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Population size and ecosystems: WJEC A‑Level Biology questions

Every WJEC A-Level Biology exam question on 3.5 Population size and ecosystems, 2016–2025, with its mark scheme and examiner’s report.

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1,223 questions

  1. Q4(a)

    Summer 2025 · Unit 3

    2 marks3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2025 Unit 3, question 4(a): State what is meant by the term transect. Explain why a transect is preferred over random distribution of quadrats in this situation. [2] Image 4.1 shows the sh

  2. Q4(b)

    Summer 2025 · Unit 3

    1 mark3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2025 Unit 3, question 4(b): Use Image 4.1 to describe the distribution of the three species of seaweed that belong to the same genus across the upper, mid and lower shore. [1]

  3. Q4(c)(i)

    Summer 2025 · Unit 3

    2 marks3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2025 Unit 3, question 4(c)(i): The students decided to start their survey at 05:30 on September 17th. I. Use Image 4.2 to suggest why they selected that day to carry out their survey. [1] II.

  4. Q4(c)(ii)

    Summer 2025 · Unit 3

    2 marks3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2025 Unit 3, question 4(c)(ii): Use information from Images 4.1 and 4.2 to calculate how many hours the organisms living in quadrat 7 would be exposed to air on September 17th. Draw lines on I

  5. Q4(d)

    Summer 2025 · Unit 3

    2 marks3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2025 Unit 3, question 4(d): Image 4.3 shows photographs of two of the species of seaweed included in the study. Unlike higher plants, seaweeds do not have roots, stems and leaves. Instead,

  6. Q4(e)(ii)

    Summer 2025 · Unit 3

    2 marks3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2025 Unit 3, question 4(e)(ii): Use the actual thicknesses of x–x and y–y shown in the box on Image 4.4 to calculate the percentage of the thallus that is made up of core. [2] Percentage of th

  7. Q4(f)(i)

    Summer 2025 · Unit 3

    1 mark3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2025 Unit 3, question 4(f)(i): State an appropriate statistical test that could be used to determine whether the difference between two means is significant. [1]

  8. Q4(f)(ii)

    Summer 2025 · Unit 3

    1 mark3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2025 Unit 3, question 4(f)(ii): Use the information given above to state the Null Hypothesis for their test. [1]

  9. Q4(f)(iii)

    Summer 2025 · Unit 3

    2 marks3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2025 Unit 3, question 4(f)(iii): Suggest two ways that the student’s plan could be improved to increase confidence in their results. [2]

  10. Q3(c)

    Summer 2024 · Unit 3

    3 marks3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2024 Unit 3, question 3(c): Name the soil bacteria that act on nitrite ions and explain how the soil bacteria change the nitrite ions so they are able to continue to circulate in the nitro

  11. Q6(a)(i)

    Summer 2024 · Unit 3

    1 mark3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2024 Unit 3, question 6(a)(i): State the name given to the type of sampling technique used in this survey. [1]

  12. Q6(a)(ii)

    Summer 2024 · Unit 3

    2 marks3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2024 Unit 3, question 6(a)(ii): The swamp in this survey could be correctly termed as both a habitat and an ecosystem. Distinguish between the terms, habitat and ecosystem. [2]

  13. Q6(a)(iii)

    Summer 2024 · Unit 3

    2 marks3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2024 Unit 3, question 6(a)(iii): Using the information provided in Image 6.1, state the ranges of water depth over which duckweed and pondweed were found. [2] Duckweed Pondweed Image 6.2 shows

  14. Q6(b)(i)

    Summer 2024 · Unit 3

    1 mark3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2024 Unit 3, question 6(b)(i): With reference to Image 6.2 suggest why duckweed outcompetes pondweed in the shallower part of the range. [1]

  15. Q6(b)(ii)

    Summer 2024 · Unit 3

    3 marks3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2024 Unit 3, question 6(b)(ii): Name two nutrients for which the plants will compete and explain what each nutrient is used for in the plants. [3]

  16. Q6(b)(iii)

    Summer 2024 · Unit 3

    3 marks3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2024 Unit 3, question 6(b)(iii): Explain why the concentration of nutrients is likely to be greater at the bottom of the pools and suggest a hypothesis to explain why pondweed outcompetes duckw

