plumiEnzymes: OCR A‑Level Biology A questions
Every OCR A-Level Biology A exam question on 2.1.4 Enzymes, 2016–2025, with its mark scheme and examiner’s report.
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Q17(a)(ii)
The whole paper ↗![June 2025 Paper 1, question 17(a)(ii): The intermediate compound PEP is a reversible non-competitive inhibitor of PFK. Explain how PEP inhibits PFK. [3]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h42001-jun25-17-aii-qp.webp?v=3)
Q17(a)(iii)
The whole paper ↗![June 2025 Paper 1, question 17(a)(iii): ATP is also an inhibitor of PFK. Suggest and explain why ATP cannot be a competitive inhibitor of PFK. [2]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h42001-jun25-17-aiii-qp.webp?v=3)
Q17(a)(iv)
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Q17(a)(v)
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Q17(b)
The whole paper ↗![June 2025 Paper 1, question 17(b): Complete the following sentence. Some inhibitors form strong covalent bonds with enzymes and are known as inhibitors. [1]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h42001-jun25-17-b-qp.webp?v=3)
Q22(b)(ii)
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Q3(a)(i)
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Q3(a)(ii)
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Q3(b)(i)
The whole paper ↗![June 2025 AS Paper 2, question 3(b)(i): Use the graph to calculate the initial rate of the reaction. Give your answer to 2 significant figures. Initial rate of the reaction = cm3 s–1 [3]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h02002-jun25-03-bi-qp.webp?v=3)
Q3(b)(ii)
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Q3(c)
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Q3(d)
The whole paper ↗![June 2025 AS Paper 2, question 3(d): Explain how increasing the substrate concentration affects the enzyme activity. [4]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h02002-jun25-03-d-qp.webp?v=3)
Q16(c)(ii)
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Q21(b)(i)
The whole paper ↗![June 2024 Paper 1, question 21(b)(i): Explain why it is important that catalase is able to break down hydrogen peroxide very quickly. [2]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h42001-jun24-21-bi-qp.webp?v=3)
Q21(b)(ii)
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Q21(c)(i)
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Q21(c)(ii)
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Q25(a)
The whole paper ↗![June 2024 AS Paper 1, question 25(a): Use the graph to calculate the rate of reaction at 50 seconds. Give your answer to 2 significant figures. Rate = cm3 s–1 [2]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h02001-jun24-25-a-qp.webp?v=3)
Q25(b)
The whole paper ↗![June 2024 AS Paper 1, question 25(b): Hydroxylamine inhibits catalase. Describe how the student could show that hydroxylamine is a competitive inhibitor. [2]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h02001-jun24-25-b-qp.webp?v=3)
All 105 questions on Enzymes, as a list
- June 2025, Paper 1, Q3 (1 mark): Which statement about the function of enzymes is not correct? A Enzymes affect the structure of whole organisms. B Enzymes build larger molecules from smaller m
- June 2025, Paper 1, Q17(a)(ii) (3 marks): The intermediate compound PEP is a reversible non-competitive inhibitor of PFK. Explain how PEP inhibits PFK. [3]
- June 2025, Paper 1, Q17(a)(iii) (2 marks): ATP is also an inhibitor of PFK. Suggest and explain why ATP cannot be a competitive inhibitor of PFK. [2]
- June 2025, Paper 1, Q17(a)(iv) (1 mark): Inhibition of PFK by ATP and PEP is an example of a negative feedback control mechanism. State the name of this type of inhibition in metabolic pathways such as
- June 2025, Paper 1, Q17(a)(v) (2 marks): ATP is converted to ADP and then AMP (adenosine monophosphate) when ATP provides energy for processes in the cell. AMP reverses the inhibition of PFK by ATP. Us
- June 2025, Paper 1, Q17(b) (1 mark): Complete the following sentence. Some inhibitors form strong covalent bonds with enzymes and are known as inhibitors. [1]
- June 2025, AS Paper 1, Q22(b)(ii) (2 marks): Drugs that affect DNA replication are used to treat cancer. Zelpolib is a drug that affects the enzyme DNA polymerase by binding to its active site. Suggest exp
- June 2025, AS Paper 2, Q3(a)(i) (2 marks): Enzymes can be used to extract proteins from plant cells. These proteins can be used for food products. The diagram shows how the enzyme pectinase can be used t
