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Biological reactions are regulated by enzymes: WJEC A‑Level Biology questions

Every WJEC A-Level Biology exam question on 1.4 Biological reactions are regulated by enzymes, 2016–2025, with its mark scheme and examiner’s report.

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1,223 questions

  1. Q6(c)(ii)

    Summer 2025 · Unit 3

    2 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2025 Unit 3, question 6(c)(ii): TMP is a competitive inhibitor of dihydrofolate reductase, which is an enzyme involved in DNA synthesis. With reference to Image 6.4, explain how compound X mig

  2. Q3(b)(i)

    Summer 2025 · AS Unit 1

    1 mark1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2025 AS Unit 1, question 3(b)(i): The starch phosphorylase solution and the glucose-1-phosphate solution were both placed in the water bath for 5 minutes to equilibrate. Explain why this is impo

  3. Q3(b)(ii)

    Summer 2025 · AS Unit 1

    2 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2025 AS Unit 1, question 3(b)(ii): glucose-1-phosphate to the test tube. The graduated pipette was accurate to ±0.2 cm3. Calculate the percentage error of the volume measured. [2] percentage erro

  4. Q3(b)(iii)

    Summer 2025 · AS Unit 1

    2 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2025 AS Unit 1, question 3(b)(iii): The results of the investigation are shown in Table 3.2. Table 3.2 Time taken for iodine solution to turn blue-black / Mean rate of Concentration minutes starch

  5. Q3(b)(iv)

    Summer 2025 · AS Unit 1

    3 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2025 AS Unit 1, question 3(b)(iv): Describe and explain the effect of glucose-1-phosphate concentration on the mean rate of starch synthesis during this investigation. [3]

  6. Q3(b)(v)

    Summer 2025 · AS Unit 1

    4 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2025 AS Unit 1, question 3(b)(v): One of the limitations of this practical is that the results depend on a subjective judgement of the colour change. State two other limitations and suggest how

  7. Q5(b)

    Summer 2025 · AS Unit 1

    3 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2025 AS Unit 1, question 5(b): The enzyme tyrosinase converts tyrosine into melanin. Explain why only tyrosinase can catalyse this reaction. [3]

  8. Q5(c)

    Summer 2025 · AS Unit 1

    4 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2025 AS Unit 1, question 5(c): Melanin is a pigment that is responsible for dark fur colouration. The more melanin produced the darker the fur. In Siamese cats, the conversion of tyrosine to

  9. Q1(b)(iii)

    Summer 2024 · Unit 3

    2 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2024 Unit 3, question 1(b)(iii): Image 1.4 shows ball and stick models of another Krebs cycle intermediate, succinic acid, and a molecule that is believed to act as a respiratory poison, maloni

  10. Q3(a)

    Summer 2024 · AS Unit 1

    2 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2024 AS Unit 1, question 3(a): Hydrogen peroxide decomposes slowly without catalase. Explain how catalase speeds up the decomposition and suggest why this is so important in living cells. [2]

  11. Q3(b)(i)

    Summer 2024 · AS Unit 1

    2 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2024 AS Unit 1, question 3(b)(i): Some students investigated how the concentration of hydrogen peroxide affected the rate of oxygen production. They used fresh potato puree and different concent

  12. Q3(b)(ii)

    Summer 2024 · AS Unit 1

    4 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2024 AS Unit 1, question 3(b)(ii): Use the data from Table 3.2 to complete Graph 3.3 to show the rate of oxygen production against the concentration of hydrogen peroxide. [4] Graph 3.3 0 0

  13. Q3(b)(iii)

    Summer 2024 · AS Unit 1

    3 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2024 AS Unit 1, question 3(b)(iii): Describe and explain the trend shown in Graph 3.3. [3]

  14. Q3(b)(iv)

    Summer 2024 · AS Unit 1

    2 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2024 AS Unit 1, question 3(b)(iv): Suggest two ways in which the validity of the data could be improved. [2]

