Biology Unit 3 Higher Tier covering micro organisms

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Food and Microorganisms

Theory of Biogenesis- Living things are created from other living organisms. There were three scientists who tried to prove this and the most successful was Louis Pasteur.

"The Swan Neck Flask" proved the theory of biogenesis as the bacteria settled in the swan neck showing that it was not the air that cause microorganisms to go off.


  • Bacteria is added to milk
  • Bacteria produces solid curds int he milk
  • Curds are then separated from the whey

Yoghurt (Should learn this properly)

  • Milk is often heated( a method of sterilisation) to kill unwanted micro organisms
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  • Bacteria is then added and this ferments (breaks down glucose by anaerobic respiration) to lactic acid.
  • Lactic acid causes milk to clot and solidify into yoghurt


  • Yeast can respire both anaerobically and aerobically. When yeast breaks down anaeroibally it produces ethanol and carbon dioxide and this carbon dioxide can make bread rise as it expands and gets trapped in the dough.


  • Beer is made from barley grains. These grains are left to germinate where the starch in the grains is broken down into glucose by enzymes. Then they are dried in a kiln which is called malting.
  • Water is added to produce a sugary solution and then this sugary soluted is fermented using yeast to produce ethanol (alcohol).


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Micro organisms in Industry

Micro organisms can be grown in fermenters on a large scale. A fermenter contains a culture medium.

  • Food is provided to the culture medium and air is also pumped in as oxygen is needed.
  • Micro organisms also need to be kept at the right temperature. Micro organisms are constantly producing heat from aerobic respiration therefore a water jacket is placed around the fermenter to cool the temperature.
  • A motorised stirrer keeps the micro organisms from sinking to the bottom and stirring maintains a constant temperature.


  • This is protein from fungi called Fusarium. It is used to make alternatives such as Qourn.
  • This fungus is grown in fermenters and uses glucose for food supply and this comes from digesting starch with enzymes (carbohydrase).
  • This fungus respires aerobically so oxygen is supplied.
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