- June 2025, AS Paper 2, Q3(a)(ii) (6 marks): (ii)* The table shows some data on different methods that can be used to extract plant proteins. Protein source Extraction method Percentage yield of protein ex
- June 2025, AS Paper 2, Q3(b)(i) (3 marks): Use the graph to calculate the initial rate of the reaction. Give your answer to 2 significant figures. Initial rate of the reaction = cm3 s–1 [3]
- June 2025, AS Paper 2, Q3(b)(ii) (1 mark): The student repeats this experiment at 30 °C and finds the initial rate of reaction to be 4.34 cm3 s–1. Calculate the Q10 for catalase. Give your answer to 2 si
- June 2025, AS Paper 2, Q3(c) (2 marks): The student completes a different experiment to investigate the effect of pH on enzyme action. Suggest how they would vary and detect the pH in their experiment
- June 2025, AS Paper 2, Q3(d) (4 marks): Explain how increasing the substrate concentration affects the enzyme activity. [4]
- June 2024, Paper 1, Q16(c)(ii) (1 mark): The enzyme maltase converts maltose to glucose during the final stages of starch digestion in the small intestine. Suggest why maltotriose can also be converted
- June 2024, Paper 1, Q21(b)(i) (2 marks): Explain why it is important that catalase is able to break down hydrogen peroxide very quickly. [2]
- June 2024, Paper 1, Q21(b)(ii) (3 marks): Fig. 21.1 is a graph of decomposition of hydrogen peroxide against time for catalase. Fig. 21.1 250 200 Hydrogen peroxide 150 decomposed (μg) 100 50 0 0 10 20 3
- June 2024, Paper 1, Q21(c)(i) (2 marks): Superoxide dismutase (SOD) is an enzyme that is often located together with catalase in cells. Superoxide ions are produced in mitochondria and are highly react
- June 2024, Paper 1, Q21(c)(ii) (3 marks): Scientists investigate the effect of hydrogen peroxide on sperm cells. This is the method that they use: • incubate sperm cells with different concentrations of
- June 2024, AS Paper 1, Q25(a) (2 marks): Use the graph to calculate the rate of reaction at 50 seconds. Give your answer to 2 significant figures. Rate = cm3 s–1 [2]
- June 2024, AS Paper 1, Q25(b) (2 marks): Hydroxylamine inhibits catalase. Describe how the student could show that hydroxylamine is a competitive inhibitor. [2]
- June 2023, Paper 1, Q5 (1 mark): Increasing the pH of an enzyme solution from 7.4 to 8.0 causes the rate of the reaction to fall by 90%. When the pH of the solution returns to 7.4 the rate of r
- June 2023, Paper 2, Q15 (1 mark): The image below shows an enzyme and its substrate. Enzyme Substrate Which option represents a coenzyme for this enzyme? A B C D [1] Your answer
- June 2023, Paper 2, Q17(a)(i) (1 mark): State the independent variable in this investigation. [1]
- June 2023, Paper 2, Q17(a)(ii) (2 marks): Describe how a student could produce an 8 a.u. solution from a 20 a.u. stock solution. [2]
- June 2023, Paper 2, Q17(a)(iii) (2 marks): Liver tissue contains a higher concentration of catalase than potato. Suggest two reasons why the students chose potato rather than liver as a source of catalas
- June 2023, Paper 2, Q17(a)(iv) (1 mark): The potato cylinders were cut to equal lengths. Suggest a further precaution the students should have taken when preparing them, to ensure the investigation was
- June 2023, Paper 2, Q17(b)(i) (2 marks): Some of the students’ results are shown in the tables below. Results for 2 a.u. hydrogen peroxide Volume of oxygen produced (cm3) Time Standard (s) 1 2 3 Mean d
- June 2023, Paper 2, Q17(b)(ii) (2 marks): Use the standard deviations to discuss the repeatability of the students’ results. [2]
- June 2023, Paper 2, Q17(b)(iii) (2 marks): The students calculated the initial rate of reaction over the first 30 s. Calculate the rate of reaction over the first 30 s for the result at 2 a.u. hydrogen p
- June 2023, Paper 2, Q17(b)(iv) (2 marks): When analysing the results, the students assumed that the volume of oxygen collected was the same as the volume of oxygen produced from breakdown of hydrogen pe
- June 2023, Paper 2, Q17(c) (3 marks): Fig. 17.2 shows a graph of the students’ results. Fig. 17.2 100 Key: 2 a.u. 8 a.u. 80 20 a.u. 60 Volume of oxygen produced 40 (cm3) 20 0 0 30 60 90 120 150 180
- June 2023, Paper 3, Q2(d)(i) (2 marks): Vitamin C acts as a coenzyme for several enzymes in the synthesis of collagen. Outline the role of coenzymes in biological reactions. [2]
- June 2023, Paper 3, Q2(d)(ii) (2 marks): A scientist investigates the effect of vitamin C on the activity of the enzyme adenylyl cyclase. Adenylyl cyclase catalyses the conversion of ATP to cAMP. The s
