AQA A-Level Biology Paper 1, June 2023: Question 5

10 marks · Medium difficulty · Practical Techniques & Data Analysis

Investigate the use of cinnamon oil as an antimicrobial substance using agar plates, aseptic techniques, cylinder volume calculations, and analysis of clear zones.

Practise this question

Question

Question text

05 A student investigated the use of cinnamon oil as an antimicrobial substance.

She investigated the effect of cinnamon oil on the growth of five different bacterial

cultures grown on agar plates.

05.1 The student added 100 mm3 of each bacterial culture from its glass bottle onto a

separate agar plate. She spread each bacterial culture evenly over the agar using a

spreader.

Describe the aseptic techniques she should use.

[3 marks]

05.2 On each agar plate, the student cut a well (a hole) in the agar.

The well had a diameter of 6 mm. The student added 50 mm of cinnamon oil into the

well.

Calculate the minimum depth of the well to allow the addition of 50 mm of cinnamon

oil.

Use the following equation in your calculation:

Volume of a cylinder = πr2 × l

Use 3.14 as the value for π.

Show your working.

[2 marks]

Answer mm

The student kept the plates at 25 °C for 24 hours.

Figure 5 shows what one of her plates looked like after 24 hours.

Figure 5

The student measured the diameter of the clear zone with no bacterial growth around

*13* each well. She made these measurements to the nearest whole mm

Table 1 shows her results.

Table 1

Diameter of clear zone / mm

Bacterial culture

Positive Negative

Cinnamon oil

control control

Bacillus spp. 15 14 0

Staphylococcus aureus 20 17 0

Listeria monocytogenes 18 12 0

Escherichia coli 16 12 0

Klebsiella spp. 14 12 0

Median for all cultures 0

Mean for all cultures 0

Standard deviation for all cultures15 2.4 2.2 0

05.3 Suggest exactly what the student added to the wells to get the positive control and

negative control results.

[2 marks]

05.4 Complete Table 1 to show the median and mean diameters.

[1 mark]

05.5 The mean ± 2 standard deviations includes over 95% of the data.

Use this information to consider whether the standard deviations suggest the

differences in means are likely to be due to chance.

Explain your answer, including at least one calculation.

[2 marks]

Mark scheme

Show the mark scheme

Question Marking Guidance Mark Comments

1. Wash hands with soap

1. Ignore sterilise

hands OR surfaces

1. Accept sanitise for

disinfect

Disinfect surfaces;

1. Accept antiseptic

/antimicrobial/alcohol

2. Use sterile pipette/syringe (to transfer bacteria);

(wipes)

1. and 7 Accept a

3. (Remove bottle lid and) flame neck of bottle;

named type of

disinfectant

4. Lift lid of (agar) plate at an angle;

2. Reject loop

2. Accept use

5. Work close to upward air movement;

unopened pipette/

syringe for sterile

6. Use sterile spreader;

4. Accept lift lid

3 max slightly OR keep lid

7. Place pipette/spreader into disinfectant

05.1 (3 x over plate

(immediately after use);

AO1) 4. Ignore ‘work quickly

with lid off’

5 Reject ‘air

movements sterilise

air’

5 Accept ‘convection

current’ for ‘upward air

movement’

6. Accept loop for

spreader

6. Examples of

sterilising technique

eg, flame OR ‘dip in

alcohol and flame’ OR

‘dip in disinfectant and

rinse (in sterile water)’

Correct answer in range of 1.768 to 1.8 A common correct

answer for 2 marks is

1.77

2 = 2 marks

Accept for 1 mark, evidence of

28/28.26/28.3 (correct calculation, π x 32)

OR 2

05.2 (2 x

28.27433 (correct calculation using π value on

AO3) Accept correct

calculator)

rounding of figures

0.4423 (correct calculation using diameter rather

than radius)

OR 13

1.76 (correct calculation but incorrectly rounded);

(Positive control) If not specified, accept the first

answer as being for the positive

1. Antimicrobial/ antibacterial (solution)

control

1. Accept named

Antibiotic antimicrobial/antibacterial/

2 antibiotic/antiseptic/disinfectant

05.3 (2 x

Antiseptic/disinfectant; AO3)

(Negative control)

2. (Sterile) water

Oil (without cinnamon);

Accept 16.6 and 13.4 as the

Median for all cultures 16 12 mean values (in this order)

05.4

Mean for all cultures 17 13 (AO2)

All four numbers correct;

1. (Mean ± 2SD) 12.2 to 21.8 and 8.6 to

1. Accept ECF for 1 mark,

17.4

correct SDs calculated using

14 OR

incorrect means in 05.4

(Mean ± 2SD) 11.8 to 21.4 and 9(.0) to

17.8

2. Accept ECF for 1 mark,

(Mean ± 1.96 SD) 12.3 to 21.7 and 8.7

correct explanation based on

to 17.3 2

correct SDs calculated from

05.5 (2 x incorrect means in 05.4

AO3)

(Mean ± 1.96 SD) 11.9 to 21.3 and 9.1

to 17.7;

2. (SD) overlap so difference (likely

2. Reject results are due to

to be) due to chance

chance OR results are

significant

(SD) overlap so (likely) no

significant difference (in means);

How to answer it

Investigating the Antimicrobial Properties of Cinnamon Oil

What this question tests

This question assesses your practical competency in microbiology, specifically aseptic techniques, mathematical calculations involving cylinder volumes, experimental controls, descriptive statistics (median and mean), and the evaluation of standard deviations to determine statistical significance.