  17. Q2(d)(i)

    Summer 2024 · Unit 4

    2 marks3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2024 Unit 4, question 2(d)(i): One simple conclusion from this data is that higher soil temperatures reduce the number of mature wheat plants per square metre. State four other factors that c

  18. Q2(e)(i)

    Summer 2023 · Unit 3

    1 mark3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2023 Unit 3, question 2(e)(i): Calculate the rate at which krill use diatom biomass for respiration (R). [1] Rate = . ..... . g m –3 day –1

  19. Q2(e)(ii)

    Summer 2023 · Unit 3

    3 marks3.5 Population size and ecosystems
    The whole paper ↗
    Summer 2023 Unit 3, question 2(e)(ii): It is estimated that a single blue whale needs to consume 8 000 kg of biomass per day. The biomass of krill was estimated as 25 g m –3. Calculate the volume of

  20. Q4(a)

    Summer 2023 · Unit 3

    1 mark3.5 Population size and ecosystems
    Mark scheme (PDF)
    The whole paper ↗
    Summer 2023 Unit 3, question 4(a): Using the terms in brackets from the above equation, write another equation which shows the relationship between the terms when the population size remains cons
All 59 questions on Population size and ecosystems, as a list
  1. Summer 2025, Unit 3, Q4(a) (2 marks): State what is meant by the term transect. Explain why a transect is preferred over random distribution of quadrats in this situation. [2] Image 4.1 shows the sh
  2. Summer 2025, Unit 3, Q4(b) (1 mark): Use Image 4.1 to describe the distribution of the three species of seaweed that belong to the same genus across the upper, mid and lower shore. [1]
  3. Summer 2025, Unit 3, Q4(c)(i) (2 marks): The students decided to start their survey at 05:30 on September 17th. I. Use Image 4.2 to suggest why they selected that day to carry out their survey. [1] II.
  4. Summer 2025, Unit 3, Q4(c)(ii) (2 marks): Use information from Images 4.1 and 4.2 to calculate how many hours the organisms living in quadrat 7 would be exposed to air on September 17th. Draw lines on I
  5. Summer 2025, Unit 3, Q4(d) (2 marks): Image 4.3 shows photographs of two of the species of seaweed included in the study. Unlike higher plants, seaweeds do not have roots, stems and leaves. Instead,
  6. Summer 2025, Unit 3, Q4(e)(ii) (2 marks): Use the actual thicknesses of x–x and y–y shown in the box on Image 4.4 to calculate the percentage of the thallus that is made up of core. [2] Percentage of th
  7. Summer 2025, Unit 3, Q4(f)(i) (1 mark): State an appropriate statistical test that could be used to determine whether the difference between two means is significant. [1]
  8. Summer 2025, Unit 3, Q4(f)(ii) (1 mark): Use the information given above to state the Null Hypothesis for their test. [1]
  9. Summer 2025, Unit 3, Q4(f)(iii) (2 marks): Suggest two ways that the student’s plan could be improved to increase confidence in their results. [2]
  10. Summer 2024, Unit 3, Q3(c) (3 marks): Name the soil bacteria that act on nitrite ions and explain how the soil bacteria change the nitrite ions so they are able to continue to circulate in the nitro
  11. Summer 2024, Unit 3, Q6(a)(i) (1 mark): State the name given to the type of sampling technique used in this survey. [1]
  12. Summer 2024, Unit 3, Q6(a)(ii) (2 marks): The swamp in this survey could be correctly termed as both a habitat and an ecosystem. Distinguish between the terms, habitat and ecosystem. [2]
  13. Summer 2024, Unit 3, Q6(a)(iii) (2 marks): Using the information provided in Image 6.1, state the ranges of water depth over which duckweed and pondweed were found. [2] Duckweed Pondweed Image 6.2 shows
  14. Summer 2024, Unit 3, Q6(b)(i) (1 mark): With reference to Image 6.2 suggest why duckweed outcompetes pondweed in the shallower part of the range. [1]
  15. Summer 2024, Unit 3, Q6(b)(ii) (3 marks): Name two nutrients for which the plants will compete and explain what each nutrient is used for in the plants. [3]
