spread directly via droplet infection.

  
  

  Spread indirectly as bacteria can remain in air for long time.
• Ring rot


  Bacterium

  
  

  Affects potatoes and tomatoes
• HIV/AIDS


  Virus

  
  

  Affects humans

  
  

  can be directly transmitted through breastfeeding/sex
• Influenza


  Virus

  
  

  Affects animals including humans

  
  

  spread through droplet infection and porr hygiene practises
• Tobacco mosaic virus


  Virus

  
  

  Affects plants
• Black Sigatoka


  Fungus

  
  

  affects banana plants
• Ringworm


  fungus

  
  

  Affects animals including humans
• Athletes foot


  Fungus

  
  

  Affects humans

  
  

  spread via touch
• Potato/tomato blight


  Protoctist

  
  

  Affects potatoes and tomatoes

  
  

  Spread through spores in water
• Malaria


  Protoctist (different species but overall genus name is Plasmodium)

  
  

  Affects animals, including humans.

  
  

  Spread through vectors (mosquitos). Common in hot climates as they are ideal conditions for vectors to breed.
• Direct contact (direct transmission)


  contact of body fluids e.g kissing, sex

  
  

  skin to skin contact

  
  

  microorganisms from faeces transmitted on hands e.g diarrhoeal diseases.
• inoculation (direct transmisssion)


  break in the skin e.g. sex

  
  

  animal bite

  
  

  puncutre wound/sharing needles
• ingestion (direct transmission)


  taking in contaminated food/drink

  
  

  transferring pathogns from hand to mouth.
• Fomites (indirect transmission)


  inanimate objects e.g bedding, socks, cosmetics
• Droplet infection (indirect transmission)


  droplets formed from talking, sneezing and coughing may be infected.

  
  

  Pathogen transferred to healthy person who inhales the droplets.
• Vectors


  transmits communicable diseases from one host to another.

  e.g animals/water
• Factors affecting transmission of communicable diseases (7)

  overcrowding

  
  

  poor nutrition

  
  

  compromised immune system

  
  

  poor waste disposal

  
  

  climate change

  
  

  culture and infrastructure

  
  

  socio-economic factors
• overcrowding


  Healthy people in close quarters with infected person(s). Increased risk of direct and indirect transmission.
• Climate change


  attracts new species of vectors
• Culture and infrastructure


  In many cultures, traditional medical practises can increase transmission.

  
  

  Burial methods can increase transmission
• Socioeconomic factors


  lack of trained health proffessionals

  
  

  insufficient public warning when diseases outbreaks/lack of education e.g safe sex practise

  
  

  lack of medical access

  
  

  Poverty - those who cannot afford treatment can pass pathogens to healthy individuals
• Soil contamination (plants)


  Infected plants leave spores/pathogens in soil which infect next crop

  
  

  Some spores survive the composting process so infection cycle continued when contaminated compost is used.
• transmission in plants - vectors

  wind - pathogens/spores can be carried by the wind and infect healthy crops e.g black sigatoka

  
  

  wind - spores swim on surface film of water on leaves which drop onto plants and infect them.

  
  

  animals - Insects and birds carry pathogens from one plant to another as they feed.

  
  

  Humans - pathogens and spores transmitted by hands/fomites/clothing/transporting crops and plants around the world.
• Factors affecting communicable disease transmission in plants.

  Planting crop varieties that are disease susceptible.

  
  

  overcrowding crops.

  
  

  poor mineral nutrition

  
  

  damp/warm conditions increase survival and spread of pathogens and spores.

  
  

  climate change - increased rainfall/wind promote spread of diseases, changing conditions spread animal vectors to new areas. Drier conditions may reduce disease spread.
• Animal defence against pathogens - skin

  physical barrier - blocks pathogens from entering the body.

  
  

  chemcal barrier - produces antimicrobial chemicals that lower pH, inhibiting pathogen growth.
• Animal defence against pathogens - Mucous membranes


  Protect body openings that are exposed to the environment.

  
  

  Secretes mucous that traps pathogens and contains antimicrobial enzymes.
• Animal defence against pathogens - Blood clotting

  Mesh of protein (fibrin) fibres.

