Biology Unit 4 Edexcel A2

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UNIT 4/TOPIC 6- ESTIMATING TIME OF DEATH:
1- Body temperature:
-All mammals produce heat from metabolic reactions, so scientist know that the core temp. of humans is around 37°C.
- From the TOD metabolic reactions slow down and eventually stop, causing body temp. to fall until it equals its surroundings- this is called algor mortis.
- Forensic scientist know that human bodies cool at a rate of 15°C to 20°C per hour, so from the temp. of a dead body they can work out the approximate TOD.
- Conditions such as air temp. clothing and body weight can effect the cooling rate of a body.

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UNIT 4/TOPIC 6- ESTIMATING TIME OF DEATH:
2-Degree of muscle contraction:
-About 4-6 hours after death, the muscles in a dead body start to contract and become stiff - this is rigor mortis.
1- rigor mortis begins when muscle cells are deprived of oxygen.
2- respiration still takes place in the muscle cells but its anaerobic, which causes a build up of lactic acid in the muscle.
3- cell pH decreases due to lactic acid therefore enzymes cannot produce ATP.
4- therefore bonds in the muscle cell become fixed and the body stiffens.
-smaller muscles in the head contract first & larger muscles in the lower body contract last- rigor mortis is effected by temp & degree of muscle development.

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UNIT 4/ TOPIC 6- ESTIMATING TIME OF DEATH:
3-Forensic entomology:
-when someone dies the body is colonised by a variety of different insects- study of this is called forensic entomology.
- TOD can be estimated by identifying the type of insect present on the body- flies are usually first & beetles at later stage.
- TOD can also be estimated by identifying stage of life cycle the insect is in
- Different conditions affect insect life cycle e.g. drugs, humidity, oxygen & temp.

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