Flashcards · Biology · Culturing Microorganisms and Developing Medicines
Aseptic Technique and Culturing Microorganisms
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What does aseptic mean?
Free from contamination by unwanted microorganisms.
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What does an autoclave do?
Uses steam under pressure, at about 121 °C, to make equipment and medium sterile.
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Why use an autoclave and not boiling?
It reaches a higher temperature, which kills bacterial spores too.
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What is agar?
A jelly made from seaweed, which sets to give a solid medium.
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What does a culture medium contain?
Carbohydrates, proteins or amino acids, minerals and vitamins.
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How is an inoculating loop sterilised?
By heating it in a Bunsen flame until it is red hot.
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Why is the loop cooled before use?
A hot loop would kill the microorganisms being transferred.
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Why is the neck of the bottle flamed?
The flame makes air move outwards, which stops microorganisms falling in.
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Why is the lid taped but not sealed fully?
To let oxygen in, so that anaerobic pathogens do not grow.
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Why are dishes stored upside down?
So that condensation drips onto the lid, not the agar.
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Why is 25 °C used in schools?
Most human pathogens grow best at 37 °C, so there is less risk at 25 °C.
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At what temperature are cultures incubated in industry?
About 37 °C, for faster growth.
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How are used dishes disposed of?
They are autoclaved, with the lid still on.
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Give two reasons for aseptic technique.
To stop contamination of the culture, and to protect people from pathogens.
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How often can bacteria divide?
As often as every 20 minutes in good conditions.
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Common mistake about the lid?
Sealing the dish completely. Tape is used in short strips, so that air can get in.