Edexcel A (SNAB) A Level Biology

Topic Questions

6.1 Forensics

1a
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1 mark

Detectives investigating suspicious deaths will routinely try to establish the time of death (TOD), in order to construct a timeline of events before and after the victim's death.

Forensic scientists refer to a dead body as a cadaver. 

Which factors from the list below would forensic scientists need to take into account when assessing the victim's TOD?

  1. The cadaver's core temperature at the time of analysis
  2. The victim's gender
  3. Insect life on the cadaver
  4. Body hair coverage of the cadaver
  5. The victim's body mass
  6. The cadaver's degree of muscle contraction
  7. The position / posture of the cadaver when discovered (seated, lying down, lying on back or front etc.)
  8. The ambient temperature
  A 1, 2, 3, 6, 7 and 8
  B All except 7
  C 1, 3, 5, 6 and 8
  D 2, 4, 6 and 8

1b
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3 marks

A forensic scientist was called to the scene of a suspicious death. At 4 pm, the scientist measured the body temperature by inserting a rectal thermometer into the victim's rectum.

The cadaver's body temperature was measured to be 30.5°C.

The ambient temperature was 8°C. At this temperature, the cadaver's expected loss of heat would be 2°C in the first hour, followed by a rate of 1.5°C per hour thereafter.

Determine an estimate of the victim's likely time of death. You may assume that the deceased person's core temperature was 37°C at the time of death.

1c
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4 marks

The image below shows part of Lindow Man, the preserved remains of a man found in Cheshire, UK in 1984.

lindow-man-1

Photograph by Mike Peel (www.mikepeel.net)., CC BY-SA 4.0, via Wikimedia Commons

It is thought that Lindow Man was a man in his 20s who lived at around the date of 100 A.D. He was found in a peat bog during commercial cutting of peat for sale as a fuel and as a compost ingredient. 

(i)
State two conditions present in a peat bog that allow the remains of bodies like that of Lindow Man to be well preserved for centuries. 

(2)

(ii)

For each condition, you stated in part (i), give a brief explanation of how that condition assists in preserving a body. 

(2)

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2a
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4 marks

Outline the stages of rigor mortis that take place after death.

2b
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2 marks

The chart shows the variation in cellular conditions in the skeletal muscles of the thigh (quadriceps) in the immediate period following death.


39z45sJs_6-1-q2b-rigor-mortis-chart---sq

Use the chart and your knowledge to determine an estimate for the time post-mortem when rigor mortis is most evident in the quadriceps of this cadaver.

Give a reason for your estimate.

2c
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3 marks

At a much later stage after death, micro-organisms begin to play a role in decomposition.

(i)
Explain the importance of decomposition to ecosystems. 
(2)

(ii)

The diagram below shows the carbon cycle, with certain processes labelled X and Y


OAJW~AVL_6-1-q2cii---carbon-cycle---sq

Which of A - D identifies the missing processes correctly?

(1)

      Process X Process Y
  A  saprophytic respiration  respiration and exhalation
  B  anaerobic respiration  fossilisation
  C  respiration and exhalation  saprophytic respiration
  D  saprophytic respiration  anaerobic respiration

2d
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1 mark

Other than carbon dioxide, name one other carbon-containing product of decomposition that is also emitted into the atmosphere by saprophytic micro-organisms.

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3a
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3 marks

The diagram below shows stages 1 - 3 of one cycle of the polymerase chain reaction (PCR).

6-1-q3a-pcr---sq

Describe the events that are taking place during stage 1 in the diagram.

3b
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1 mark

Molecule X in the diagram shown in part (a) is a DNA primer.

State the role of a DNA primer in the polymerase chain reaction.

3c
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2 marks

Stage 3 in PCR involves an enzyme.

Explain how the enzyme is suitable for its role in PCR.

3d
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3 marks

State three applications of the polymerase chain reaction.

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4a
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2 marks

State two features that allow nucleic acids or proteins to be separated by gel electrophoresis.

4b
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3 marks

During gel electrophoresis of a sample of DNA fragments:

(i)

Identify which electrode the DNA would move towards.

Justify your answer.

(2)

(ii)

State which component of DNA gives it its charge.

(1)

4c
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1 mark

State which class of enzymes can be used to cleave DNA into fragments prior to gel electrophoresis.

4d
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3 marks

Restriction enzymes and gel electrophoresis can be used in genetic screening, to identify genes associated with a disease.

The mutation of the Beta-globin gene which gives rise to sickle-cell anaemia removes a recognition site of the restriction enzyme DdeI as shown in the diagram below.

The lengths of some fragments are shown in base pairs (bp).

6-1-q4di---sq

(i)

Deduce the size of fragment X.

(1)

(ii)

DdeI digested DNA from an individual who was a carrier for the sickle-cell beta-globin gene was analysed with gel electrophoresis as shown below.

6-1-q4dii---sq

On the diagram, draw and label the DNA fragments that would result from a normal individual.

(2)

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5a
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4 marks

Archaeologists in Herculaneum recently discovered the remains of human skeletons within a house (pictured below) that was buried under volcanic ash when Mount Vesuvius erupted during Roman times in 79 AD.

nMXU8sV3_herculaneum-skeletons

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The archaeologists were interested to know if the skeletons were from related individuals. They isolated DNA from the skeletons and used it in the Polymerase Chain Reaction (PCR).

PCR utilises multiple cycles of three simple steps.

Describe these steps and explain why the researchers used PCR in their investigation.

5b
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3 marks

DNA profiling was carried out on the PCR products to identify if the skeletons came from related individuals.

The results are seen in the image below.

6-1-q5b---dna-profile---sq

It was determined that the three children were siblings and shared the same biological parents. Their mother is Adult B.

(i)

Predict which adult is the children’s father.

Justify your answer.

(2)

(ii)

Explain why the profiles for Child 1 and Child 2 are the same.

(1)

5c
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6 marks

Outline the method by which DNA profiling is undertaken and describe why it is a useful technique.

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