Decomposition, DNA profiling and forensics: Edexcel International A Level Biology questions

Every Edexcel International A Level Biology exam question on Decomposition, DNA profiling and forensics (specification points 6.16–6.20), 2019–2025, with its mark scheme and examiner’s report.

All 75 questions on Decomposition, DNA profiling and forensics, as a list

June 2025, Unit 4, Q3(a) (1 mark): Which of the following can also be used to determine the time of death of a mammal? (1) A dendrochronology and degree of muscle contraction B degree of muscle c
June 2025, Unit 4, Q3(b)(i) (2 marks): A mammal had been dead for 15 hours. Calculate the body temperature of this mammal in °C. Use the formula: 5 × (temperature in F 32) Temperature in °C = 9 Give
June 2025, Unit 4, Q3(b)(ii) (3 marks): Explain how this cooling curve would change if the mammal had more body fat. (3)
June 2025, Unit 4, Q3(b)(iii) (3 marks): The equation for the cooling curve shown in the graph can be used to determine the time of death. Write the equation for this cooling curve, using the format: y
June 2025, Unit 6, Q3(d) (6 marks): Bacteria in the desert soil can break down crude oil. A scientist predicted that the number of bacteria in the desert soil would increase as the crude oil was b
January 2025, Unit 4, Q2(a) (1 mark): The identification of insects present on the body can be used to estimate how long a mammal has been dead. Which method uses the numbers and species of insects
January 2025, Unit 4, Q2(b) (4 marks): Explain why body temperature and the degree of muscle contraction can be used to determine the time of death of a mammal. (4)
January 2025, Unit 4, Q5(b)(ii) (5 marks): Explain how the conditions in the peat bog preserved the body of this man. Use the information in the question and your own knowledge to support your answer. (5
January 2025, Unit 6, Q4(a) (2 marks): Describe preliminary practical work that you might undertake to ensure your proposed method would provide quantitative results. (2)
January 2025, Unit 6, Q4(b) (9 marks): Devise a detailed method, including how you would control and monitor important variables. (9)
January 2025, Unit 6, Q4(d) (2 marks): Suggest two limitations of your proposed method. (2)
October 2024, Unit 4, Q2(a)(i) (2 marks): Explain why PCR was used on the DNA samples. (2)
October 2024, Unit 4, Q2(a)(ii) (2 marks): Taq (DNA) polymerase is used in PCR. Describe the role of Taq (DNA) polymerase. (2)
October 2024, Unit 4, Q2(b)(ii) (3 marks): The results of the gel electrophoresis were used to identify the plants that contained the resistance genes. Deduce the types of plants that would have supplied
October 2024, Unit 4, Q4(a)(i) (1 mark): Which is the term used to describe the use of insects in determining the time and place of death of a mammal? (1) A chromatography B dendrochronology C forensic
October 2024, Unit 4, Q4(a)(ii) (1 mark): Which of the following factors provides information about the time of death of a mammal? 1. species of insect 2. size of larvae, e.g. maggots 3. stages in devel
October 2024, Unit 4, Q4(b)(i) (1 mark): Which is the most accurate method of measuring the body temperature of a human corpse to determine time of death? (1) A placing a temperature‑sensitive strip on
October 2024, Unit 4, Q4(b)(ii) (1 mark): Time of death can be estimated by determining the fall in body temperature. Which row of the table shows how more clothing and higher ambient temperature would
October 2024, Unit 4, Q4(c)(i) (3 marks): The graph shows the changes in three characteristics of muscle with time after the death of a mammal: • ATP • lactic acid • pH lactic acid Changes in the charac
October 2024, Unit 4, Q4(c)(ii) (3 marks): The graph shows the changes in the extent of muscle contraction with time after death. Extent of muscle contraction 0 6 12 18 24 30 36 42 Time after death / hou
June 2024, Unit 4, Q4(b)(i) (1 mark): Decomposition was measured as a decrease in dry mass of the leaves. Suggest why dry mass was measured and not wet mass. (1)
June 2024, Unit 4, Q4(b)(ii) (2 marks): Calculate the rate of decrease in percentage dry mass between 30 days and 120 days for the sugar maple leaves. Give your answer to two significant figures. (2)
June 2024, Unit 4, Q4(b)(iii) (2 marks): Describe two conclusions that can be made about the decomposition of sugar maple leaves compared with the white oak leaves. (2)
June 2024, Unit 4, Q4(c)(i) (1 mark): Calculate how many times greater the biomass of bacteria on the sugar maple leaves is after 30 days compared with the biomass of bacteria at 0 days. (1) Answer
June 2024, Unit 4, Q4(c)(ii) (2 marks): Suggest why the increase in biomass of bacteria after 30 days is greater on the sugar maple leaves than it is on the white oak leaves. Give a reason for your an
