A blank nine-step write-up with the correct table headings. Print it for a real lesson and fill it in by hand. See the specimen lab book
Blank write-up: Microbiology
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Study Hack Lab
RP 2 · Biology
Microbiology
Write-up template
Name
Date
Course
GCSE Biology
Board and specification
AQA GCSE Biology (8461), 4.1.1.6Apparatus and techniques: AT 1, AT 3, AT 4, AT 8
Class and teacher
Aim
Compare how well three antiseptics stop bacteria growing, by measuring the clear zone round a disc of each on an agar plate of E. coli.
Contents
Plan and risk assessment
Apparatus
Method
Results
Graph
Analysis
Conclusion and evaluation
Make safe and clear up
A blank write-up for use in a real lesson. The headings follow the AQA required practical; the readings are yours to take. Layout v1, practical v3. Original material; not affiliated with AQA, which has not reviewed it.
1 Plan and risk assessment
Each antiseptic diffuses out of its paper disc into the agar, getting weaker as it spreads. Visible bacterial growth is inhibited where the antiseptic is sufficiently concentrated, so a clear zone (a zone of inhibition) forms round the disc while a cloudy lawn grows everywhere else. Zone size depends on growth inhibition and diffusion through the agar; clear agar alone does not prove that bacteria were killed.
area = π r²
Variables
Independent (you change)
Dependent (you measure)
Control (you keep the same)
Prediction
One disc is soaked in sterile water. What do you expect round it after 48 hours?
Two antiseptics spread through the agar at the same rate, but one stops these bacteria growing even when it is weak. How will its clear zone compare?
Antiseptic cream is thick and does not soak into the agar easily. Compared with the liquid antiseptics, its zone will be…
Risk assessment
Hazard
Harm it could cause
Control
2 Apparatus
Sterile nutrient agar plate The agar is food for the bacteria; the Petri dish keeps them in.
Culture of E. coli (a safe strain made for schools) in a bottle The bacteria you grow as a lawn.
Sterile plastic pipette Moves a few drops of culture onto the agar.
Glass spreader Spreads the culture evenly over the agar.
Small beaker of ethanol, with a lid The spreader is dipped in it, then flamed, to sterilise it.
Bunsen burner on a heatproof mat Sterilises the spreader and forceps; its updraught keeps microbes away from the plate.
Filter-paper discs (6 mm) Each one carries a liquid onto the agar.
Mouthwash, TCP, antiseptic cream and sterile water The antiseptics to compare, and water for the control disc.
Forceps Pick up and place the discs without touching them.
Clear sticky tape Holds the lid on with two short strips.
Wax pencil Labels the base of the plate.
Disinfectant spray and antibacterial hand wash Kills microorganisms on the bench and your hands.
Discard pot of disinfectant Used pipettes, spreader and forceps go in it.
Incubator set to 25 °C Keeps the plate warm for 48 hours so the bacteria grow.
30 cm ruler (resolution 1 mm) Measures each clear zone’s diameter through the base.
Safety goggles Protect your eyes from antiseptic splashes.
3 Method
Write numbered steps someone else could follow. Say what you measure, with which instrument, and how you keep it a fair test.
4 Results
The table is drawn before you measure. Record each reading to the resolution of the instrument, then work out the mean of your repeats, leaving out any anomaly.
Observations after 48 hours at 25 °C
Looking at
Observation
The whole plate
Other colonies
The water (control) disc
Clear zones · Each zone measured through the base, across the centre of the disc: diameter 1 left to right, diameter 2 at right angles. Means to 1 decimal place.
Antiseptic
Diameter 1 in mm
Diameter 2 in mm
Mean diameter in mm
Area of clear zone in mm²
Mouthwash
TCP
Antiseptic cream
Sterile water (control)
Anomalies
Ring any anomalous result. Say what probably went wrong and whether you repeated it.
5 Graph
Bar chart of the areas · Draw a bar chart. Antiseptic goes along the bottom.
6 Analysis
Area: Mouthwash
area = π r² (r = mean diameter ÷ 2)
Answer
Area: TCP
area = π r² (r = mean diameter ÷ 2)
Answer
Area: Antiseptic cream
area = π r² (r = mean diameter ÷ 2)
Answer
How a clear zone forms
Answer
7 Conclusion and evaluation
Conclusion
Conclusion: what do your results show? Use your own numbers.
Sources of error
For each, say whether it is systematic or random, and how it affected your results.
Judging where the edge of each clear zone is
Zones that are not perfectly round
Discs put on dripping with antiseptic
A colony of another microorganism inside a clear zone
Zones running into each other
Measuring from the edge of the paper disc instead of across its centre
Ruler resolution (1 mm) on a small zone
Only one plate
Improvement
How could you improve the method? Say why it would help.
8 Make safe and clear up
Do not open the plate: keep the lid taped on
Put the plate in the autoclave bag for your teacher to sterilise
Put the spreader and forceps in the discard pot of disinfectant