Time of death and decompositionEdexcel A-Level Biology A: Subtopic test

1. 1
   A body is found in a room in a house at 10:00. The room temperature is 18 °C. The rectal temperature of the body is 31.0 °C. The pathologist records that rigor mortis is present in the muscles of the jaw, neck and arms but not yet in the legs. For this question, assume that the body temperature was 37.0 °C at death and that the body has cooled at a constant 1.5 °C per hour.

   (a)

   Why do muscles become rigid after death?

   [1 mark]

   • ALysosomal enzymes digest the muscle proteins immediately.
   • BATP is no longer made, so myosin heads cannot detach from actin and the muscle stays contracted.
   • CActin filaments dissolve, so the muscle fibres shorten permanently.
   • DCalcium ions cannot be released, so cross-bridges form that cannot be broken.

   (b)

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

   [1 mark]

   • AThe body is wrapped in a thick duvet.
   • BThe body is in a draught from an open window.
   • CThe body has a very small mass compared with its surface area.
   • DThe body is lying in a bath of cold water.

   (c)

   Calculate the time that has passed between death and the discovery of the body. Show your working.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A body is found in woodland in June. Blowfly larvae are present and the largest are 14 mm long. No pupae are present. Laboratory data show that at 18 °C, the mean temperature recorded at the site, blowfly eggs laid on a body hatch after about 1 day and the larvae reach 14 mm in length 5 days after the eggs were laid.

   (a)

   Why are blowflies usually the first insects to arrive at a dead body?

   [1 mark]

   • AThey feed on tissue that has already been broken down by beetles.
   • BThey are attracted only when the body has been reduced to a skeleton.
   • CTheir larvae feed on dry skin and bone.
   • DThey detect the chemicals released as the body starts to decompose and lay eggs within hours of death.

   (b)

   Why does the entomologist need the temperature record from the site?

   [1 mark]

   • ATemperature decides which species of blowfly is attracted to the body.
   • BBlowfly larvae can only survive above 18 °C.
   • CThe rate of larval development depends on temperature because development is controlled by enzymes.
   • DTemperature determines how many eggs are laid on the body.

   (c)

   Estimate the minimum time since death and explain your answer.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   At a forensic research facility, a team observes a human donor body left on the surface of woodland soil in summer. Decomposition passes through stages: fresh (0–3 days), bloat (4–7 days), active decay (8–15 days), advanced decay (16–30 days) and dry remains (over 30 days). Blowflies are the first insects to arrive, followed in turn by flesh flies, then carrion beetles during active decay, and finally hide beetles and mites on the dry remains.

   (a)

   Explain how the stage of succession on a body found in similar woodland could be used to estimate the time of death.

   [3 marks]

   (b)

   A second body is found in the same woodland in winter. Explain how its extent of decomposition would differ from that of a summer body of the same age, and how this could affect an estimate of the time of death.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A body is found in woodland in late spring. It is badly decomposed: the soft tissues are partly liquefied, the skin is peeling away, blowfly larvae of several different sizes are present and fungal growth covers some of the clothing. The body is cold, there is no rigor mortis, and the rectal temperature is the same as that of the surrounding soil. The police do not know when the person disappeared.

   (a)

   Explain how micro-organisms decompose the body and how the carbon in the body is recycled.

   [6 marks]

   (b)

   Evaluate how useful body temperature, degree of muscle contraction and forensic entomology are for estimating the time of death in this case.

   [6 marks]

   Total for question 4: 12 marks

End of questions