b3

• Explain why plants infected with tobacco mosaic virus grow slowly.

  discolouration in leaves so less chlorophyll

  reduced photosynthesis

  less glucose produced so less amino acids / proteins / cellulose made
• Explain how the pregnancy test strip works to show a positive result.

  -urine passes through reaction zone

  -HCG hormone binds to the mobile HCG antibody in the reaction zone -passes up the stick

  -HCG hormone binds to the immobilised HCG antibodies in the results zone

  -the other antibodies which do not attach to HCG

  -bind to antibodies in control zone

  -blue dye appears in both control and results zones to show positive result
• How to prevent malaria spread via mosquitoes? 3 ways?

  Method: mosquito net

  Reason: Prevents being bitten

  Method: Vaccination

  Reason: Provides immunity

  Method: Insecticides

  Reason: Kills the mosquitoes
• how is HIV reduced?

  better education into prevention of spread

  condoms more widely available

  better drugs

  more testing
• How do vaccinations prevent viruses?

  • Inactive virus injected into bloodstream
  • white blood cells produce antibodies
  • if infected, white blood cells produce antibodies more quickly
  • These antibodies destroy the virus before it causes major harm
• Monoclonal antibodies

  • inject mouse with antigens
  • collect mouse lymphocytes that make a specific antibody to the antigen
  • lymphocytes are combined with a tumour cell to create a hybridoma
  • hybridoma is cloned to create many cells that produce the antibody
• How does a monoclonal antibody prevent virus infection?

  Monoclonal antibody is specific to the virus antigen

  Monoclonal antibodies attach/ bind to all the virus antigens

  Virus cannot bind to the human cell to enter it's genetic material
• what does the skin do?

  secretes oils and antimicrobial substances that kill pathogens

  covers the body, physically preventing pathogens from entering
• Viruses live and reproduce inside cells, causing cell damage.
• How do bacteria make us ill?

  Produce toxins that damage tissues
• Pathogens are

  microorganisms that cause infectious disease.
• Measles symptoms

  fever

  red-skin rash
• The measles virus is spread by inhalation of droplets from sneezes and coughs.
• HIV is spread by sexual contact or exchange of body fluids
• • HIV initially causes a flu-like illness.
  • Unless successfully controlled with antiretroviral drugs
  • the virus attacks the body’s immune cells.
  • AIDS occurs when the body’s immune system becomes so badly damaged
  • it can no longer deal with other infections or cancers.
• How is salmonella spread


  bacteria ingested in food, or on food prepared in unhygienic conditions.
• Symptoms of salmonella

  Fever

  abdominal cramps

  vomiting

  diarrhoea
• How to control gonorrhoea spread


  treatment with antibiotics

  barrier method of contraception such as a condom.
• What could be treated with penicillin before resistant strains?

  Gonorrhoea
• Gonorrhoea symptoms

  thick yellow / green discharge from the vagina / penis

  pain on urinating
• How is rose black spot spread

  water or wind
• how is rose black spot treated

  fungicides or removing and destroying the affected leaves
• White blood cells help to defend against pathogens by:

  • phagocytosis

  • antibody production

  • antitoxin production.
• nose


  hairs inside it that are coated with mucus, preventing pathogen entry
• trachea and bronchi


  goblet cells secrete mucus trapping pathogens

  cilia hairs sweep the mucus out
• It is difficult to develop drugs that kill viruses without also damaging the body’s tissues.
• • Pre-clinical testing is done in a laboratory using cells, tissues and live animals.
  • Clinical trials use healthy volunteers and patients.

  • Very low doses of the drug are given at the start

  • If safe, further clinical trials to find the optimum dose

  • In double blind trials, some patients are given a placebo.
• uses of monoclonal antibodies

  • for diagnosis such as in pregnancy tests
  • measure the levels of hormones and other chemicals in blood, or to detect pathogens
  • locate / identify specific molecules in a cell / tissue by binding to them with a fluorescent dye
  • to treat some diseases:

  cancer - monoclonal antibody bound to radioactive substance / toxic drug / chemical which stops cells growing and dividing. delivers the substance to the cancer cells without harming other cells in the body.
• Plant diseases can be detected by


  • stunted growth

  • spots on leaves

  • areas of decay

  • growths

  • malformed stems or leaves

  • discolouration

  • the presence of pests.
• how to identify plant diseases


  • reference to a gardening manual or website

  • taking infected plants to a laboratory to identify the pathogen

  • using testing kits that contain monoclonal antibodies.
• stunted growth caused by nitrate deficiency (needed for proteinsynthesis)
• chlorosis caused by a magnesium deficiency
• Physical plant defences


  • Cellulose cell walls.

  • Tough waxy cuticle on leaves.

  • Layers of dead cells around stems (bark on trees) which fall off.
• Chemical plant defences


  • Antibacterial chemicals.

  • Poisons to deter herbivores.
• Mechanical adaptations


  • Thorns and hairs deter animals.

  • Leaves which droop or curl when touched.

  • Mimicry to trick animals.
• 1. phagocyte track downs a pathogen, and then binds to it. 
  2. phagocyte's membrane will then surround the pathogen and engulf it.
  3. enzymes inside the phagocyte break down the pathogen to destroy it
• What do antitoxins do?


  Bind and neutralise the toxins produced by bacteria