disease

• reducing the spread of diseae in plants and farm animals:

  • killing disease-ridden crops
  • general sanitation of indoor areas
  • plant + animals not too close together to prevent transmission
  • pesticides / fungicides
  • chemical dips for animals to step in
  • sterilising farming equipment
  • culling
• culling: killing infected animals
• Athelete's Foot


  pathogen: fungus

  how is it spread?: through contaminated (public) surfaces, skin-to-skin contact [swimming pools, public showers]

  symptoms: flaky and itchy feet

  prevention: anti-fungal cream, wear flip flops.
• Food Poisoning


  pathogen: bacteria

  how is it spread?: uncooked/unwashed meat, unpasteurised milk, raw vegetables and eggs

  symptoms: vomiting, diarrhea, stomach pains, fever

  prevention: wash hands + fruits and veg, check expiration dates.
• HIV / AIDS


  pathogen: viral

  how is it spread?: sexually, sharing needles

  symptoms: weakened immune system

  prevention: no cure, treatment with anti-viral drugs.
• powdery mildew


  pathogen: fungal

  how is it spread?: spread by spores through the wind

  symptoms: white powdery spots on the leaves and stems. leaves fall off. reduces crop yield by 10 - 15%

  prevention: fungicide, killing infected plants.
• TMV


  pathogen: viral

  how is it spread?: contaminated tools, other infected plants

  plants affected: tobacco plants, tomatoes, peppers, orchids

  symptoms: mottled, discoloured leaves

  prevention: remove infected hands, hands + equipment frequently washed.
• crown's gall 


  pathogen: bacterial

  how is it spread?: through a wound in the plant

  symptoms: tumour-like growth encirling the plants stem/trunk, cutting off the sap [sugars] flow = stunted growth

  prevention: infected plants destroyed. don't plants other crops until the bacteria die out due to a lack of host plant.
• Plant Defences

  physical: to prevent entry

  • waxy cuticle
  • (rigid) cellulose cell wall

  chemical: to kill the microoganism

  • antifungal and antibacterials chemical substances released.
• Plant Defences

  insect repellant: to repel the insect vectors that carry disease. e.g. pine resin, citronella from lemon grass
• Plant Defences

  insecticide: to kill insects. e.g pyrethrins made from chrysanthemums
• Plant Defences

  antibacterials: to kill bacteria. e.g. phenols [disrupts the bacterium's cell wall]. defensins [disrupt the cell membrane]
• Plant Defences

  antifungal: to kill fungi. e.g. caffein [toxic to fungi and insects]. chitinases - enzymes that break down the chitin in fungal cell walls.
• Identifying Plant Disease

  • observation - looking for rotten fruit, mottled or discoloured leaves, wilting plants
  • microscopy: electron microscope to see viruses [high resolution and magnification]
• DNA Analysis

  • every plant pathogen has a unique genome.
  • scientist's compare and unknown plant pathogen's genome to a known DNA profile.
  • DNA profiles can be used to identify individual strains of microorganisms.
• Identifying Antigens

  plant pathogens carry specific antigens [proteins[ on their surfaces, which can be identified using chemical analysis.

  scientists have developed diagnostic kits to enable farmers to identify common crop pathogens.
• advantages to DNA analysis: potential to identify a plant pathogen before it causes significant damage to the crop.
• animal defences

  • the skin is the main barrier to infection
  • but if you cut or graze the skin, it means that the pathogens can enter
  • scabs form to prevent pathogens entering and prevent excessive blood loss.
• platelets

  platelets are small fragments of cells made in the bone marrow, they have no nucleus. platelets help blood to clot at the sight of the wound.
• blood clotting + formation of scabs

  1. knife slips causing a deep cut
  2. skin and blood vessels are damaged
  3. platelets stick to the damaged area to form a plug
  4. soluble fibrinogen is changed into insoluble fibrin
  5. fibres of fibrin form a mesh across the wound, trapping blood cells and forming a clot and blood stops leaking.
  6. the clot dries, shrinks, hardens and forms a scab. the skin cells under the scab divide to form a layer of new skin.
• antibodies are proteins produced by lymphocytes
• monoclonal antibodies

  antibodies that are produced in the laboratory from special cells called hybridomas.

  hybridomas are made by fusing together lymphocytes and myelomas (cancer cells)

  each hybridoma produces specific antibodies, which bind to specific target antigens onto the cell surface membrane of specific cells.
• monoclonal antibodies

  1. genetically modified mice are injected with the required antigen, they produce antibodies to that antigen.
  2. the antibody producing cells are collected.
  3. these cells are fused with myeloma cells from the bone marrow to form a hybridoma.
  4. hybridoma cells reproduce, forming clones
  5. the clones produce the required monoclonal antibody, which are then purified and harvested.
• uses of monoclonal antibodies

  1. detecting disease
  2. treating cancers
  3. pregnancy tests
• detecting diseases - use of monoclonal antibodies

  • monoclonal antibodies labelled / dyed with a radioactive element are inserted into patient's blood via a drip.
  • they bind to antigen of diseases cells and act as markers that can be viewed with cameras to identify the location of the disease.
• treating cancers - use of monoclonal antibodies

  • can deliver drugs or radioactive substances directly to cancer cells
  • more effective and minimises damage to surrounding cells.
• pregnancy test- use of monoclonal antibodies

  • a pregnant woman produces a hormone called HCG in her urine.
  • monoclonal antibodies tagged with a (blue) dye bind to the HCG
  • a band of immobile / fixed antibodies on the pregnancy test stick traps them; forming a coloured line.
• pregnancy test- use of monoclonal antibodies

  1. the first section has mobile antibodies complimentary to the hCG hormone - they are also attached to blue beads.
  2. the second section has fixed antibodies complimentary to the hCG hormone. which are stuck to the stick.
  3. the female urinates on the first section , and if hCG is present, it binds to the mobile antibodies attached to the blue beads.
  4. the stationary antibodies then bing to the hCG-antibody complex.
  5. as they are both bound to a blue bead, this results in a blue line.