- June 2023, AS Paper 1, Q17 (1 mark): Which row in the table shows the different types of variables in the student’s investigation? Control variable Dependent variable Independent variable Volume of
- June 2023, AS Paper 1, Q18 (1 mark): The student determines catalase activity by calculating the rate of oxygen production. Which units of measurement are appropriate to show the rate of oxygen pro
- June 2023, AS Paper 1, Q22(a)(i) (1 mark): Name the hypothesis of enzyme action that is supported by the mechanism observed in chitinase. [1]
- June 2023, AS Paper 1, Q22(a)(ii) (2 marks): Explain how the mechanism of enzyme action observed in chitinase increases the rate of chitin breakdown. [2]
- June 2023, AS Paper 1, Q22(b)(i) (2 marks): The student uses a volumetric flask to measure 250 cm3 of the solution. The volumetric flask has an absolute uncertainty of ±0.12 cm3. Calculate the percentage
- June 2023, AS Paper 1, Q22(b)(ii) (2 marks): Using a pipette, the student transfers several 5 cm3 samples of the plant extract solution during their investigation. The diagram shows three different pipette
- June 2023, AS Paper 1, Q27(a)(i) (2 marks): Suggest how the activity of TET enzymes affects metabolism at both the cellular and whole organism level. [2]
- June 2023, AS Paper 1, Q27(a)(ii) (1 mark): Vitamin C binds to TET enzymes and increases their catalytic activity. State the role of vitamin C when it binds to a TET enzyme. [1]
- June 2023, AS Paper 1, Q27(a)(iii) (1 mark): Intracellular and extracellular reactions are catalysed by enzymes. The table lists three enzymes, including TET. Complete the table to indicate whether the enz
- June 2022, Paper 1, Q4 (1 mark): The graph below shows the effect of changing substrate concentration on the rate of an enzyme- controlled reaction. Rate of reaction Substrate concentration Whi
- June 2022, Paper 1, Q5 (1 mark): Which statement about the effect of temperature on enzyme-controlled reactions is not correct? A At temperatures above 40 °C the rate of all enzyme-controlled r
- June 2022, Paper 1, Q20(b)(i) (2 marks): Calculate the Q10 for respiration in the largest fish. Give your answer to 3 significant figures. Q10 = [2]
- June 2022, Paper 2, Q1 (1 mark): Many processes in the body are controlled by enzymes. Which of the options is an extracellular process controlled by enzymes? A Conversion of fibrinogen to fibr
- June 2022, AS Paper 1, Q2 (1 mark): The reaction between carbon dioxide and water forms carbonic acid. This reaction is catalysed by the enzyme carbonic anhydrase. To catalyse this reaction, carbo
- June 2022, AS Paper 1, Q7 (1 mark): A student carried out an investigation to see the effect of changing the concentration of the enzyme maltase. They used two different maltase concentrations (co
- June 2022, AS Paper 1, Q11 (1 mark): The temperature coefficient (Q10) for catalase is recorded in a data book as 1.15. A student carries out an experiment to test if this Q10 value is correct and
- November 2021, Paper 1, Q4 (1 mark): Which of the statements about enzyme catalysed reactions is true? A Binding of a substrate to the active site can weaken bonds in the substrate. B Enzymes allow
- November 2021, Paper 1, Q5 (1 mark): The figure shows the metabolic pathways leading to synthesis of five amino acids: aspartate, lysine, methionine, threonine and isoleucine. E1 to E8 represent di
- November 2021, Paper 1, Q18(b) (3 marks): Liver is a rich source of the enzyme catalase. The table below describes examples of three terms from the list below. coenzyme competitive inhibition enzyme-pro
- November 2021, Paper 1, Q18(c) (1 mark): Fig. 18.2 shows the effect of concentration of hydrogen peroxide on the rate of reaction of catalase. rate of reaction of catalase (cm3 O2 min–1) concentration
- November 2021, AS Paper 2, Q3(a)(i) (2 marks): Describe how they would create four different enzyme concentrations using tenfold serial dilutions. They started by using a syringe to transfer 1 cm3 of the 1%
- November 2021, AS Paper 2, Q3(a)(ii) (1 mark): State the concentration of trypsin in tube 4 once the tenfold serial dilutions had been completed. Concentration = % [1]
- November 2021, AS Paper 2, Q3(b) (1 mark): Trypsin is an example of a protease enzyme found in the small intestine of mammals. Explain why trypsin is described as an extracellular enzyme. [1]
- November 2021, AS Paper 2, Q3(c) (2 marks): Fig. 3.1 shows how the rate of reaction of trypsin changes with pH. Rate of enzyme reaction 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH Fig. 3.1 With reference to Fig.
