AQA GCSE B3- Microbiology

All the facts you need to know from the section of Microbiology of Biology Unit 3 at GCSE level. 

  • Created by: Ruqiya
  • Created on: 12-05-11 17:23

Basic, general must know facts for the exam

Microbiology is the study of all things too small to be seen by the eye. This includes bacteria, viruses & fungi. 

To learn about microorganisms we need to CULTURE them.To do this, you have to provide nutrients and an energy source (usually carbohydrates). The nutrients are kept in an agar medium (a substance which dissolves in hot water to form and will set to form a jelly). The agar is set into a Petri dish, and is left to cool before any microorganisms are added.

Oxygen and warmth are required for the microrganisms to grow. 

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Yeast- a single celled organism.

  • Without Oxygen, they respire anaerobically which produces Ethanol and CO2. This is known as  FERMENTATION. 
  • With Oxygen, they respire aerobically. This produces H2O and CO2. This is useful as they break down the sugar as an energy source allowing them to grow and respire.  

Bread production:  The yeast grows + respires, producing CO2 which allows the bread to rise. Due to high temp., the gas bubbles expand when baked causing a wfery, light texture. All yeast cells are killed during the process due to the heat.

Wine production: Uses natural sugar in grapes as energy source. The grape juice is mixed with water and yeast. The yeast respires anaerobically until all the sugar is used up. The yeast is then filtered out, and the juice is bottled and left to mature.  

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Yeast (2)

Beer production: 

1) Malting- Barley grains are soaked in water to keep them warm.

2) Germination begins and enzymes break down the starch in the barely grains into a sugary solution. This solution is extracted and used as an energy source for the yeast. The yeast and sugar mixture is fermented to produce alcohol.

3) Hops are added to give the beer its flavour. It is then left to settle. 

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Food production using other bacteria

Yoghurt: Fermenting only whole milk used to be the only way yoghurt was made, but now any type of milk is used. First, a starter of bacteria is added to warm milk (the milk is warm so the bacteria can grow and reproduce). Next, the bacteria ferments the milk sugar (lactose) producing lactic acid.

The lactic acid causes the milk to clot & solidify into yoghurt. Further bacterial action causes the yoghurt to become creamy. 

Cheese:  Making cheese is fairly similiar to making yoghurt except a different type of bacteria is used. The lactose in mil is still fermented into lactic acid but there is much more produced to the extent that the solid parts (curds) have solidified completely. Enzymes are added so that the milk and the solid parts can be separated after it has been fully curdled

Next, the curds are mixed with different moulds and left to ripen depending on what flavour is wanted. 

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Growing microbes

Microbes are required in large quantites for different reasons such as production of drugs and food. To grow them, large vessels called fermenters are used.

They have:

  • Air supply for Oxygen for respiration of microorganisms.
  • Watercooled jacket to remove heat produced by the respiration.
  • Stirrer to maintain temperature and keep the microorganisms in suspension.
  • Instruments to monitor pH and temperature levels. 
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Mycoprotein and penicillin

The fungi, Fusarium, is used to make mycoprotein (a proten-rich food for vegetarians). The fungus is grown in a large fermenter in aerobic conditions and the biomass is haversted + purified. 

The antibiotic, penicillin, is made by growing the mould Penicillium, in a fermenter. The medium contains sugar and other nutrients eg a source of nitrogen.  The Penicillium only starts to make penicillin after using up most of the nutrients for growth. It was Alexandra Fleming who discovered it.

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Nice notes :)

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