OCR · A-Level · Biology
Course version: H420 · Version from Sept 2025
(i) use of microbiological aseptic techniques, including the use of agar…
Full specification wording
Use of apparatus and techniques: (i) use of microbiological aseptic techniques, including the use of agar plates and broth
This clause requires you to know and apply aseptic technique when working with microorganisms in both agar plates and broth.
Checked against the OCR H420 specification (opens in a new tab) on .
- Point 11 of 14
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
This clause requires you to know and apply aseptic technique when working with microorganisms in both agar plates and broth. Aseptic technique keeps cultures pure and protects the worker and environment. Key actions: sterilise loops by flaming to red heat and allow cooling; flame the neck of bottles and tubes; lift lids rather than removing them fully; work close to a Bunsen flame with upward air currents; never place loops or lids on the bench; seal and incubate plates inverted at a suitable temperature; autoclave waste. For broth, flame the neck before and after transfer and keep the vessel angled. The distinction between agar plates (solid surface for colonies) and broth (liquid for suspension growth) matters when selecting the correct procedure.
What earns the marks
- Flaming the inoculating loop to red heat and allowing it to cool before use.
- Flaming the neck of bottles or tubes before and after transferring microorganisms.
- Lifting rather than fully removing lids, and never placing them on the bench.
- Working near an upward air current from a Bunsen flame to reduce contamination.
- Incubating agar plates inverted and sealing them appropriately, and treating broth cultures with equivalent aseptic handling.
- Sterilising or autoclaving equipment and waste to prevent contamination and release.
Common mistakes and how to put them right
Using a loop straight from the flame without cooling.
Put it right: Allow it to cool so heat does not kill the inoculum.
Removing a lid completely and setting it down.
Put it right: Lift the lid and hold it, minimising exposure to airborne contaminants.
Treating broth and agar identically without flaming necks.
Put it right: Flame the neck of the vessel during transfers in both cases.
Exam tips
- Look for the option that reduces airborne contamination, such as working near an upward air current.
- Reject options that involve placing equipment or lids on the bench.
- Check whether the option suits agar plates or broth, since the procedures differ in detail.
Try the lesson
The start of the Use of apparatus and techniques: (i) use of microbiological aseptic techniques, including the use of agar plates and broth lesson, made from checked teaching notes for this specification point.
Have a go first
Before transferring bacteria to an agar plate, why is the wire loop passed through a blue flame?
Listen
This clause requires you to know and apply aseptic technique when working with microorganisms in both agar plates and broth. Aseptic technique keeps cultures pure and protects the worker and environment. Key actions: sterilise loops by flaming to red heat and allow cooling; flame the neck of bottles and tubes; lift lids rather than removing them fully; work close to a Bunsen flame with upward air currents; never place loops or lids on the bench; seal and incubate plates inverted at a suitable temperature; autoclave waste. For broth, flame the neck before and after transfer and keep the vessel angled. The distinction between agar plates (solid surface for colonies) and broth (liquid for suspension growth) matters when selecting the correct procedure. A strong answer earns marks for these points. Flaming the inoculating loop to red heat and allowing it to cool before use. Flaming the neck of bottles or tubes before and after transferring microorganisms. Lifting rather than fully removing lids, and never placing them on the bench. Working near an upward air current from a Bunsen flame to reduce contamination. A common slip: Using a loop straight from the flame without cooling. Instead, allow it to cool so heat does not kill the inoculum. Exam tip: Look for the option that reduces airborne contamination, such as working near an upward air current.
Key words
Say what each word means before you turn the card.
Maintaining pure cultures
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Preventing contamination from air and surfaces
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Protecting the worker and environment
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Matching technique to agar plates versus broth
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See every definition
- Maintaining pure cultures
- Aseptic technique keeps cultures pure when working with microorganisms in both agar plates and broth.
- Preventing contamination from air and surfaces
- Working close to a Bunsen flame with upward air currents and lifting lids rather than removing them fully reduces contamination.
- Protecting the worker and environment
- Aseptic technique protects the worker and environment, and waste is autoclaved to prevent contamination and release.
- Matching technique to agar plates versus broth
- Agar plates provide a solid surface for colonies while broth is liquid for suspension growth, so the correct procedure differs in detail.
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