Topic 6: Immunity, Infection and Forensics
Forensics
Microbial Decomposition
• Microorganism such as bacteria and fungi are able to feed off and decompose dead organic
matter - they do this by secreting digestive enzymes onto the organisms.
• They digest the tissues of the dead organisms into smaller molecules, such as glucose
which is converted into carbon dioxide through respiration.
• Methane is also released from microbial decomposition.
• They play a very important role in the carbon cycle by unlocking the carbon within glucose
and other biological molecules and releasing it into the atmosphere as carbon dioxide gas.
The carbon can then be absorbed by plants, converted into glucose by photosynthesis and
used to build biological material in living organisms.
Establishing Time of Death (TOD)
When a dead body turns up under suspicious circumstances, forensic scientists will establish a time
of death (TOD). They do this by collecting data on the following factors: extent of body
decomposition, the species of insects living on the body, the body’s temperature and how stiff the
body is (degree of muscle contraction).
Extent of Body Decomposition
As soon as a living organism dies, microorganisms will release digestive enzymes which will begin
to break down the body tissues into smaller molecules. Depending on the extent of bodily
decomposition, a rough TOD can be calculated. However, abiotic conditions such as oxygen
availability and environmental temperature will affect how fast microbial decomposition occurs, so
this also needs to be factored in. Here’s a rough outline of the stages of decomposition and how these
relate to the time of death of a corpse:
• From a few hours to a few days - the skin beings to turn green as cells and tissues begin to be
broken down
• From a few days to a few weeks - methane is given off and the body becomes bloated; skin
starts to fall off
• After several weeks - tissues liquefy and leak outside of the body
• From a few months to a few years - the body tissues have been completely broken down and
only a the bones remain
, • After several decades - the bones disintegrate and nothing remains of the body
Stages of decomposition of a pig carcass.CC BY-SA 3.0,
https://commons.wikimedia.org/w/index.php?curid=115198
Forensic Entomology
Forensic entomology is the study of the insects feeding and living off a corpse. Depending on the
species that is present (and the stage of the life cycle it is in), a time of death can be estimated.
• From a few hours - flies are the first insects to appear on the body (blowflies then flesh flies).
They will start to lay eggs which take about 24 hours to hatch. This means that if larvae are
found on the body, we know that the TOD was less than 24 hours ago.
• The next insect to colonise is beetles, which eat decomposed body fat.
• A type of moth known as the pyralid moth will appear at a similar time to beetles. They will feed
on liquefied parts of the corpse as well as any clothes the body may be wearing.
• The next insect to appear is one called the cheese skipper which appears once the body’s
proteins have been digested. They feed off digested food molecules and can also feed on any
food present in the digestive system which has not been fully digested.
• One of the last insects to appear is the burying beetle, which mostly eats dead flesh.
Forensics
Microbial Decomposition
• Microorganism such as bacteria and fungi are able to feed off and decompose dead organic
matter - they do this by secreting digestive enzymes onto the organisms.
• They digest the tissues of the dead organisms into smaller molecules, such as glucose
which is converted into carbon dioxide through respiration.
• Methane is also released from microbial decomposition.
• They play a very important role in the carbon cycle by unlocking the carbon within glucose
and other biological molecules and releasing it into the atmosphere as carbon dioxide gas.
The carbon can then be absorbed by plants, converted into glucose by photosynthesis and
used to build biological material in living organisms.
Establishing Time of Death (TOD)
When a dead body turns up under suspicious circumstances, forensic scientists will establish a time
of death (TOD). They do this by collecting data on the following factors: extent of body
decomposition, the species of insects living on the body, the body’s temperature and how stiff the
body is (degree of muscle contraction).
Extent of Body Decomposition
As soon as a living organism dies, microorganisms will release digestive enzymes which will begin
to break down the body tissues into smaller molecules. Depending on the extent of bodily
decomposition, a rough TOD can be calculated. However, abiotic conditions such as oxygen
availability and environmental temperature will affect how fast microbial decomposition occurs, so
this also needs to be factored in. Here’s a rough outline of the stages of decomposition and how these
relate to the time of death of a corpse:
• From a few hours to a few days - the skin beings to turn green as cells and tissues begin to be
broken down
• From a few days to a few weeks - methane is given off and the body becomes bloated; skin
starts to fall off
• After several weeks - tissues liquefy and leak outside of the body
• From a few months to a few years - the body tissues have been completely broken down and
only a the bones remain
, • After several decades - the bones disintegrate and nothing remains of the body
Stages of decomposition of a pig carcass.CC BY-SA 3.0,
https://commons.wikimedia.org/w/index.php?curid=115198
Forensic Entomology
Forensic entomology is the study of the insects feeding and living off a corpse. Depending on the
species that is present (and the stage of the life cycle it is in), a time of death can be estimated.
• From a few hours - flies are the first insects to appear on the body (blowflies then flesh flies).
They will start to lay eggs which take about 24 hours to hatch. This means that if larvae are
found on the body, we know that the TOD was less than 24 hours ago.
• The next insect to colonise is beetles, which eat decomposed body fat.
• A type of moth known as the pyralid moth will appear at a similar time to beetles. They will feed
on liquefied parts of the corpse as well as any clothes the body may be wearing.
• The next insect to appear is one called the cheese skipper which appears once the body’s
proteins have been digested. They feed off digested food molecules and can also feed on any
food present in the digestive system which has not been fully digested.
• One of the last insects to appear is the burying beetle, which mostly eats dead flesh.