  16. Summer 2024, Unit 3, Q6(b)(iii) (3 marks): Explain why the concentration of nutrients is likely to be greater at the bottom of the pools and suggest a hypothesis to explain why pondweed outcompetes duckw
  17. Summer 2024, Unit 4, Q2(d)(i) (2 marks): One simple conclusion from this data is that higher soil temperatures reduce the number of mature wheat plants per square metre. State four other factors that c
  18. Summer 2023, Unit 3, Q2(e)(i) (1 mark): Calculate the rate at which krill use diatom biomass for respiration (R). [1] Rate = . ..... . g m –3 day –1
  19. Summer 2023, Unit 3, Q2(e)(ii) (3 marks): It is estimated that a single blue whale needs to consume 8 000 kg of biomass per day. The biomass of krill was estimated as 25 g m –3. Calculate the volume of
  20. Summer 2023, Unit 3, Q4(a) (1 mark): Using the terms in brackets from the above equation, write another equation which shows the relationship between the terms when the population size remains cons
  21. Summer 2023, Unit 3, Q4(b)(i) (2 marks): From the figures given in the method and Table 4.1 estimate the total number of frogs in the woodland, using the following formula: [2] N = Mn m Where, • N = nu
  22. Summer 2023, Unit 3, Q4(b)(ii) (1 mark): Explain why the chosen method of marking the frogs might have affected the estimate of the frog population. [1]
  23. Summer 2023, Unit 3, Q4(d)(i) (3 marks): Calculate the rate of decline in number of tadpoles for pond 1 at day 10 Give your answer to two significant figures. [3] Rate of decline .. .. .. tadpoles m–3
  24. Summer 2023, Unit 3, Q4(d)(ii) (3 marks): Using the information from Graph 4.2 it was concluded that a density-dependent factor was causing the change in the tadpole populations. State the evidence for
  25. Summer 2023, Unit 3, Q4(e)(i) (2 marks): With reference to Graph 4.3, state two conclusions that can be drawn about the effect of density and selection on the rate of development of tadpoles in the thr
  26. Summer 2023, Unit 3, Q4(e)(ii) (2 marks): Another group of scientists said that it was not valid to use the results from tank 2 and tank 3 to make a conclusion about the effect of selection. Suggest why
  27. Summer 2023, Unit 3, Q6(a)(ii) (2 marks): I. On Image 6.1, label one of the arrows with an X to show a process which involves micro-organisms. II. Explain the role of micro-organisms in this process. [2
  28. Summer 2023, Unit 4, Q4(a)(i) (2 marks): State two conclusions that you could draw from the data in Graph 4.2A and Graph 4.2B. [2]
  29. Summer 2023, Unit 4, Q4(a)(ii) (1 mark): State the modes for the two sets of data. [1] Sheltered rocky shore mode = Exposed rocky shore mode = Two groups of A level students carried out the same type o
  30. Summer 2023, Unit 4, Q4(b)(i) (1 mark): State the null hypothesis for this experiment. [1]
  31. Summer 2023, Unit 4, Q4(b)(ii) (1 mark): State the degrees of freedom which should be used. [1] Table 4.4 shows the critical values for a two-tailed test. Table 4.4 Probability Degrees of 0.1 0.05 0.01
  32. Summer 2023, Unit 4, Q4(b)(iii) (3 marks): Use Table 4.4 to determine whether you would accept or reject the null hypothesis. Explain how you have come to this conclusion. [3]
  33. Summer 2023, Unit 4, Q4(c) (3 marks): Suggest one density-independent and two density-dependent factors which could account for the difference in shell length. [3] Density-independent factor Density
  34. Summer 2022, Unit 3, Q2(b)(i) (1 mark): Give the full name of the biological process involved in forest regeneration. [1]
  35. Summer 2022, Unit 3, Q2(b)(ii) (3 marks): Using relevant technical terms, describe and explain the process of forest regeneration. [3]
  36. Summer 2019, Unit 3, Q2(a)(i) (1 mark): Give one reason why not all of the solar energy falling on the producers is used to form biomass. [1]
