Microbes

• Spontaneous Generation


  Living organisms arose from non-living objects
• In 1800 many scientists believed that microbes appeared spontaneously (i.e. from nothing!)
• Observations supporting Spontaneous Generation

  • Dead logs were the source of mushrooms
  • Rotting meat was the source of flies
  • Mouldy hay was the source of mice
• Disprove Spontaneous Generation


  Many scientists were sceptical of Spontaneous Generation & set about to understand how organisms came into existence (through the scientific method!)
• People used to believe that flies came from the rotting meat
• Louis Pasteur


  1822-1895, He carried out an experiment to disprove the theory of spontaneous generation of micro-organisms
• Pasteur's Swan-necked flask


  • Allowed air to reach the broth but any particles in the air would be trapped in the S-shaped neck
• Pasteur's experiment


  1. Label the specimen tubes 1-5 and name with your initials

  2. Into tube 1, place some UNBOILED nutrient broth and seal with a solid cork bung

  3. Into tubes 2,3,4 and 5 pour some BOILED broth. Quickly place the correct lid on to each tube
• Apparatus


  • 5 small specimen tubes
  • Piece of straight glass tubing
  • S-shaped glass tubing
  • 4 cork bungs
  • Boiled nutrient broth
  • Unboiled nutrient broth
• Pasteur said "Never will the doctrine of spontaneous generation recover from the mortal blow struck by this simple experiment"
• Pasteurisation


  Heating milk to 72°C for 15 secs kills off any bacteria in the milk