Question 1
Unit 4 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanWhy are agar plates incubated upside down in a school laboratory?
- Condensation collects in the lid and cannot drip on to the agar
- It gives the bacteria more oxygen
- It stops the agar drying out
- It kills any contaminating fungi
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Question 2
Unit 4 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanA student prepares a plate of bacteria using aseptic technique. Explain two precautions that should be taken, giving a reason for each.
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Question 3
Unit 4 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanA broth culture of yeast was diluted using a serial dilution, 1 cm³ into 9 cm³ each time. 0.1 cm³ of the tube diluted to 10⁻³ was spread on agar. After incubation 74 colonies grew. Calculate the number of colony-forming units per cm³ in the original culture. Give your answer in standard form.
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Question 4
Unit 4 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanCompare and contrast dilution plating with turbidity measurement as methods of finding the growth of a bacterial population.
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Question 5
Unit 4 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanIn which phase of the growth curve of bacteria in a closed culture is the rate of cell division equal to the rate of cell death?
- Lag phase
- Exponential phase
- Stationary phase
- Death phase
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Question 6
Unit 4 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanBacteria were grown in a closed culture of nutrient broth at 37 °C. The table shows the number of living bacteria per cm³ as log₁₀ values. (a) Name the phase from 0 to 2 hours and give one reason why the number of bacteria does not increase. (2) (b) Calculate the exponential growth rate constant between 4 and 8 hours. (3) (c) Explain the shape of the curve between 10 and 14 hours. (2)
| Time / h | log₁₀ living bacteria per cm³ |
|---|---|
| 0 | 3.0 |
| 2 | 3.0 |
| 4 | 3.6 |
| 6 | 4.8 |
| 8 | 6.0 |
| 10 | 7.0 |
| 12 | 7.0 |
| 14 | 7.0 |
| 16 | 6.4 |
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Question 7
Unit 6 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanPlan an investigation into the effect of temperature on the rate of growth of baker's yeast in a liquid culture. Include the control of two variables and the safe and ethical use of the yeast.
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Question 8
Unit 6 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanIn core practical 13 a student measured the absorbance of yeast cultures every hour. Explain why a sample of sterile broth was used in the colorimeter, and why the culture was swirled before each sample was removed.