Culturing microorganisms: GCSE Biology
Aseptic technique, incubating cultures, antibiotics practical, binary fission and growth calculations
The short version
Triple Biology cultures bacteria on agar using aseptic technique, then investigates antibiotics and calculates growth by binary fission.
Key idea
Uncontaminated means only the intended microbe is present
Grade 2–3: We grow bacteria in a special jelly dish so we can see them.
Grade 5–6: I can name agar, Petri dish and loop, and say the culture must stay uncontaminated.
Grade 9: I explain that contamination adds unknown microbes (including possible pathogens) so colony counts and antibiotic zones become meaningless.
Go a bit deeper
Examiners buy the order and the reason for each step
Grade 2–3: Keep the lid on as much as you can and do not poke the agar with a dirty loop.
Grade 5–6: I can list: flame, cool, short lid time, cross of tape.
Grade 9: I give a reason for each step, including why full sealing is dangerous (anaerobic pathogens) and why schools do not culture unknown samples.
Worked example
Worked example
Grade 2–3: We grow bacteria in a special jelly dish so we can see them. Grade 5–6: I can name agar, Petri dish and loop, and say the culture must stay uncontaminated. Grade 9: I explain that contamination adds unknown microbes (including possible pathogens) so colony counts and antibiotic zones become meaningless.
Lessons in this topic
- Why we culture microorganisms
- Aseptic technique
- Inoculating and incubating
- Required practical: antibiotics and antiseptics
- Binary fission
- Calculating bacterial growth
In the app each lesson is video (when we have a real YouTube id) then intro, learn and summary steps.
What the examiner wants
Describe aseptic steps, explain 25 °C school incubation, interpret inhibition zones, and calculate bacterial numbers using 2^n after n divisions.
Try these questions
Cover the answers and have a go first. Worked solutions are underneath.
Why are school bacterial cultures incubated at about 25 °C rather than 37 °C?
What is the main aim of aseptic technique?
Why should a Petri dish lid not be taped all the way round?
An inoculating loop is flamed until it glows. What must you do next before picking up bacteria?
Common mistakes
- Do not incubate school cultures at 37 °C. That is body temperature and would encourage pathogens that infect people.
- Flaming then immediately touching the colony kills the bacteria you wanted. Sealing the dish all the way round is a safety dump.
- 25 °C is the school safety temperature, not "the temperature bacteria like best". Hospitals may use 37 °C with proper containment.
- A bigger zone does not prove the antibiotic is safe or that it works inside a person. Do not put the ruler through the agar and contaminate it.
Answers and working
Frequently asked questions
Is GCSE Culturing microorganisms on Combined Science and Triple?
Culturing microorganisms is Triple-only Biology. Combined Science students can skip it.
Which exam board is this Culturing microorganisms page for?
The ideas are board-agnostic for AQA, Edexcel, OCR, WJEC and CCEA. Paper lengths and question numbers differ — check your specification.
Is Culturing microorganisms Foundation or Higher?
The core ideas appear on both tiers. Higher papers add extra application and some HT-only detail, marked in lessons with a Higher badge.
Learn, try, get feedback, fix the mistake
Open the stepped lesson, then the quiz with hints. Required-practical and calculation questions use the same method you will need in the paper.
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