June 2024, Unit 4, Q4(c)(iii) (2 marks): Suggest why the biomass of bacteria on the white oak leaves decreased after 90 days. Give a reason for your answer. (2)
October 2023, Unit 4, Q8(a)(iii) (3 marks): Explain the importance of enzymes produced by microorganisms in decomposition. (3)
June 2023, Unit 4, Q2(b)(i) (1 mark): Which two procedures could have been used to analyse the DNA? (1) A electron microscopy followed by PCR B entomology followed by electron microscopy C gel elect
June 2023, Unit 4, Q2(b)(ii) (3 marks): Describe how analysis of the DNA would show that these two other bears were female, and not related to each other or to Hank. (3)
June 2023, Unit 4, Q9(a)(i) (3 marks): Describe how the time of death of a person can be estimated using this method. (3)
June 2023, Unit 4, Q9(a)(ii) (2 marks): Explain the limitations of this method. (2)
June 2023, Unit 4, Q9(b)(i) (1 mark): Suggest why this study used rat and pig corpses instead of human corpses. (1)
June 2023, Unit 4, Q9(b)(ii) (6 marks): The graphs show some of the results of this study. Key Rat Pig 8.0 7.5 7.0 pH of 6.5 blood 6.0 5.5 5.0 0 1 3 6 9 24 32 48 72 96 Time after death / hours 14 12 1
June 2023, Unit 4, Q9(b)(iii) (3 marks): Discuss whether these chemical tests are likely to be useful in determining the time of death of a human. (3)
June 2023, Unit 5, Q8(a) (3 marks): “Gut microorganisms play an important role… affecting human metabolic functions by decomposing the complex polysaccharides in food”. Explain the role of gut mic
January 2023, Unit 4, Q3(b)(i) (2 marks): In 2018, 8.3 × 1012 kg of plastic was produced. Only 8.7 % of this plastic was recycled. Calculate the mass of plastic that was not recycled. Express your answe
January 2023, Unit 4, Q3(b)(ii) (2 marks): Scientists are developing methods that use microorganisms to break down plastics. Some of the products produced are being used for other purposes, such as vanil
January 2023, Unit 4, Q3(b)(iii) (3 marks): One type of bacteria, Pseudomonas, uses half of the plastic it breaks down to produce its own biomass, with the rest released as carbon dioxide. Explain how the
January 2023, Unit 4, Q7(b)(iv) (2 marks): In a genetic study of these birds, DNA from the developing chick was isolated from the remains of the eggshell and amplified using PCR. To amplify a DNA molecul
January 2023, Unit 4, Q7(b)(v) (3 marks): These birds are thought to be monogamous, which means that they only mate with one bird of the opposite sex. Birds are only monogamous if the ratio of male to f
June 2022, Unit 4, Q5(a)(v) (3 marks): Describe the role of microorganisms in recycling carbon present in this food chain. (3)
January 2022, Unit 4, Q5(b)(i) (2 marks): Name three molecules, other than the mtDNA and water, that would be needed in this process. (2)
January 2022, Unit 4, Q5(b)(ii) (2 marks): Calculate the total length of time, in hours, that this process would take. Give your answer to two decimal places. . (2) Answer hours
January 2022, Unit 4, Q5(b)(iii) (3 marks): Explain how this process amplifies the DNA. Use information in the diagram to support your answer. (3)
January 2022, Unit 4, Q5(c) (3 marks): Explain how the amplified mtDNA could be used to determine the genetic relationships between these two species of crow. (3)
January 2022, Unit 4, Q8(a)(i) (2 marks): Explain why forensic entomology is the most accurate method for estimating the time of death, if this is greater than 72 hours. (2)
January 2022, Unit 4, Q8(a)(ii) (2 marks): Explain how forensic entomology can indicate if a body has been moved from the place of death. (2)
January 2022, Unit 4, Q8(b)(i) (1 mark): Suggest why the mammal was placed inside a metal cage to decompose. (1)
January 2022, Unit 4, Q8(b)(ii) (2 marks): Calculate the rate of change in mass between day 5 and day 15 of decomposition. Express your answer in kg hr–1. Give your answer to two decimal places. (2). (2)
January 2022, Unit 4, Q8(b)(iii) (4 marks): Explain the changes in mass of this mammal during decomposition. (4)
January 2022, Unit 4, Q8(b)(iv) (1 mark): Suggest why some of the insect eggs, collected from the decomposing mammal, were taken back to the laboratory and kept for a few days. (1)
January 2022, Unit 4, Q8(b)(v) (3 marks): The table shows data on some of the insects collected from this decomposing mammal. Percentage of some of the insect found at each stage of decomposition (%) Ty
October 2021, Unit 4, Q7(a)(i) (1 mark): The teabags had to be dried before weighing to remove water. One teabag contained 28 g of tea when it was buried. When it was dug up it had a wet mass of 42 g.
