GCSE Biology Unit 3 - Biogenesis, mico-organisms and their uses & industrial fermentation.

Fairly comprehensive notes on;

  • biogenesis and abiogenesis
  • microbes including bacteria and yeast
  • the uses of these bacteria in activities such as brewing or baking
  • industrial fermentation.

Created for the 2011 AQA unit 3 exam - any changes to the specification since then are not included.

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The Theory of Biogenesis

1. Lazzaro Spallanzani placed meat broth in a tightly sealed jar and boiled the
broth to kill any existing microbes in the jar or broth. He left the jar but found no
growth at all in the next few days.
Conclusion Microbes are found in the…

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Types of MicroOrganisms

1. Bacteria
A bacterium contains cytoplasm, a thin membrane
and occasionally a cell wall. Most bacteria are free
living, NOT parasitic.

2. Yeast
A yeast cell has a nucleus, cytoplasm and membrane
and a cell wall.

3. Moulds
Moulds are structures called hyphae which have
cell walls…

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1.Using Yeast in Baking
Yeast and sugar is added to the flour.
The mixture is left in a warm place.
Carbon dioxide released from the respiration of
the yeast makes the dough rise.
The bubbles of gas expand during baking.
As the bread bakes, any ethanol produced
evaporates off.

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Sterilize inoculating loops
Sterilize petri dishes and culture medium

Content of Growth Medium
The `culture medium' is agar jelly. This is poured liquid onto the petri dish and
sets when cooled. It contains
Mineral ions
Supplements e.g. vitamins, proteins

Industrial Fermenters
a) Medium ­ a food solution containing carbohydrates…

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Mycoprotein, a protein rich food for vegetarians, is made by growing a fungus
Fusarium on starch in aerobic conditions. The biomass is harvested and

Biogas Production

Fuels can be made from the fermentation of natural products, such as biogas.
Biogas is mainly methane, and made from the anaerobic respiration…

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Biogas vs. Gasohol

Advantages Disadvantages
Biogas Renewable Initial cost is high
Reduce combustion of fossil Can take a month to make
fuels eg. coal Storage facilities needed
Reduce air pollution
Clean fuel
Uses organic wastes
Reduces landfill space
Gasoho Renewable Consumption rate is higher
l Reduce combustion of fossil…

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