plumiCulturing microorganisms: OCR A‑Level Biology A questions
OCR A-Level Biology A past-paper questions on 6.2.1.4 Culturing microorganisms, 2016–2025, with mark schemes and examiner’s reports where available.
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All 38 questions on Culturing microorganisms, as a list
- June 2025, Paper 1, Q7 (1 mark): In experiment one, what is the number of cells in the culture after 10 hours? 0.9 × 107 A 4.0 × 107 B C 7.6 7.6 × 107 D Your answer [1]
- June 2025, Paper 1, Q8 (1 mark): Which line, A to D, in experiment two represents a culture where the growth rate is approximately double that in experiment one? Your answer [1]
- June 2025, Paper 2, Q4 (1 mark): Culturing microorganisms on nutrient agar requires aseptic techniques. What is not part of a standard aseptic procedure when culturing microorganisms? A Disinfe
- June 2025, Paper 2, Q5 (1 mark): Batch fermentation with microorganisms is used to produce a range of useful substances. Which of the following are important for achieving maximum yield during
- June 2024, Paper 2, Q12 (1 mark): Aseptic conditions are important when culturing microorganisms. Which option is not a correct part of the procedure for spreading bacteria on an agar-filled Pet
- June 2024, Paper 2, Q13 (1 mark): A standard growth curve for a population of bacteria of the same species in a closed system involves a death phase. Which option explains the death phase? A Int
- June 2024, Paper 3, Q1(b)(i) (2 marks): Describe two improvements to the student’s method, other than using different equipment, that could improve the accuracy of their population estimate. 1 2 [2]
- June 2024, Paper 3, Q1(b)(ii) (3 marks): The student counts 22 colonies on the agar plate. Calculate the total number of E. coli cells in the original 50 cm3 culture. Give your answer in standard form.
- June 2023, Paper 2, Q9 (1 mark): The graph below shows the population of viable bacteria in a flask over 48 hours. B 8 C 7 6 D 5 Number of A bacteria cells 4 (Log) 3 2 1 00 8 16 24 32 40 48 Tim
- June 2022, Paper 2, Q17(a)(i) (1 mark): State why it is important that the technique used for culturing microorganisms be aseptic. [1]
- June 2022, Paper 2, Q17(a)(ii) (2 marks): The students prepared the culture by adding a suspension of bacteria to a flask containing nutrient broth. List two precautions that should be taken when prepar
- June 2022, Paper 2, Q17(b)(i) (1 mark): The students shook each flask before they removed the samples for counting. Suggest why the students shook the flasks. [1]
- June 2022, Paper 2, Q17(b)(ii) (1 mark): It can be more difficult to count bacterial cells using a light microscope than it is to count human cells. Suggest one reason why bacterial cells are difficult
- June 2022, Paper 2, Q17(b)(iii) (3 marks): In one 0.01 cm3 sample the students counted 52 bacterial cells under the microscope. Describe the calculation steps the students would then need to make to esti
- June 2022, Paper 2, Q17(c)(i) (2 marks): Explain, with reference to the graph, why the students used a logarithmic scale on the y-axis. [2]
- June 2022, Paper 2, Q17(c)(ii) (3 marks): Calculate the percentage decrease in the viable population between 40 h and 48 h. Give your answer to 3 significant figures. Percentage decrease = % [3]
- June 2022, Paper 2, Q17(d) (4 marks): Explain, with reference to the graph, the decrease in the population of viable bacteria between 40 h and 48 h. [4]
- June 2022, Paper 2, Q21(c)(i) (1 mark): Use the diagram to name the type of fermentation process used for mycoprotein production. Justify your answer. Name Justification [1]
- June 2022, Paper 2, Q21(c)(ii) (2 marks): Suggest and explain why a cooling system is necessary. [2]
- June 2022, Paper 2, Q21(c)(iii) (2 marks): The air inlet provides the fungus with oxygen for respiration, and ammonia. Suggest and explain why the fungus is provided with ammonia. [2]
- November 2021, Paper 3, Q2(d)(i) (4 marks): A student looked at Fig. 2.3 and made the following statement: ‘The bacterial growth curve in Fig. 2.3 looks very different from a standard growth curve for bac
- November 2021, Paper 3, Q2(d)(ii) (3 marks): Calculate the total number of bacterial cells that would have been present in a 50 cm3 container on day 1. Write your answer in standard form. Number of bacteri
- November 2021, Paper 3, Q2(d)(iii) (2 marks): Describe a laboratory procedure that the scientists might have used to estimate the bacterial population. [2]
- November 2020, Paper 1, Q20(c)(i) (3 marks): Describe how the student could use 1 cm3 pipettes and 10 cm3 measuring cylinders to dilute the sample so that it was 10 000 times less concentrated. [3]
- November 2020, Paper 1, Q20(c)(iii) (2 marks): The student prepared a starter culture using 2.5 × 10−3 g yeast cells in 1 dm3 nutrient broth. The average mass of a yeast cell is 2.0 × 10−11 g. Calculate the
- November 2020, Paper 1, Q20(c)(iv) (3 marks): The population of this yeast doubles every 90 minutes when growing under ideal conditions. A different starter culture was prepared containing 1 × 107 cells. Us
- June 2019, Paper 3, Q6(a)(ii) (3 marks): On an industrial scale, microorganisms can be cultured using either batch fermentation or continuous fermentation. The table below lists statements about indust
- June 2019, Paper 3, Q6(b)(i) (3 marks): Serial dilutions can be used to estimate the size of a bacterial population in a culture. A scientist used 20 cm3 of a bacterial culture that contained 1.0 × 10
- June 2019, Paper 3, Q6(b)(ii) (1 mark): A student carried out a different serial dilution to estimate the size of another bacterial population. The serial dilution resulted in four colonies developing
- June 2018, Paper 2, Q19(a) (1 mark): State one further variable the students should have controlled in their investigation in order to produce valid results. [1]
- June 2018, Paper 2, Q19(b)(i) (2 marks):
- June 2018, Paper 2, Q19(b)(ii) (3 marks): The students disagreed about which tube’s result to use as a starting point for their calculation. Discuss whether the petri dish resulting from Tube F was the
- June 2018, Paper 2, Q19(c)(i) (6 marks): The processed results from the students’ investigation are shown in Table 19.2. Time after Number of viable bacteria Number of viable bacteria incubation presen
- June 2018, Paper 2, Q19(c)(ii) (2 marks): No bacteria were detected at any time in the flask that was inoculated with nutrient broth that did not contain bacteria. Explain the purpose of this flask. [2]
- June 2018, Paper 2, Q19(c)(iii) (1 mark): The teacher told the students they should not investigate the growth of bacteria at 35 °C. Suggest why the teacher told them not to grow bacteria at 35 °C. [1]
- June 2018, Paper 2, Q19(c)(iv) (3 marks): The teacher also suggested that the students should have carried out the investigation using three flasks at each temperature. Explain how this suggestion would
- June 2017, Paper 3, Q2(b)(ii) (2 marks): Describe two practical considerations to ensure the S. cerevisiae population grows successfully when the initial culture is established. [2]
- June 2017, Paper 3, Q2(b)(iii) (2 marks): Scientists wanted to estimate the number of yeast cells in a 25 cm3 solution of S. cerevisiae. They carried out the following two dilutions: • 1 cm3 of the orig
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