Biology B3 Unit 3

Unit 3.1 - 3.7 

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Further Biology!

Revision Cards for Microbiology - Biology B3 Unit 3.1 - 3.7

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Growing microbes

Microorganisms are grown on agar or in petri dishes - agar contains carbohydrate as an energy source, but may also contain some minerals, protein + vitamins as extra nutrients

Aseptic Technique;

Sterilise the inoculating loop, which is used to transfer microbes to the agar, by heating it to red hot in the flame of the bunsen and then leaving it too cool - the bunsen also provides updraft stopping microbes decent

Dip the loop in bacteria and use it to make zig zags across the surface of the agar and shut the lid as quickly as possible to avoid contamination

Secure the lid of the petri dish with tape to prevent microorganisms from the air contaminating.

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Food production using yeast

Yeast cells have a nucleus, cytoplasm + cell membrane surrounded by a cell wall

When oxygen is present, they respire aerobically and reproduce quickly

If oxygen is absent they respire anaerobically and produce alcohol and carbon dioxide = fermentation

Glucose ---> alcohol + CO2 

When beer is brewed the starch in barley grains is used as the carbohydrate source for the yeast - germinated to release sugar by the action of enzymes on the starch. The sugar becomes the respiratory substrate of the yeast. Hops are added to provide bitter flavour

Wine is made from fruit. The yeast uses the natural sugars in the fruit as an energy source

Spirits are distilled - boiled to 80c and the vapour that comes off is condensed

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Food production using bacteria

Yeast = added to bread, respires to form CO2 which is trapped in bubbles to lighten the loaf

Lacto Bacilli = Milk goes sour if left

Yogurt = A lacto-basiclus culture is added to warm milk. The milk sugar (lactose) is fermented by the bacteria, producing lactic acid. The lactic acid causes the milk to solidify so yogurt is formed

Cheese - Rennet is used to curdle milk. The way is removed and is compressed. A cultured bacteria and fungus (for blue) is added to develop a particular flavour

Quorn = A single celled fungus cultured on a large scale. Quorn is very rich in protein and fibre

Beer = Another fungus culture, although we consume the yeast products rather than the yeast

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Industrial microbe production

Industrial fermenters are large vessels used to grow microorganisms. The conditions in the fermenter are very closely monitored;

  • There is an air supply providing oxygen for respiration.
  • There is a stirrer used to keep the microorganisms spread out to make sure the temperature is the same in all parts of the vessel.
  • There is a water-cooled jacket around the outside, as the respiring microorganisms release heat and a constant temp. 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. Fusarium is grown aerobically on starch.

Microbe growth phases;

lag phase = getting used to conditions exponential phase = increasingly increasing rate of growth

stable = population matches carrying capacity death phase = waste products stop the microbe living

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Antibiotic production

Alexander Fleming identified the potential value of penicillin in 1928

He noticed clear patches on agar plates, where a fungus was killing bacteria in areas

Penicillin is made from the mould penicillium in a fermenter

Penicillium is latch cultured so that at the end of the food supply (sugar and nitrogen) on an agar plate, it produces the penicillin chemical, which is then extracted

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Plants and waste material (containing carbohydrates) can be broken down by microorganisms anaerobically to produce biogas. The gas is mainly methane.

This can be done on a large scale with waste from factories or sewage works

On a small scale it can be used by a home or a farm. The gas produced is a fuel and provides energy. It also leaves organic fertiliser for the farm.

It is normal to warm  biogas generator to get the process going. Once going it is exothermic!

Biogas generators are carbon neutral - carbon dioxide produced is used to re-grow the plants the following year making the process sustainable.

Usually the generators are made of concrete buried in the ground.

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More biofuels

Sugar cane juices and glucose, derived from maize starch by the action of a carbohydrase enzyme, can be fermented to produce ethanol.

Microorganisms respire anaerobically in this process, using sugars as the energy source.

The ethanol produced must be distilled. It can then be used as a fuel in motor vehicles. 

Using ethanol as a fuel could replace fossil fuels in the future. In terms of the 'greenhouse effect' using ethanol as a fuel is much more 'carbon friendly'. 

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Sean Greaves


On the 5th revision card, you didn't mention that some things, like yeast, need to be kept in an air tight environment so they respire anaerobically to produce other products - like ethanol..

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