Question 05.1

Aseptic Techniques for Bacterial Transfer

✅ Correct Marking Points (Max 3)

Wash hands with soap OR disinfect work surfaces.
Use a sterile pipette or syringe to transfer bacteria.
Remove bottle lid and flame the neck of the bottle.
Lift the lid of the agar plate only slightly at an angle.
Work close to an upward air movement (Bunsen burner convection current).
Use a sterile spreader.
Place pipette or spreader into disinfectant immediately after use.

💡 Key Knowledge

Aseptic technique prevents the contamination of bacterial cultures with unwanted microorganisms from the environment, and protects the scientist from pathogenic contamination.

🧠 Exam Technique

Be specific. Examiners reject vague statements like "sterilise equipment" unless you state the method (e.g., flaming or autoclaving) or use pre-sterilised disposable equipment.

❌ Common Errors

Students often lose marks by suggesting an inoculating loop should be flamed when spreading a large volume ( 100 mm³ ) across an agar plate—loops are for streaking or transferring small colonies; spreaders or pipettes must be used here.

Award up to 3 marks from the marking points listed above (3 x AO1).

Question 05.2

Calculating Well Depth

✅ Correct Answer

1.76 to 1.8 mm (Accept 1.77)

📐 Step-by-Step Calculation

Identify the formula: Volume of cylinder = π × r² × l (where l is depth/length).
Rearrange for depth (l): l = Volume ÷ (π × r²)
Convert units / find radius: Diameter = 6 mm, so radius (r) = 3 mm. Volume = 50 mm³.
Substitute values: 50 ÷ (3.14 × 3²) = 50 ÷ (3.14 × 9) = 50 ÷ 28.26
Calculate final value: 1.7692... mm rounds to 1.77 mm (or 1.76 to 1.8).

❌ Common Calculation Traps

Using the diameter (6 mm) directly instead of the radius (3 mm) is the most frequent error. This yields 0.44 mm , which receives 1 mark if clear working is shown.

2 marks total: 1 mark for correct working/formula rearrangement, 1 mark for the correct answer range (2 x AO3).

Question 05.3

Identifying Experimental Controls

✅ Correct Answer

Positive control: An antimicrobial/antibacterial solution, antibiotic, or antiseptic/disinfectant.
Negative control: Sterile water or oil without cinnamon.

💡 Key Knowledge

Controls validate experimental design. A positive control proves the bacteria *can* be killed (verifying test conditions work), while a negative control proves that the carrier substance (water/oil) doesn't inhibit bacterial growth on its own.

🧠 Exam Technique

Make sure you explicitly label which control is which if writing a continuous sentence. If unspecified, examiners mark the first listed substance as the positive control.

2 marks total: 1 mark for positive control substance, 1 mark for negative control substance (2 x AO3).

Question 05.4

Completing Table 1 (Median and Mean)

✅ Correct Table Values

Metric	Cinnamon oil	Positive control
Median for all cultures	16	12
Mean for all cultures	17 (or 16.6)	13 (or 13.4)

🧠 Exam Technique & Working Out

Cinnamon raw data: 15, 20, 18, 16, 14. Ordered: 14, 15, 16, 18, 20. Median = 16. Mean = 85 / 5 = 17.
Positive control raw data: 14, 17, 12, 12, 12. Ordered: 12, 12, 12, 14, 17. Median = 12. Mean = 67 / 5 = 13.4 (Accept whole numbers 17 and 13).

1 mark for all four values correctly calculated and entered (1 x AO2).

Question 05.5

Interpreting Standard Deviations

✅ Correct Answer

The differences in means are likely due to chance because the standard deviations overlap.

📐 Supporting Calculation (Mean ± 2 SD)

Cinnamon oil: Mean = 17, SD = 2.4. Range = 17 ± (2 × 2.4) = 17 ± 4.8 = 12.2 to 21.8
Positive control: Mean = 13, SD = 2.2. Range = 13 ± (2 × 2.2) = 13 ± 4.4 = 8.6 to 17.4
Conclusion: The ranges overlap significantly between 12.2 and 17.4, indicating no statistically significant difference.

❌ Common Errors

Never state that results "are significant" when standard deviations overlap. Overlapping ranges mean variation within samples is too high to rule out chance.

2 marks total: 1 mark for correct calculation of range/SD comparison, 1 mark for concluding that the differences are likely due to chance due to overlap (2 x AO3).

Topics

Practical skills · Required Practicals · Experimental design · Data analysis · AS practicals (1–6)

Question and mark scheme from the AQA A-Level Biology examination, Paper 1, June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.