Biology 3 Revision Notes:Microbiology

Notes for B3 on Microbiology


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  • Created on: 30-03-12 18:25
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Growing Microbes
The study of microorganisms is called microbiology. These include bacteria, viruses and fungi, all
too small to be seen by the naked eye. Many microorganisms can be grown in a lab, where we can
research them and find out what they need to survive ­ and learn which are useful for us and which
want to kill us.
Learning more about microorganisms requires culturing them (i.e. growing large numbers to see
their behavior as a colony). For this to happen, you must provide them with everything they need: a
culture medium with carbohydrate(s) to act as an energy source, and necessary nutrients (mineral
ions, and sometimes proteins and vitamins ­ included). The nutrients are usually contained in an agar
medium ­ a substance which dissolves in hot water and will set to form a jelly. Hot agar containing
the nutrients is poured into a Petri dish and left to cool before any microorganisms are added.
Warmth and oxygen is usually needed for growth too.
Safety in the Lab
It is essential that all microbe culture is done carefully, even when growing the safe microorganisms.
This is because they can be pathogenic, and the safe ones can mutate to become harmful
pathogens. The other problem is crosscontamination between microorganisms, which can upset
experiments ­ but more importantly is a health and safety issue when they get onto human skin and
you bring them everywhere with you.
Provided with a lot of oxygen, yeast cells will respire aerobically. They break down sugar as an
energy source, producing the waste products carbon dioxide and water. However, sometimes there
is a lack of oxygen, so they respire anaerobically, which produces ethanol and carbon dioxide.
Ethanol is alcohol. And this process of anaerobic respiration in yeast cells is called fermentation.
Like with humans, aerobic respiration is better for the cells because it produces more energy. This
energy allows them to grow and reproduce however, when there are a large number of yeast cells,
they can survive longer without oxygen and so can respire anaerobically, breaking down sugars into
Yeast is used to produce bread and alcoholic drinks. In bread production, the yeast grows and
respires ­ producing carbon dioxide which causes the bread to rise. The gas bubbles expand when

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baked due to the high temperatures, giving the bread its light, wafery texture. All yeast cells are
killed by the heat in the cooking process.
We can make beers and wines using yeast. Making beer relies on the process of malting, where
barley grains are soaked in water to keep them warm. Germination begins and enzymes break
down the starch in the grains into a sugary solution. This solution is extracted and used as an energy
source for the yeast.…read more

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Mass Production of Microbes
We need microbes in large quantities for production of drugs, like antibiotics, and food. To grow
microbes on an industrial scale, large vessels called fermenters are used. These have been
developed to prevent occurrences which stop bacterial growth. They react to changes, to try and
maintain a stable environment (i.e. if external temperature increases, the fermenter will decrease
internal temperature to restore balance). Industrial fermenters usually have:
1.…read more

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Antibiotic Production
In 1928, Alexander Fleming left some bacteria culture he had been growing on some plates near
an open window. When he returned to look at them, microbes had grown, but there were patches
of mould surrounding the agar and bacteria had stopped growing there. Whatever blew in from the
wind had killed the bacteria.…read more

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A flammable mixture of gases, known as biogas, forms when bacteria break down the waste
material of dead animals or plants in anaerobic conditions. The main component is methane,
although the contents varies. The methane content tends to be around 50 to 80 per cent of the gas,
the rest is made of carbon dioxide, water, hydrogen and hydrogen sulphide.…read more

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be extracted by distillation and used as a car fuel. Many cars run on a mixture of petrol and
ethanol, which can prove cheaper than fully petrol.…read more


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