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Detecting stimuli and plant responses: Edexcel A‑Level Biology A questions

Every Edexcel A-Level Biology A exam question on Detecting stimuli and plant responses (specification points 8.5–8.6), 2016–2025, with its mark scheme and examiner’s report.

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1,749 questions

  1. Q4(a)

    June 2025 · Paper 2

    3 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2025 Paper 2, question 4(a): Describe the pathway taken by nerve impulses from sensory cells in the eye to the part of the brain that forms the images. (3)

  2. Q4(b)

    June 2025 · Paper 2

    3 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2025 Paper 2, question 4(b): The fovea is part of the retina. In one study, the mean density of photosensitive cells in the fovea was found to be 164 000 ± 24 000 per mm2. The mean radius o

  3. Q8(a)(i)

    June 2025 · Paper 2

    2 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2025 Paper 2, question 8(a)(i): State two ways that the active form of phytochrome (PFR) can be converted to the inactive form (PR). (2) 1 2

  4. Q8(a)(ii)

    June 2025 · Paper 2

    3 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2025 Paper 2, question 8(a)(ii): Arabidopsis is known as a long-day plant. Explain why Arabidopsis will flower when each day has 16 hours of light. (3)

  5. Q8(b)(ii)

    June 2025 · Paper 2

    6 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2025 Paper 2, question 8(b)(ii): Phytochromes and auxin are involved in the response of Arabidopsis plants to the presence of other plants growing nearby. Arabidopsis plants grow taller if ther

  6. Q7(b)(i)

    June 2024 · Paper 2

    2 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2024 Paper 2, question 7(b)(i): Describe the process of rhodopsin formation in rod cells after exposure to bright light. (2)

  7. Q8(b)(i)

    June 2024 · Paper 2

    1 markDetecting stimuli and plant responses
    The whole paper ↗
    June 2024 Paper 2, question 8(b)(i): What happens to phytochrome in the dark? (1) Converted To phytochrome A Rapidly far red B Rapidly red C Slowly far red D Slowly red

  8. Q8(b)(ii)

    June 2024 · Paper 2

    3 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2024 Paper 2, question 8(b)(ii): Explain how the response of phytochrome to a light stimulus can cause an increase in plant growth. (3)

  9. Q1(b)

    June 2024 · Paper 3

    3 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2024 Paper 3, question 1(b): One role of IAA is to stimulate the phototropic response of shoots. Describe how IAA causes a phototropic response in the shoots of a plant. (3)

  10. Q1(c)(i)

    June 2024 · Paper 3

    2 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2024 Paper 3, question 1(c)(i): Explain why the scientists used plants homozygous for the normal and the mutant tir1 gene in this investigation. (2)

  11. Q1(c)(ii)

    June 2024 · Paper 3

    1 markDetecting stimuli and plant responses
    The whole paper ↗
    June 2024 Paper 3, question 1(c)(ii): Calculate the percentage decrease in mean number of lateral roots for thale cress with the mutant tir1 gene compared to thale cress with the normal tir1 gene at

  12. Q1(c)(iii)

    June 2024 · Paper 3

    2 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2024 Paper 3, question 1(c)(iii): Deduce the effect of the mutation in the tir1 gene on the response of thale cress to IAA. (2)

  13. Q9(b)

    June 2023 · Paper 2

    4 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2023 Paper 2, question 9(b): Rod cells form synapses with bipolar neurones. Describe how movement of sodium ions in a rod cell affects depolarisation in a bipolar neurone. (4)

  14. Q9(c)(i)

    June 2023 · Paper 2

    2 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2023 Paper 2, question 9(c)(i): Describe the role of the photosensitive pigment phytochrome in the flowering of long‑day plants. (2)

  15. Q9(c)(ii)

    June 2023 · Paper 2

    3 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2023 Paper 2, question 9(c)(ii): Devise an investigation to find out if a species of plant is a long-day plant or a short‑day plant. (3)

  16. Q1(a)(i)

    June 2022 · Paper 3

    2 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2022 Paper 3, question 1(a)(i): Describe two conclusions that can be drawn from the results of this investigation. (2)

  17. Q1(a)(ii)

    June 2022 · Paper 3

    2 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2022 Paper 3, question 1(a)(ii): The results of this investigation were analysed using the Student’s t-test. A p value of 0.05 was used to interpret the results of the t-test. Explain what a p

  18. Q1(b)(i)

    June 2022 · Paper 3

    1 markDetecting stimuli and plant responses
    The whole paper ↗
    June 2022 Paper 3, question 1(b)(i): Give one abiotic factor, other than pH, that would need to be controlled in this investigation. (1)

  19. Q1(b)(ii)

    June 2022 · Paper 3

    2 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2022 Paper 3, question 1(b)(ii): Calculate the difference in the rates of change in cell length from 30 to 60 minutes, in the presence of IAA and in the absence of IAA. (2) Answer