  15. Q3(b)(v)

    Summer 2024 · AS Unit 1

    1 mark1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2024 AS Unit 1, question 3(b)(v): Copper sulfate is a non-competitive inhibitor of catalase. On Graph 3.3, draw a labelled line to show how the result would be different if the experiment was re

  16. Q1(a)(iv)

    Summer 2023 · AS Unit 1

    1 mark1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2023 AS Unit 1, question 1(a)(iv): Lysozyme works by an induced fit mechanism. Explain what this means. [1]

  17. Q1(b)(i)

    Summer 2023 · AS Unit 1

    3 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2023 AS Unit 1, question 1(b)(i): Describe and explain the effect of pH on the activity of lysozyme. [3]

  18. Q1(b)(ii)

    Summer 2023 · AS Unit 1

    2 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2023 AS Unit 1, question 1(b)(ii): Lysozyme has a wider range of pH activity than many other enzymes. I. Use Graph 1.3 to find the range of pH over which the activity of lysozyme is more than 50%

  19. Q5(c)(i)

    Summer 2022 · AS Unit 1

    5 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2022 AS Unit 1, question 5(c)(i): Using Graph 5.3 and your own knowledge, compare the relative lactase activity of the free and immobilised lactase at the following temperatures. Expl

  20. Q6(c)

    Summer 2022 · AS Unit 1

    2 marks1.4 Biological reactions are regulated by enzymes
    The whole paper ↗
    Summer 2022 AS Unit 1, question 6(c): Thrombin catalyses the hydrolysis of an arginine-glycine bond in fibrinogen as shown in Image 6.3. Image 6.3 Image 6.4 ARG GLY GLY ARG H2O X ARG GLY Name the ty
All 53 questions on Biological reactions are regulated by enzymes, as a list
  1. Summer 2025, Unit 3, Q6(c)(ii) (2 marks): TMP is a competitive inhibitor of dihydrofolate reductase, which is an enzyme involved in DNA synthesis. With reference to Image 6.4, explain how compound X mig
  2. Summer 2025, AS Unit 1, Q3(b)(i) (1 mark): The starch phosphorylase solution and the glucose-1-phosphate solution were both placed in the water bath for 5 minutes to equilibrate. Explain why this is impo
  3. Summer 2025, AS Unit 1, Q3(b)(ii) (2 marks): glucose-1-phosphate to the test tube. The graduated pipette was accurate to ±0.2 cm3. Calculate the percentage error of the volume measured. [2] percentage erro
  4. Summer 2025, AS Unit 1, Q3(b)(iii) (2 marks): The results of the investigation are shown in Table 3.2. Table 3.2 Time taken for iodine solution to turn blue-black / Mean rate of Concentration minutes starch
  5. Summer 2025, AS Unit 1, Q3(b)(iv) (3 marks): Describe and explain the effect of glucose-1-phosphate concentration on the mean rate of starch synthesis during this investigation. [3]
  6. Summer 2025, AS Unit 1, Q3(b)(v) (4 marks): One of the limitations of this practical is that the results depend on a subjective judgement of the colour change. State two other limitations and suggest how
  7. Summer 2025, AS Unit 1, Q5(b) (3 marks): The enzyme tyrosinase converts tyrosine into melanin. Explain why only tyrosinase can catalyse this reaction. [3]
  8. Summer 2025, AS Unit 1, Q5(c) (4 marks): Melanin is a pigment that is responsible for dark fur colouration. The more melanin produced the darker the fur. In Siamese cats, the conversion of tyrosine to
  9. Summer 2024, Unit 3, Q1(b)(iii) (2 marks): Image 1.4 shows ball and stick models of another Krebs cycle intermediate, succinic acid, and a molecule that is believed to act as a respiratory poison, maloni
  10. Summer 2024, AS Unit 1, Q3(a) (2 marks): Hydrogen peroxide decomposes slowly without catalase. Explain how catalase speeds up the decomposition and suggest why this is so important in living cells. [2]
