GCSE AQA Biology 1 Fighting Disease

Nota:

• Microorganisms that enter the body and cause disease

1. Bacteria
   1. Very small living cells
   2. Can reproduce rapidly
   3. Can make you feel ill by: damaging your cells & producing toxins
2. Viruses
   1. NOT cells - much smaller
   2. Replicate by invading body cells, using cells' machinery to produce many copies, burst cell - releasing new viruses
      1. Cell damage makes you feel ill

1. Skin, hairs & mucus in respiratory tract stop microorganisms entering
2. Platelets - help blood clot to seal wounds
3. Immune system - white blood cells have 3 ways of attacking microbe...
   1. Consuming them
      1. Can engulf & digest foreign cells
   2. Producing antibodies
      1. When WBC come across foreign antigen (unique molecules on its surface), start producing specific antibodies (proteins) to lock onto & kill cell
         1. Antibodies produced rapidly, if infected with same pathogen WBC will know how to kill it - person is naturally immune
   3. Producing antitoxins
      1. Counteract toxins produced by bacteria

1. Protects from future infections
   1. Vaccinations - injecting small amounts of dead/inactive microorganisms

      Nota:

      • Carry antigens - causing body to attack even though it's harmless
      1. If live microbes appear, WBC can rapidly produce antibodies needed
   2. Some 'wear off' - need booster injections
2. Pros
   1. Have helped control many infectious diseases that were once common
   2. Epidemics can be prevented if large % of population is vaccinated
3. Cons
   1. Don't always work
   2. Can have bad reaction - very rare

1. Painkillers
   1. Only reduce symptoms
2. Antibiotics
   1. Actually kill bacteria
   2. Don't destroy viruses - reproduce using own body cells

1. Bacteria can mutate to develop resistance
   1. When infection is treated, only non-resistant strains are killed
      1. Resistant bacteria will survive and reproduce - population of resistant strain will increase (natural selection)
2. Resistant strain ('superbugs') could cause serious infection that can't be treated by antibiotics e.g. MRSA
   1. Drug companies working on developing new antibiotics
3. To slow down rate of development: doctors must avoid over-prescribing antibiotics - only for serious infections

Nota:

• Testing the action of antibiotics/disinfectants by growing cultures of microorganisms

1. Grown in a 'culture medium' - agar jelly (contains carbs, minerals, proteins and vitamins) in a Petri dish
   1. Inoculating loops used to transfer microorganisms to jelly
      1. Paper discs soaked in antibiotics & placed on jelly - non-resistant strains will die
      2. Must be sterilised (as well as Petri dish & culture medium) - passed through flame to prevent unwanted microbes affecting result
   2. Petri dish lid must be taped on - stop contamination
2. In lab at school - kept at 25 degrees C (harmful pathogens won't grow)

Nota:

• Ignaz Semmelweis - worked in Vienna hospital in 1840s

1. Believed doctors were spreading disease on their unwashed hands
   1. Told them to wash hands in antiseptic solution
      1. Killed bacteria - he didn't know that (wasn't discovered for many yrs) & methods were dropped when he left
         1. Now we know basic hygiene is essential in controlling disease

1. Viruses
   1. Tend to mutate often - difficult to develop vaccines (different antigens)
   2. Could evolve to become deadly & very infectious
      1. Precautions could be taken to stop spread, vaccine & antiviral drugs could be developed
         1. Pandemic could kill many people
2. Bacteria
   1. Can mutate to produce resistant strains
   2. New strain could appear - no one would be immune
      1. Could spread rapidly - epidemic