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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  • Created by: Sarah
  • Created on: 03-01-12 18:29
Preview of GCSE Biology Unit 3 - Biogenesis, mico-organisms and their uses & industrial fermentation.

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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 air.
2. Theodore Schwann demonstrated that all living things come from cells and that
new cells originate from existing cells, forming the basis for biogenesis.
Conclusion Living organisms originate from other living organisms.
3. Louis Pasteur put a broth in a flask, melting and bending the neck of the flask.
This was heated to expel air and kill existing microbes ­ when left there was no
growth. Pasteur repeated the experiment with a normal neck and found that there
was decay.
Conclusion Schwann's theory was correct.
Definitions of the Theories
ABIOGENESIS = the theory that living things can spontaneously come into being
from nonliving matter.
BIOGENESIS = the theory that living things come only from other living things

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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 surrounding cytoplasm and numerous
Yeast can respire aerobically or anaerobically.…read more

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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.
2. Using Yeast in Brewing
Starch in barley is broken down into glucose in malting by
enzymes in germinating grains.
Yeast is added and fermentation occurs.
In beer making, hops are added for flavour.…read more

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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 of plant
products or waste materials ­ as long as they contain carbohydrates.
On a large scale ...…read more

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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 than pure petrol
fuels eg.…read more

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