- November 2021, AS Paper 2, Q3(d)(i) (2 marks): Other factors may affect the rate of the reaction. Name one other factor they would need to control and describe how they would control this. Factor How they wo
- November 2021, AS Paper 2, Q3(d)(ii) (2 marks): Describe how you would use the apparatus shown in Fig. 3.2 to obtain the results shown in Table 3. [2]
- November 2021, AS Paper 2, Q3(d)(iii) (3 marks): Plot a graph of the results shown in Table 3 on the grid below. [3]
- November 2021, AS Paper 2, Q3(d)(iv) (3 marks): Use your graph to calculate the initial rate of reaction. Give your answer to 2 significant figures. Rate of reaction = cm3 s–1 [3]
- November 2021, AS Paper 2, Q3(d)(v) (1 mark): The students investigating 30 °C calculated the initial rate of reaction to be 0.48 cm3 s–1. Calculate the temperature coefficient (Q10) for this reaction. Give
- November 2021, AS Paper 2, Q3(e) (6 marks): Students carried out a practical investigation into the effect of enzyme concentration on the rate of reaction. They were provided with: • a 1% solution of the
- November 2021, AS Paper 2, Q4(a) (3 marks): Mosquito nets help to prevent the spread of malaria. They are often treated with an insecticide called permethrin. Some mosquitoes have developed resistance to
- November 2020, Paper 2, Q11 (1 mark): Which of the following, A to D, is true of a competitive enzyme inhibitor? A binds to a site other than the active site B changes the shape of the active site C
- November 2020, Paper 2, Q17(b)(i) (2 marks): Calculate how many times more active immobilised tannase is compared to free tannase at pH8.0. Give your answer to an appropriate number of significant figures.
- November 2020, Paper 2, Q17(b)(ii) (1 mark): Draw a line of best fit for the free tannase on the graph. .... Answer on the graph • [1]
- November 2020, Paper 2, Q17(b)(iii) (3 marks): A student concluded that the optimum pH for this tannase enzyme is pH5.8. Explain why the data in the graph might not support the student's conclusion. [3]
- November 2020, Paper 2, Q17(b)(iv) (2 marks): values than free tannase. Suggest why immobilised tannase is more active at pH8 than free tannase. [2]
- November 2020, Paper 3, Q2(c) (1 mark): Creatine kinase (CK) is an enzyme that catalyses reactions in heart muscle. High levels of CK in the blood indicate that a person may have had a heart attack. S
- November 2020, AS Paper 1, Q14 (1 mark): The graph below shows how the rate of reaction of the enzyme pepsin changes with temperature. 0.04 0.03 rate of reaction (s–1) 0.02 0.01 0 0 10 20 30 40 50 temp
- November 2020, AS Paper 1, Q25(b)(iii) (2 marks): Explain why enzymes are essential to all organisms. [2]
- June 2019, Paper 2, Q15 (1 mark): The image below shows a diagram of an enzyme. allosteric site active site Which of the following could be a competitive inhibitor of this enzyme? A B C D Your a
- June 2019, Paper 3, Q3(b) (2 marks): One example of a cold-tolerant molecule present in icefish is a modified form of the protease enzyme trypsin. Fig. 3 shows how trypsin is converted from a molec
- June 2019, Paper 3, Q3(c)(i) (4 marks): Suggest and explain two improvements that would increase the validity of the students’ investigation. Improvement Explanation Improvement Explanation [4]
- June 2019, Paper 3, Q3(c)(ii) (1 mark): Suggest appropriate units to use to represent the rate of enzyme activity in this investigation. [1]
- June 2019, Paper 3, Q3(c)(iii) (2 marks): The students recorded the temperature that produced the fastest reaction rate in each of the five replicates. These results are shown in Table 3. Temperature th
- June 2019, Paper 3, Q3(c)(iv) (2 marks): The students wanted to know whether there was a difference between the reaction rates of the two forms of trypsin at 30 °C. They performed a statistical test on
- June 2019, AS Paper 1, Q7 (1 mark): The diagram below shows the effect of changing substrate concentration on the rate of an enzyme- controlled reaction. rate of reaction substrate concentration W
- June 2019, AS Paper 1, Q8 (1 mark): Which of the following ions, A to D, is required for the hydrolysis of starch by an enzyme? Cl – A K+ B Na+ C Zn2+ D Your answer [1]