  11. Summer 2024, AS Unit 1, Q3(b)(i) (2 marks): Some students investigated how the concentration of hydrogen peroxide affected the rate of oxygen production. They used fresh potato puree and different concent
  12. Summer 2024, AS Unit 1, Q3(b)(ii) (4 marks): Use the data from Table 3.2 to complete Graph 3.3 to show the rate of oxygen production against the concentration of hydrogen peroxide. [4] Graph 3.3 0 0
  13. Summer 2024, AS Unit 1, Q3(b)(iii) (3 marks): Describe and explain the trend shown in Graph 3.3. [3]
  14. Summer 2024, AS Unit 1, Q3(b)(iv) (2 marks): Suggest two ways in which the validity of the data could be improved. [2]
  15. Summer 2024, AS Unit 1, Q3(b)(v) (1 mark): Copper sulfate is a non-competitive inhibitor of catalase. On Graph 3.3, draw a labelled line to show how the result would be different if the experiment was re
  16. Summer 2023, AS Unit 1, Q1(a)(iv) (1 mark): Lysozyme works by an induced fit mechanism. Explain what this means. [1]
  17. Summer 2023, AS Unit 1, Q1(b)(i) (3 marks): Describe and explain the effect of pH on the activity of lysozyme. [3]
  18. Summer 2023, AS Unit 1, Q1(b)(ii) (2 marks): Lysozyme has a wider range of pH activity than many other enzymes. I. Use Graph 1.3 to find the range of pH over which the activity of lysozyme is more than 50%
  19. Summer 2022, AS Unit 1, Q5(c)(i) (5 marks): Using Graph 5.3 and your own knowledge, compare the relative lactase activity of the free and immobilised lactase at the following temperatures. Expl
  20. Summer 2022, AS Unit 1, Q6(c) (2 marks): Thrombin catalyses the hydrolysis of an arginine-glycine bond in fibrinogen as shown in Image 6.3. Image 6.3 Image 6.4 ARG GLY GLY ARG H2O X ARG GLY Name the ty
  21. Summer 2022, AS Unit 1, Q6(d)(i) (4 marks): Using your knowledge of enzymes, identify and explain the type of inhibition shown by hirudin and suggest how hirudin enables the leech to feed effectively. [4]
  22. Summer 2022, AS Unit 1, Q6(d)(ii) (1 mark): Leeches for medical use are farmed in South Wales as a source of hirudin. Suggest a use for hirudin in medicine. [1]
  23. Summer 2019, AS Unit 1, Q3(a)(i) (4 marks): Using your knowledge of enzymes, explain why: I. it was necessary for a buffer to be added to the solutions; [2] II. all test tubes were placed in a thermostati
  24. Summer 2019, AS Unit 1, Q3(a)(ii) (1 mark): Calculate the mean time taken for the 4% milk powder suspension to become transparent. Write your answer in the table. [1]
  25. Summer 2019, AS Unit 1, Q3(a)(iii) (4 marks): Plot the mean data on the graph paper provided. Range bars should also be added to the graph. [4] 120 110 100 90 80 70 60 50 40 0 1 2 3 4 5 Concentration of mil
  26. Summer 2019, AS Unit 1, Q3(b)(i) (1 mark): Estimate the percentage concentration of casein in these two suspensions. [1] X: Y:
  27. Summer 2019, AS Unit 1, Q3(b)(ii) (2 marks): The student had more confidence in the estimate for suspension X than the estimate for suspension Y. Use the graph to explain the reason for this statement. [2]
  28. Summer 2019, AS Unit 1, Q3(b)(iii) (2 marks): Suggest two sources of inaccuracy in this experiment. [2]
  29. Summer 2019, AS Unit 1, Q5(b)(i) (3 marks): Using your knowledge of enzymes explain why this biosensor will only detect the presence of glucose. [3]
  30. Summer 2019, AS Unit 1, Q5(b)(ii) (2 marks): With reference to the information given, explain how the biosensor could be used to give a measurement of the glucose concentration. [2]
  31. Summer 2019, AS Unit 1, Q5(c) (4 marks): Arabinose is a monosaccharide that can also be used as a sweetener. The diagram below shows the structural formula of arabinose. H O OH OH H OH H H H H OH Arabi
