Forensic estimation of time of deathEdexcel International A Level Biology: Subtopic test

1. 1
   A body is found in woodland at 08:00. A pathologist measures the rectal temperature as 29.5 °C. Normal body temperature is 37.0 °C and the air temperature overnight was 12 °C. For this investigation assume that a body cools at a constant rate of about 1.5 °C per hour.

   (a)

   Which statement best explains why the temperature of a body falls after death?

   [1 mark]

   • ABlood continues to circulate and carries heat to the skin
   • BMuscles contract after death and use up heat energy
   • CRespiration stops, so no heat is produced, and heat is lost to the cooler surroundings
   • DEnzymes in the cells absorb heat from the body

   (b)

   Which factor would make the body cool more slowly than the standard rate?

   [1 mark]

   • ASeveral layers of thick clothing
   • BA strong wind blowing over the body
   • CThe body lying in a shallow stream
   • DA low air temperature

   (c)

   Calculate the minimum time since death.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A pathologist examines a body at 14:00. The eyelids and jaw are stiff, but the large leg muscles are still flexible. A second body, examined 40 hours after death, has muscles that were rigid but have become flaccid again.

   (a)

   Approximately how long after death does rigor mortis first become detectable in the small muscles of the face?

   [1 mark]

   • AWithin a few minutes
   • BAbout 12 hours
   • CAbout 36 hours
   • DAbout 2 to 4 hours

   (b)

   What causes the muscles of the second body to become flaccid again?

   [1 mark]

   • AATP is made again and the myosin heads detach
   • BMuscle proteins are broken down by enzymes, so the cross-bridges are lost
   • CThe body cools to the temperature of its surroundings
   • DCalcium ions are pumped back into the sarcoplasmic reticulum

   (c)

   Explain why the muscles become rigid after death.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A body is found in a flat in August. The room temperature was constant at 22 °C. An entomologist collects insects from the body. For the blowfly species present, the eggs hatch after 1 day at 22 °C, the larval stage lasts 5 days and the pupal stage lasts 4 days. The oldest insects found were pupae that had been in the pupal stage for 2 days. No beetles were found on the body. Blowflies lay eggs on a body within hours of death.

   (a)

   Calculate the minimum time since death and explain why your answer is a minimum.

   [3 marks]

   (b)

   Explain why the entomologist recorded the temperature in the flat and identified the insect species, and how the lack of beetles supports the estimate.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A body is discovered in an open field in summer. The abdomen had bloated and then collapsed. Much of the soft tissue had been eaten by fly larvae, most of which had left the body to pupate, and beetles that feed on dried skin and hair were beginning to arrive. The weather had been warm and dry. Blowflies are the first insects to colonise a fresh body, followed by flesh flies, and later by beetles.

   (a)

   Explain how the body decomposes, referring to enzymes, bacteria and insects.

   [6 marks]

   (b)

   Evaluate how reliable the extent of decomposition and the succession of insects are for estimating the time of death.

   [6 marks]

   Total for question 4: 12 marks

End of questions