  20. Q1(c)

    June 2022 · Paper 3

    3 marksDetecting stimuli and plant responses
    The whole paper ↗
    June 2022 Paper 3, question 1(c): Explain how the evidence from these investigations indicates that plant hormones are involved in the phototropic response of oat coleoptiles. (3)
All 32 questions on Detecting stimuli and plant responses, as a list
  1. June 2025, Paper 2, Q4(a) (3 marks): Describe the pathway taken by nerve impulses from sensory cells in the eye to the part of the brain that forms the images. (3)
  2. June 2025, Paper 2, Q4(b) (3 marks): The fovea is part of the retina. In one study, the mean density of photosensitive cells in the fovea was found to be 164 000 ± 24 000 per mm2. The mean radius o
  3. June 2025, Paper 2, Q8(a)(i) (2 marks): State two ways that the active form of phytochrome (PFR) can be converted to the inactive form (PR). (2) 1 2
  4. June 2025, Paper 2, Q8(a)(ii) (3 marks): Arabidopsis is known as a long-day plant. Explain why Arabidopsis will flower when each day has 16 hours of light. (3)
  5. June 2025, Paper 2, Q8(b)(ii) (6 marks): Phytochromes and auxin are involved in the response of Arabidopsis plants to the presence of other plants growing nearby. Arabidopsis plants grow taller if ther
  6. June 2024, Paper 2, Q7(b)(i) (2 marks): Describe the process of rhodopsin formation in rod cells after exposure to bright light. (2)
  7. June 2024, Paper 2, Q8(b)(i) (1 mark): What happens to phytochrome in the dark? (1) Converted To phytochrome A Rapidly far red B Rapidly red C Slowly far red D Slowly red
  8. June 2024, Paper 2, Q8(b)(ii) (3 marks): Explain how the response of phytochrome to a light stimulus can cause an increase in plant growth. (3)
  9. June 2024, Paper 3, Q1(b) (3 marks): One role of IAA is to stimulate the phototropic response of shoots. Describe how IAA causes a phototropic response in the shoots of a plant. (3)
  10. June 2024, Paper 3, Q1(c)(i) (2 marks): Explain why the scientists used plants homozygous for the normal and the mutant tir1 gene in this investigation. (2)
  11. June 2024, Paper 3, Q1(c)(ii) (1 mark): Calculate the percentage decrease in mean number of lateral roots for thale cress with the mutant tir1 gene compared to thale cress with the normal tir1 gene at
  12. June 2024, Paper 3, Q1(c)(iii) (2 marks): Deduce the effect of the mutation in the tir1 gene on the response of thale cress to IAA. (2)
  13. June 2023, Paper 2, Q9(b) (4 marks): Rod cells form synapses with bipolar neurones. Describe how movement of sodium ions in a rod cell affects depolarisation in a bipolar neurone. (4)
  14. June 2023, Paper 2, Q9(c)(i) (2 marks): Describe the role of the photosensitive pigment phytochrome in the flowering of long‑day plants. (2)
  15. June 2023, Paper 2, Q9(c)(ii) (3 marks): Devise an investigation to find out if a species of plant is a long-day plant or a short‑day plant. (3)
  16. June 2022, Paper 3, Q1(a)(i) (2 marks): Describe two conclusions that can be drawn from the results of this investigation. (2)
  17. June 2022, Paper 3, Q1(a)(ii) (2 marks): The results of this investigation were analysed using the Student’s t-test. A p value of 0.05 was used to interpret the results of the t-test. Explain what a p
  18. June 2022, Paper 3, Q1(b)(i) (1 mark): Give one abiotic factor, other than pH, that would need to be controlled in this investigation. (1)
  19. June 2022, Paper 3, Q1(b)(ii) (2 marks): Calculate the difference in the rates of change in cell length from 30 to 60 minutes, in the presence of IAA and in the absence of IAA. (2) Answer
  20. June 2022, Paper 3, Q1(c) (3 marks): Explain how the evidence from these investigations indicates that plant hormones are involved in the phototropic response of oat coleoptiles. (3)
  21. November 2021, Paper 2, Q6(a)(iv) (2 marks): Give reasons why the infected alfalfa plant cells are grown on agar containing IAA in stage 5. (2)
  22. November 2021, Paper 2, Q10(a) (5 marks): A current is produced by a rod cell when ions move through the cell surface membrane of a rod cell. The graph shows the effect of increasing light intensity on
  23. November 2021, Paper 3, Q1(b) (4 marks): Describe the role of IAA (auxin) in the phototropic response of plants. (4)
  24. October 2020, Paper 2, Q3(a) (4 marks): The diagram shows an oat seedling in part of a field. coleoptile of oat seedling surface of soil in the field oat seed Cells in the tip of the oat coleoptile re
  25. October 2020, Paper 2, Q3(b)(i) (1 mark): Which row correctly describes the effects of sunlight on phytochrome? (1) Change in form of Speed of change phytochrome A PFR to PR slow B PFR to PR rapid C PR
  26. October 2020, Paper 2, Q3(b)(ii) (1 mark): Phytochrome can be described as (1) A a form of opsin B a photosensitive pigment C an isomer of retinal D a type of cytochrome
  27. October 2020, Paper 2, Q3(b)(iii) (1 mark): Give one example of a growth response of a plant that is affected by phytochrome. (1)
  28. October 2020, Paper 3, Q7(a) (5 marks): Describe how ‘eyes relay visual information’ to the brain (paragraph 2). (5)
  29. June 2019, Paper 2, Q9(c) (3 marks): When the child was shown the cheeseburger, information would have been sent from the eye to the brain. Describe the role of sodium ions in the functioning of a
  30. June 2019, Paper 3, Q5(b)(i) (3 marks): Explain why the plants were placed in a box in complete darkness. (3)
  31. June 2019, Paper 3, Q5(b)(ii) (2 marks): The mean curvatures of the stems and the roots are shown in the graphs. Mean curvature of the stem in degrees 70 60 50 40 30 20 Key 10 *x.. . →* upright lettuce
  32. June 2018, Paper 2, Q4(a)(i) (1 mark): The non-protein part of the light-absorbing pigment in the rod cells of the retina is called (1) A IAA B opsin C retinal D rhodopsin

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