Decay and decomposition SNAB

  • Created by: Bryan
  • Created on: 02-06-13 16:55

Decay and decomposition

  • Decay and decomposition is vital for the continuation of life on earth.
  • Plants need nutrients such as nitrogen, potassium, phosphorus and carbon to make biomass.
  • These nutrients are locked into the tissues of plants and any animals that might eat them.
  • Once the plant or animal dies the nutrients can be released only through decay.
  • The process of decomposition allows the nutrients to be recycled.
  • Micro-organisms are crucial to the decomposition process.
  • The carbon cycle is a good example of how nutrients are recycled and how micro-organisms help.
  • Bacteria and fungi produce a range of enzymes that are released onto the dead organic matter.
  • the products of external digestion are absorbed by the micro-organism and broken down in microbial respiration releasing CO2 back into the atmosphere where it can be used again for photosynthesis.
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Carbon cycle


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Time of death

It is possible to find out how long ago a mammal died, there are five main ways scientists go about this

  • Body temperature
  • Degree of muscle contraction
  • Extent of decomposition
  • Forensic entomology
  • Stage of succession
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Body Temperature

Body temperature

Body temperature is usually 37 degrees centigrade but the body begins to cool straight after death.

During the first 24 hours after death the temperature of the body when it is found can be used to work out how long ago a person died.

This can be affected by surrounding temperature, clothing, humidity and size of body (insulation)

Core temperature can be measured using an abdominal stab or a rectal temperature probe

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Degree of muscle contraction

Degree of muscle contraction

After death, muscles usually become totally relaxed and then stiffen.

This stiffening is called rigor mortis.

This usually happens 6-9 hours after death (depending on temperature).

The stiffness occurs because muscle contraction relies on ATP, which cannot be made once respiration has stopped. So the muscles become fixed.

This is due to lactic acid build up, as when a person or animal dies, aerobic respiration stops. The body tissue begins to respire anaerobically, producing lactic acid which builds up in the muscles causing them to stiffen.

The stiffness wears off again after about 36 hours in cooler conditions as the muscle tissue starts to break down

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Extent of decomposition

Extent of decomposition

Bodies usually follow a standard pattern of decay.

Enzymes in the gut start to break down the wall of the gut and then the surrounding area.

As cells die they release enzymes which help to break down tissues.

The signs of decomposition such as discolouration of the skin and gas formation combined with information about environmental conditions allow time of death to be estimated.

Interesting link: tenessee body farm research facility (google it)

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Forensic entomology

Forensic entomology

Determining the age of any insect maggots on the corpse allows the time the eggs were laid to be determined.                                

This provides an estimate of time of death assuming any eggs were laid soon after death

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Blowfly lifecycle used for forensic entomology

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Stage of succession

Stage of succession

As the body decays the populations of insects found on it change.

There is succession of species.

The community of species present when the body is found allow the stage of succession to be determined and and the time of death estimated.

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All of this information can be put together and compared with database information to give forensic scientists a very good estimate of time of death.

All methods used are subject to error and in calculation questions the answer will usually be in the form of a range of possible times rather than a precise figure

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