  37. Summer 2019, Unit 3, Q2(a)(ii) (2 marks): Using the information given in the diagram, calculate the percentage of energy from the Sun that is fixed by photosynthesis. [2] Percentage of energy = %
  38. Summer 2019, Unit 3, Q5(a)(i) (2 marks): State the type of competition occurring in this area and what the mature adults could be competing for. [2]
  39. Summer 2019, Unit 3, Q5(a)(ii) (1 mark): Scientists removed Chthamalus from the upper area continually for several weeks and observed that Semibalanus did not colonise this area. Suggest a possible exp
  40. Summer 2019, Unit 3, Q5(a)(iii) (2 marks): Scientists then removed Semibalanus from the lower area continually for several weeks and observed that Chthamalus were found in this cleared area. Give an expl
  41. Summer 2019, Unit 3, Q5(b)(i) (4 marks): Describe the method by which reliable data would have been collected. [4]
  42. Summer 2018, Unit 3, Q3(a)(i) (4 marks): The main source of carbon for these leaves is from the air inside the pod, not the atmosphere. Describe how carbon inside the pod is made available for use by t
  43. Summer 2018, Unit 3, Q3(a)(ii) (3 marks): Describe how nitrogen is made available for use by these leaves. [3]
  44. Summer 2018, Unit 3, Q5(a) (2 marks): Explain why the dry mass was lower in Area 2 [2]
  45. Summer 2018, Unit 3, Q5(b) (2 marks): Using the information from Areas 1 and 3, calculate the net primary productivity of the grassland. Give your answer to 2 decimal places. [2] Net primary product
  46. Summer 2018, Unit 3, Q5(c) (2 marks): Suggest why this method cannot be used to calculate the net primary productivity of tropical rainforest. [2]
  47. Summer 2018, Unit 3, Q5(d) (2 marks): To find the dry mass the ecologists dried the grass samples in an oven at 65 °C. Describe how the ecologists would be confident that all the water had been remo
  48. Summer 2018, Unit 3, Q8 (9 marks): The photograph below shows a group of young male cheetahs eating a wildebeest. A team of scientists from the Mara Cheetah Project estimated that the adult popul
  49. Summer 2018, Unit 4, Q2(d)(i) (2 marks): Another species of grass, common bent (Agrostis tenuis), is also copper tolerant and is found growing in polluted mine sites together with sweet vernal grass. T
  50. Summer 2018, Unit 4, Q2(d)(ii) (1 mark): State and explain whether high copper concentrations act in a density dependent or density independent way. [1]
  51. Summer 2018, Unit 4, Q7(b)(v) (1 mark): Explain why a standard deviation is used for the BMD scan. [1]
  52. Summer 2017, Unit 3, Q6(a)(i) (3 marks): Describe how and explain why the sites are selected at random. [3] The table below shows the mean number of each species in a 1m2 area after five years. Mean nu
  53. Summer 2017, Unit 3, Q6(a)(ii) (3 marks): In the first year the scientists only found four different species in the area. Identify the type of succession that has taken place in the five years of the st
  54. Summer 2017, Unit 3, Q6(a)(iii) (2 marks): Suggest what would happen to the number of animal species in this area. Explain your answer. [2]
  55. Summer 2017, Unit 3, Q6(b)(i) (3 marks): Explain why they are able to survive in soils with low nitrogen levels. [3]
  56. Summer 2017, Unit 3, Q6(b)(ii) (3 marks): Rhizobium contain the enzyme nitrogenase which is responsible for fixing atmospheric nitrogen. This enzyme is inhibited if oxygen levels are high. The root nodu
  57. Summer 2017, Unit 3, Q6(c)(i) (1 mark): Explain why bog is described as the climax community. [1]
  58. Summer 2017, Unit 3, Q6(c)(ii) (2 marks): Explain why trees are unable to survive in waterlogged soils. [2] The photograph shows a plant found on the bog called sundew (Drosera rotundifolia). This is an
  59. Summer 2017, Unit 3, Q6(d) (3 marks): Suggest why insectivorous plants such as sundew rely on catching prey. [3]

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