Infection and Response

• Communicable disease


  A disease caused by a pathogen which can be passed between animals or plants e.g. flu
• Pathogen


  A disease-causing microorganism e.g. bacteria
• How bacteria cause disease

  Once inside the body, they divide rapidly by binary fission. They kill cells and produce harmful toxins.
• How viruses cause disease

  They invade and reproduce inside living body cells, leading to cell damage.
• Ways pathogens can be spread

  • By air - flu, tuberculosis and the common cold are spread by droplet infection
  • By water - fungal spores in water spread plant diseases
  • By direct contact - common in plant diseases and sexually transmitted infections
• Ways to reduce the spread of pathogens

  • Hygiene - handwashing, disinfectants, tissues
  • Reducing contact with infected individuals - quarantine
  • Removing vectors - use of pesticides and insecticides, removal of habitats
  • Vaccination
• Scientists have not yet developed cures for many viral diseases, so it is especially important to prevent the spread of viral diseases
• Measles


  A serious viral disease that can cause blindness and brain damage. The main symptoms are a fever and a red skin rash.
• How measles is spread

  By air - through the inhalation of droplets from coughs and sneezes.
• HIV/AIDS


  HIV is a virus which attacks and damages the immune system until it can no longer function properly. AIDS is the condition resulting from a long-term HIV infection. There is no cure or vaccine for HIV/AIDS.
• Monoclonal antibodies (mAbs)


  Antibodies that are clones from one parent cell, specific to one type of antigen
• How HIV is spread

  Direct sexual contact and the exchange of bodily fluids e.g. blood, breastmilk.
• Ways to prevent the spread of HIV/AIDS

  • Use of condoms
  • Screening of blood for transfusions
  • Not sharing needles
  • Bottle-feeding by HIV-positive mothers
  • Use of antiretroviral drugs to prevent the development of AIDS
• Production of monoclonal antibodies

  1. Specific antigen injected into an animal

  2. B-lymphocytes producing complementary antibodies extracted

  3. B-lymphocytes fused with myeloma cells to form hybridoma cells

  4. Hybridoma cells cultured

  5. Monoclonal antibodies collected and purified
• Tobacco mosaic virus (TMV)


  A plant pathogen which causes leaf discolouration when cells are damaged. Affected areas cannot photosynthesise, reducing the crop yield. As there is no treatment, farmers grow TMV-resistant crop strains to avoid infection.
• Uses of monoclonal antibodies


  • Detection of pathogens
  • Location of cancer cells and blood clots
  • Treatment of cancer
  • Used in pregnancy test kits
• How tobacco mosaic virus is spread

  Contact between infected and healthy plants. Insects may act as vectors which transfer the virus between different plants.
• Salmonella


  A type of bacteria found in raw meat, poultry and eggs. If they enter the body via food poisoning, they can affect natural gut bacteria.
• Myeloma cells


  Type of tumour cell
• Symptoms of salmonella food poisoning

  • Fever
  • Abdominal cramping
  • Vomiting
  • Diarrhoea
• Ways to limit the spread of salmonella

  • Vaccinating animals intended for consumption
  • Keep raw meat away from cooked meat
  • Disinfect hands and surfaces after contact with raw meat
  • Thoroughly cook meat
• Pregnancy kits test for hCG in urine
• Gonorrhoea


  A sexually transmitted bacterial infection caused by unprotected sex with an infected individual. Early symptoms include yellow/green discharge from genitals and painful urination, although it may be symptomless.
• Pregnancy test


  A stick containing monoclonal antibodies (mAbs) specific to hCG: mAbs attached to a blue bead (free to move), mAbs fixed to the test stick
• Rose black spot


  A fungal disease which causes purple or black spots to develop on rose leaves. It reduces the area of the leaf which is available for photosynthesis and causes leaves to turn yellow and drop prematurely.
• How the rose black spot fungus is spread

  Fungal spores are spread by the wind and in water.
• How a pregnancy test works if a woman is pregnant

  1. hCG in urine binds to mAbs attached to a blue bead

  2. mAbs with hCG diffuse up dipstick

  3. mAbs fixed to the stick bind to hCG

  4. Blue line forms
• Aphids


  Use their sharp mouthparts to extract sap from the plant phloem, weakening the plant. They are also vectors who can transfer pathogens from diseased plants to healthy plants.
• How a pregnancy test works if a woman is not pregnant

  No hCG in urine so a blue line is not formed
• Reducing the number of aphids

  1. Chemical pesticides

  2. Biological pest control - using ladybirds
• Advantages of using monoclonal antibodies to test for pathogens

  • Specific to one particular antigen
  • Very accurate
  • Quick results
• How the rose black spot fungus can be treated

  • Using fungicides
  • Destroying infected leaves
• Nitrate ions


  Required to convert sugars into proteins which are required for the plant to grow. If there is not an adequate supply, the growth of the plant will be stunted.
• Magnesium ions


  Required to synthesise chlorophyll, which absorbs light energy during photosynthesis. If there is not an adequate supply, the leaves cannot photosynthesise properly and they turn yellow (chlorosis).
• Tumour markers


  Specific antigens on the membranes of cancer cells
• Symptoms of disease in plants

  • Stunted growth (lack of nitrate ions)
  • Spotted leaves (eg. rose black spot fungus)
  • Decay/rotting
  • Growths
  • Malformation of stems/leaves
  • Discolouration
  • Presence of pests
• Malaria


  Malaria is a disease caused by protist pathogens. The disease is carried from host to host by mosquitoes, and the protists enter the human bloodstream when they feed. Symptoms include fever and shaking, and it may also be fatal in some cases.
• Ways to identify plant disease

  • Reference to a gardening website or manual
  • Laboratory testing
  • Monoclonal antibody test kits
• Ways to reduce the spread of malaria

  • Using insecticides
  • Using insect nets to avoid bites
  • Prevent mosquito breeding by removing stagnant water
  • Antimalarial drugs
• How monoclonal antibodies can be used to diagnose cancer

  1. mAbs tagged to a radioactive substance

  2. mAbs injected into the patient's bloodstream

  3. mAbs bind to 'tumour markers' on cancer cells

  4. Emitted radiation is detected using a specialised scanner enabling doctors to determine the location of cancer cells