AQA · Biology · 8461
GCSE Biology: Culturing microorganisms
Cell biology · AQA GCSE Biology (8461), specification point 4.1.1.6. Cards are generated from the exam board's own specification for "Culturing microorganisms", and every card links back to the page it came from. Separate science only. Specification © AQA — used with attribution.
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What is the name of the simple cell division by which bacteria multiply?
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Binary fission.
How often can bacteria divide under ideal conditions?
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As often as once every 20 minutes, given enough nutrients and a suitable temperature.
Bacteria can be grown in a nutrient broth solution or as colonies on an ? gel plate.
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agar
Why are uncontaminated cultures of microorganisms needed?
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To investigate the action of disinfectants and antibiotics — contaminants would make the results unreliable.
Starting from one bacterium dividing every 20 minutes, how many bacteria are there after 2 hours?
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64. Two hours = 6 divisions, so 2⁶ = 64.
Why must Petri dishes and culture media be sterilised before use?
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To kill any unwanted microorganisms that would otherwise contaminate the culture.
How is an inoculating loop sterilised before transferring microorganisms?
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By passing it through a flame, which kills any microorganisms on it.
Why is a Petri dish stored upside down during incubation?
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To stop condensation dripping onto the agar surface and disturbing the colonies.
Why is the lid of a Petri dish secured with adhesive tape?
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To stop microorganisms from the air entering and contaminating the culture.
At what temperature should bacterial cultures be incubated in school laboratories?
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25°C.
Why are school cultures incubated at 25°C rather than 37°C?
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To reduce the risk of growing pathogens harmful to humans, which thrive at body temperature (37°C).
Which formula gives the cross-sectional area of a bacterial colony or clear zone?
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Area = πr², where r is the radius of the circle.
What is measured on agar plates to compare the effect of different antibiotics on bacteria?
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The zone of inhibition — the clear area around each disc where bacteria have not grown.
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