3. Infection and response

• Salmonella - causes food poisoning

  Symptoms - fever, cramps, vomiting, diarrhoea

  Symptoms produced by the toxins produced by bacteria
• Gonorrhoea is an sexually transmitted disease,

  Symptoms - pain when urinating, thick yellow discharge

  Treatments - antibiotics

  Prevention - condoms
• How to prevent the spread of bacteria

  • Being hygienic - washing hands thoroughly
  • Destroying vectors - killing by using insecticides or destroying habitats
  • Isolation - isolating an infected person will prevent the spread
  • Vaccination - people cannot develop the infection and then pass it on
• Fungal - Rose black spot

  This shows black spots on the leaves of a plant. This means less photosynthesis occurs. The plant does not grow as well

  It is spread by wind or water

  Treatments - fungicides and taking leaves off infected plant
• Protists - Malaria is caused by a protist; Mosquito is the vector

  Malaria can cause fever and can be fatal
• Nitrate deficiency causes stunted growth

  Nitrate ions are needed to make amino acids

  Amino acids make proteins

  Protein allows growth
• Magnesium deficiency causes chlorosis (yellow leaves) as they are needed to make chlorophyll
• Detection of plant disease

  • Stunted growth
  • Spots on leaves
  • Areas of decay
  • Discolouration
  • Presence of pests
• Physical plant defences

  • Cellulose cell walls
  • Tough waxy cuticle on leaves
  • Layers of dead cells around stems which fall off
• Chemical plant defences

  • Antibacterial chemicals
  • Poisons to deter herbivores
  • Thorns or hairs to deter animals
  • Leaves that droop or curl when touched
• Identification of a plant disease

  • Refer to gardening manual
  • Take infected plant to a lab
  • Use testing kits that contain monoclonal antibodies
• Human defences - non specific

  1. Nose - nasal hairs, sticky mucus and cilia prevent pathogens entering the nostrils
  2. Trachea - lined with mucus to trap dust and pathogens. Cilia move the mucus upwards to be swallowed
  3. Stomach acid - kills most ingested pathogens
  4. Skin - hard to penetrate waterproof barrier. Glands secrete oil which kill microbes
• Human defences - specific

  White blood cells

  Phagocytosis is when white blood cells engulf pathogens and digest them
• White blood cells produce antitoxins to neutralise the toxins
• White blood cells produce antibodies.

  Pathogens have antigens on their surface

  Antibodies lock onto the antigen on the outside of the pathogen. WBC can then destroy the pathogens
• Vaccinations protect us from future infections
• Vaccination process

  • Involves and injection of a dead or inactive version of the pathogen
  • They carry antigens which cause the body to produce antibodies which will attack the pathogen
  • If you get infected then the WBC can produce antibodies quickly
• Vaccinations

  Pros - help control communicable diseases, epidemics can be prevented

  Cons - don't always work, some people have a bad reaction to them
• Having a vaccination allows the body to respond faster to an infection
• New drugs need to be tested and trialled to make sure they are safe and effective. These are tested for toxicity, efficacy, and dose.
• Testing dugs process

  1. Studies in the lab
  2. Testing on animal tissue
  3. Small group of healthy people
  4. Large group of healthy people
  5. People that are infected
  6. The drug is released worldwide
• Placebo - looks like the drug but contains no drug
• Double blind trial - neither the scientist or patient knows if they are have been given the drug, or the placebo
• Digitalis came from foxgloves
• Aspirin comes from willow
• Penicillin came from penicillin mould
• Penicillin was discovered by Alexander Fleming
• Antibiotics are medicines that cure bacterial diseases
• Antibiotics cannot be used to kill viruses
• Resistant strains of bacteria have evolved e.eg MRSA - these are not affected by antibiotics
• Painkillers do not kill pathogens, but the treat the symptoms
• Antivirals damage tissues as well as kill the virus
• Herd immunity is when a large proportion of a population is vaccinated, so that the disease cannot spread