October 2021, Unit 4, Q7(a)(ii) (2 marks): Calculate the rate at which the relative mass of the green tea decreases in the teabags buried at 15 °C at day 30. (2) Answer
October 2021, Unit 4, Q7(a)(iii) (4 marks): Explain the difference in the decrease in relative mass of green tea in teabags buried at 15 °C and 25 °C. Use the information in the graph to support your answ
October 2021, Unit 4, Q7(a)(iv) (2 marks): Suggest why the rate of decomposition of green tea was different from that of rooibos tea. (2)
June 2021, Unit 4, Q4(b)(i) (2 marks): Explain the role of the polymerase chain reaction (PCR) in DNA profiling. (2)
June 2021, Unit 4, Q4(b)(ii) (2 marks): Explain how DNA profiling could show that these lemurs originated from the lemurs on Madagascar. (2)
June 2021, Unit 4, Q5(a) (1 mark): The time of death can be estimated using the length of insect larvae. What is the name of the method that uses insect larvae to estimate the time of death? (1)
June 2021, Unit 4, Q5(b)(i) (2 marks): Calculate the mean growth rate of these larvae from 25 to 120 hours. Include the units with your answer. (2) Answer
June 2021, Unit 4, Q5(b)(ii) (3 marks): Comment on the suitability of using this data to estimate the time of death. Use the information in the graph to support your answer. (3)
June 2021, Unit 4, Q5(b)(iii) (3 marks): Describe how the data shown in this graph could have been collected. (3)
June 2021, Unit 4, Q5(c) (4 marks): The time of death can be estimated using the body temperature of the corpse. Evaluate the use of the body temperature of a corpse to estimate the time of death.
June 2021, Unit 4, Q6(b)(iii) (3 marks): Describe how the carbon present in sugars in the plants is returned to the atmosphere in the carbon cycle. (3)
January 2021, Unit 4, Q7(a)(ii) (3 marks): Explain why the use of an enzyme to cut the DNA results in fragments, of different lengths, that can be separated by gel electrophoresis. (3)
January 2021, Unit 4, Q7(b)(i) (2 marks): Complete the table using the equation: 1 Mr = log10 MW (2) Molecular weight of DNA Relative rate of movement fragment (MW) (Mr) 100 000 10 000 0.25 0.34
January 2021, Unit 4, Q7(b)(ii) (1 mark): The diagram shows the position of a DNA fragment with a MW of 10000, after gel electrophoresis. Complete the diagram to show the position of a DNA fragment with
January 2021, Unit 4, Q7(c) (1 mark): The fragments move more slowly through a higher concentration of gel. Suggest why the fragments move more slowly through a higher concentration of gel. (1)
January 2021, Unit 4, Q8(b)(iii) (6 marks): Explain the role of decomposition in returning the carbon present in the carbohydrates in the quince fruit back into the atmosphere. Use the information given i
October 2020, Unit 4, Q2(a) (1 mark): State how the temperature of a dead body should be measured. (1)
October 2020, Unit 4, Q2(b)(i) (2 marks): Body temperature can be used to estimate the time since death using the following information: ● loss of 0.78 °C per hour for the first 12 hours after death ● a
October 2020, Unit 4, Q2(b)(ii) (2 marks): Explain why this estimate would be different if the body had been left in a colder place. (2)
October 2020, Unit 4, Q2(c) (3 marks): Explain why using body stiffness only, as shown in the table, is insufficient to estimate the time since death accurately. (3)
January 2020, Unit 4, Q2(a)(i) (2 marks): Explain why scientists think that plastics could be broken down by microorganisms. (2)
January 2020, Unit 4, Q4(b)(iii) (3 marks): This moth was seen and a specimen collected in 1887. It was not seen again in the rainforests of Malaysia until 2017. The DNA of these recently rediscovered Ori

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