Biology GCSE (1)

B3 Chapter 3

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  • Created on: 21-12-10 20:34

Growing microbes

microorgnanisms are grown on agar in petri dishes

Agar contains carbohydrate as an energy source, and some minerals, proteins and vitamins as extra nutrients

to make a microorgnaism:

1. sterilise the inoculating loop with a Bunsen burner

2.  dip the loop in a suspension of the bacteria you want to grow and drag zig zags across the agar.

3. close the lid quickly to get rid of any unwanted microbes


These should be incubated at 25 degrees. If grown at higher temperatures harmful microorganisms are more likely to grow.

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Food production using yeast

yeast is a single celled organism with a nucleus, cytoplasm and cell membrane surrounded by a cell wall

oxygen present - yeast respires aerobically and reproduces quickly

oxygen absent - yeast respires anaerobically and produces alcohol (ethanol) and carbon dioxide. This is called fermentation.


Beer - when brewed the starch in the barley grains is used as the carbohydrate energy source for the yeast.

The starch is broken down into sugars by enzymes during germinating process.

When the sugars have been fermented, hops are added to give beer the flavour.


Wine - the grapes contain 'natural' sugars which the yeast uses as an energy source.

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Food production using bacteria

Bacteria is used to produce cheese and yoghurt.



1. bacteria added to warm milk

2. milk sugar (lactose) is fermented by bacteria producing lactic acid

3. lactic acid causes the milk to soldify (clot) and yoghurt is formed.

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Large scale microbe production

industrial fermenters are large vessels used to grow microorganisms

in the fementer:

there is an air supple providing oxygen for respiration

there is a stirrer used to keep the microorganisms spread out and to make sure the temperature is the same throughout the vessel

there is a water cooler jacket around the outside as the repsiring microorganisms release heat and a constant temperature needs to be maintained.

there are sensors to monitor pH and temperature


the fungus Fusarium is grown to produce mycoprotein ()a protein rich food suitable for vegetarians). It is grown aerobically on starch

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Antibiotic production

Penicillin is ade from the mould penicillium in a fermenter

The solution inside the vessel (medium) contains sugar for energy and some other nutrients including nitrogen. Penicillium only starts to produce the antibiotic when most of the nutrients are used up.

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Biogas is mainly methane

it is made by the anaerobic fermentation of a wide range of waste substances and plant material containing carbohydrate.

the gas is produced by fermentation. The microorganisms respire anaerobically to produce the gas.

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ethanol can be produced by fermenting sugar cane juices and glucose derived from maize starch from a carbohydrase enzyme. Micro-organisms respire anaerobically in this process.

the ethanol produced must be distilled before it can be used as a fuel in vehicles.


sugar cane --> ethanol

maize --> starch broken down to sugars using enzymes --> ethanol

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