Biology Unit 4


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Biology Unit 4
Revision Notes
Topic 6: Infection, Immunity and Forensics
20. Describe how to determine the time of death
of a mammal by examining the extent of
decomposition, stage of succession, forensic
entomology, body temperature and degree of
muscle contraction.
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 the 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
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 on to the dead organic matter. The products of external digestion are
absorbed by the micro-organism and broken down in microbial respiration, releasing carbon dioxide
back into the atmosphere where it can be used again in photosynthesis.
Forensic Entomology
Time Physical Appearance of Body Insects Present at that Stage
0-3 days Proteins and carbohydrates in the deceased body Blowflies e.g. Bluebottle flies, Syrphidae flies
begin to break down.
4-7 days Body is starting to decay and causes the abdomen Fly larvae and beetle e.g. Rove Beetles
to inflate because of the gases inside.
8-18 days Decay is well and truly setting in; the abdomen wall Ants, cockroaches, beetles and flies
begins to break down.
19-30 days The decaying body enters a stage know as Beetles and mites e.g. Springtail beetle, Acari,
'post-decay'; in wet, humid conditions, the body is Nematocera (present only during the winter
sticky and wet; in hot dry conditions, the body is months), Brachycera
dried out.
31 and over The bones, skin and hair that remain no longer give
days off a powerful stench and smell just like the soil
surrounding it.
Rigor Mortis
Temperature of body Stiffness of body Approximate time since death
Warm Not stiff Dead less than 3 hours
Warm Stiff Dead 3-8 hours
Cold Stiff Dead 8-36 hours
Cold Not stiff Dead more than 36 hours
Text Book: p. 66 - 71

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Biology Unit 4
Revision Notes
Indicator of How a forensic scientist uses the information
time of death
Body Body temperature is usually 37°C but the body begins to cool straight after death.
temperature 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 the person died.…read more


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