  
  

  plug wounds to prevent pathogen entry and blood loss.

  
  

  Formed by a series of chemical reactions that take place when platelets are exposed to damaged blood vessels.
• Animal defence against pathogens - inflammation


  stimulate swelling, pain, heat and redness.

  
  

  triggered by tissue damage - damged tissue releases histamine which increase the permeability of the blood vessels, so they start to leak fluid in the surroundg area.

  
  

  This causes swelling and helps to isolate any pathogens that may have entered the damaged tissue.

  
  

  Histamine also causes vasodilation (widens blood vessels) which increases blood flow to the affected area. This makes the area hot and brings white blood cells to the area to fight off any pathogens that may be present.
• Animal defence against pathogens - wound repair

  Skin is able to repair itself in case of injury and re-form a barrier against pathogen entry.

  
  

  Surface is repaired by the outer layer of skin cells dividing and migrating to the edges of the wound.

  
  

  Tissue below the wound contracts to bring the edges of the wound closer together. It's repaired using collagen fibres - many collagen fibres form a scar.
• Animal defence against pathogens - expulsive reflexes

  Attempt to expel foreign objects including pathogens from the body. Happens automatically.

  
  

  sneeze occurs when mucous membrane in nostrils are irritated by dust/dirt.

  
  

  cough occurs from irritation of respiratory tract.
• Plant defence against pathogens - waxy cuticle

  Physical barrier

  
  

  Also stops water collecting on the leaf, which ould reduce risk of infection by pathogens that are transferred between plants in water.
• Plant defence against pathogens - cell walls


  Forms physical barrier against pathogens that make it past the waxy cuticle.
• Plant defence against pathogens - callose deposition


  callose is deposited between plant cell walls and plasma membranes during pathogen invasion - makes it harder for pathogens to enter cells.

  
  

  Callose deposition at the plasmodesmata may limit the spread of viruses between cells.
• Plant defence against pathogens - chemical defences

  Some plants produce saponins which destroy cell membranes of fungi and other pathogens.

  
  

  plants also produce chemicals called phytoalexins which inhibit the growth of fungi and other pathogens.

  
  

  Other chemicals produced by plants are toxic to insects which reduces infection as it reduces insect vectors.
• Outline the four main stages in the immune response

  Phagocytes engulf pathogens

  
  

  Phagocytes activate T-lymphocytes

  
  

  T-lymphocytes activate B lympocytes, which divide into plasma cells

  
  

  Plasma cells make more antigens to a specific antigen.
• Immune response stage 1 - Phagocytes engulf pathogens.

  Phagocyte recognises antigens on a pathogen.

  
  

  Cytoplasm engulfs pathogen - may be aided by presence of opsonins.

  
  

  Pathogen now contained in a phagosome in phagocyte's cytoplasm.

  
  

  Lysosome fuses with the phagosome and the enzymes break down the pathogen.

  
  

  Phagocyte presents phagocyte's antigen on cell surface to activate other immunological cells. It acts as an APC.
• Immune response stage 2 - Phagocytes activate T lymphocytes

  Surface of T-lymphocyte covered with receptors which bind to antigens on APC.

  
  

  Each t-lymphocyte has different receptors and they will bind to different complimentary antigens.

  
  

  This activates the T-lymphocytes (clonal selection).

  
  

  T-lymphocytes undergoesclonal expansionand divides to form more T Lymphocytes.
• Types of T-lymphocytes


  T helper cells- activates B-lymphocytes and T-killer cells.

  
  

  T killer cells- Attach and kill virus infected cells.

  
  

  T Regulatory cells- Supresses immune system form other white blood cells - helps to stop immunological cells mistakenly attacking host's body cells.
• Immune response stage 3 - T lymphocytes activate B-lymphocytes, which divide into plasma cells.

  B-Lymphocytes covered in antibodies. Each B cells has different shaped antibody on their surface.

  
  

  Activated when antigen is found to be complementary to their surface antibodies.

  
  

  Also activated by interleukins(sent out by T cells) that bind to their cell surface receptors. (clonal selection).

  
  

  Activated B cells divides into different types of B cells - B-plasma cells and B-memory cells