- June 2019, AS Paper 1, Q25(c)(i) (2 marks): Explain why there is a difference in the shapes of the curves at 37 °C and 60 °C. [2]
- June 2019, AS Paper 1, Q25(c)(ii) (2 marks): Explain why there is a difference in the shapes of the curves at 25 °C and 37 °C. [2]
- June 2018, Paper 1, Q5 (1 mark): The following graph shows the rate of reaction of an enzyme in different substrate concentrations. A B rate of C reaction D substrate concentration Which letter
- June 2018, Paper 1, Q18(c) (1 mark): Cellulose cannot be digested by animals. Some mammals have bacteria in their stomachs that produce enzymes that can digest cellulose. Explain whether the action
- June 2018, Paper 2, Q3 (1 mark): Celery contains the enzyme catalase, which breaks down hydrogen peroxide into oxygen and water. A student added liquidised celery to a solution of hydrogen pero
- June 2018, AS Paper 1, Q10 (1 mark): A scientist was investigating the effect of two different temperatures on the rate of enzyme controlled decomposition of ammonia, in soil bacteria. They repeate
- June 2018, AS Paper 2, Q4(b)(i) (2 marks): Describe how a non-competitive inhibitor works to inhibit the activity of an enzyme. [2]
- June 2018, AS Paper 2, Q4(b)(ii) (2 marks): Catalase is found in all living things that are exposed to oxygen. It protects cells from oxidative damage by breaking down hydrogen peroxide to water and oxyge
- June 2018, AS Paper 2, Q4(b)(iii) (2 marks): What can the students conclude from their results? [2]
- June 2018, AS Paper 2, Q4(b)(iv) (3 marks): Three rivers in the Himalayan foothills were polluted with copper, which affected the aquatic wildlife. Scientists were provided with one dead Indian Barb fish,
- June 2017, Paper 3, Q4(b)(i) (4 marks): What can you conclude from Fig. 4 about the molecules or ions that affect the functioning of the nitrogenase enzyme? [4]
- June 2017, AS Paper 1, Q19 (1 mark): What is the correct definition of the term coenzyme? A An inorganic ion that forms the centre of a globular protein. B A molecule that binds to the enzyme, chan
- June 2017, AS Paper 1, Q26(a) (3 marks): State three variables that the student would need to control in order to make the results of this investigation valid. 1 2 3 [3]
- June 2017, AS Paper 1, Q26(b)(i) (1 mark): Describe how the rate of reaction was calculated. [1]
- June 2017, AS Paper 1, Q26(b)(ii) (2 marks): Explain what the standard deviation shows in Table 26. [2]
- June 2017, AS Paper 1, Q26(c) (3 marks): Fig. 26 shows the results plotted on a graph with the standard deviations as error bars. The effect of bromelain concentration on the rate of protein digestion
- June 2016, AS Paper 1, Q3 (1 mark): Some inorganic ions have roles in enzyme-controlled reactions. Which of the rows, A to D, in the table below is correct? Role of ion Prosthetic group for Cofact
- June 2016, AS Paper 2, Q4(a)(ii) (1 mark): The region of yellow staining shown in Fig. 4 includes part of the agar where the fungus had not yet grown. What does this pattern indicate about the action of
- June 2016, AS Paper 2, Q4(b)(i) (1 mark): Why is pH not a controlled variable in this investigation? [1]
- June 2016, AS Paper 2, Q4(b)(ii) (1 mark): Identify one variable that has been controlled in this procedure. [1]
- June 2016, AS Paper 2, Q4(b)(iii) (1 mark): Identify one variable, other than pH, that has not been controlled in this procedure. [1]
- June 2016, AS Paper 2, Q4(b)(iv) (1 mark): The procedure required the solution to be stirred and then drops of solution to be placed on a white spotting tile. Suggest why this procedure was followed rath
- June 2016, AS Paper 2, Q4(b)(v) (1 mark): What can be concluded from the results in Table 4.1 about the optimum temperature for lipase activity? [1]
- June 2016, AS Paper 2, Q4(b)(vi) (4 marks): Describe two different ways in which the procedure could be modified to obtain a more accurate value for the optimum temperature for lipase activity. 1 2 [4]
- June 2016, AS Paper 2, Q4(c) (6 marks): (c)* There are two models for the mechanism of enzyme action. Outline how changes in temperature can affect these mechanisms of lipase action. [6]
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