  32. Summer 2018, Unit 3, Q6(b)(i) (2 marks): Suggest why the shaded regions are similar in all organisms. [2]
  33. Summer 2018, Unit 3, Q6(b)(ii) (2 marks): Suggest why cytochrome c detaches from the cytochrome oxidase molecule when the electrons it carries are removed. [2]
  34. Summer 2018, AS Unit 1, Q6(a)(i) (1 mark): State what is represented by the region labelled T. [1]
  35. Summer 2018, AS Unit 1, Q6(a)(ii) (1 mark): Draw a curve on the diagram to show the change in energy level when alcohol dehydrogenase is present. [1]
  36. Summer 2018, AS Unit 1, Q6(b) (3 marks): Describe how alcohol dehydrogenase can catalyse the conversion of ethanol into ethanal. [3]
  37. Summer 2018, AS Unit 1, Q6(c)(i) (2 marks): Calculate the rate of reaction at Q. [2] rate = mg s–1
  38. Summer 2018, AS Unit 1, Q6(c)(ii) (4 marks): What conclusions can be drawn that would account for the difference in rate at P and at Q? [4]
  39. Summer 2018, AS Unit 1, Q6(d) (5 marks): Ethylene glycol is a colourless, odourless, sweet liquid, commonly found in antifreeze. It is highly toxic if ingested because once inside the body ethylene gly
  40. Summer 2017, AS Unit 1, Q4(a) (1 mark): State the term given to enzymes which work within specific compartments inside cells. [1] Triacetin is a colourless triglyceride and can be hydrolysed by bacter
  41. Summer 2017, AS Unit 1, Q4(b)(i) (2 marks): Identify the independent and dependent variables in this investigation. [2] independent dependent
  42. Summer 2017, AS Unit 1, Q4(b)(ii) (1 mark): Explain why the solutions were left in the water bath for 5 minutes before combining and mixing. [1]
  43. Summer 2017, AS Unit 1, Q4(b)(iii) (3 marks): Explain why it would be inappropriate to use a buffer solution in this experiment. [3] The results of the investigation are shown below. 90 80 70 60 50 40 30 20
  44. Summer 2017, AS Unit 1, Q4(c)(i) (3 marks): digestion per second at 40°C. Give your answer in standard form. [3] Rate = g s–1
  45. Summer 2017, AS Unit 1, Q4(c)(ii) (1 mark): Suggest one source of inaccuracy in this experimental method. [1]
  46. Summer 2017, AS Unit 1, Q4(c)(iii) (4 marks): It was not possible to determine the optimum temperature for this enzyme in this experiment. Explain why and suggest how the design might be improved. [4]
  47. Summer 2016, AS Unit 1, Q4(a)(iv) (2 marks): A student was provided with two beakers, one containing sucrose and the other containing sucrase. Describe one biochemical test that the student could have carr
  48. Summer 2016, AS Unit 1, Q4(b)(i) (2 marks): State two additional variables that the student should control to ensure that the results recorded would be repeatable. [2]
  49. Summer 2016, AS Unit 1, Q4(b)(ii) (4 marks): The results are shown in the table below. Absorbance of light (au) pH of sucrose and sucrase solution trial 1 trial 2 trial 3 mean 3 0.84 0.63 0.76 0.74 4 0.89
  50. Summer 2016, AS Unit 1, Q4(b)(iii) (3 marks): What conclusions can be drawn from the data regarding the hypothesis being tested? [3]
  51. Summer 2016, AS Unit 1, Q4(b)(iv) (2 marks): The student was also provided with the calibration curve below in order to calculate the concentration of glucose produced during the investigation. The colour
  52. Summer 2016, AS Unit 1, Q4(c) (2 marks): With reference to the data explain how, and why, you would modify the method to determine the optimum pH more accurately. [2]
  53. Summer 2016, AS Unit 1, Q6 (9 marks): Pyrophosphatase is an enzyme found inside the nucleus of cells and is involved in DNA replication. The enzyme catalyses the conversion of a molecule of pyrophos

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