Micro bacterial Decomposition and Time of Death

How is dead organic matter decomposed?

Microorganisms secrete enzymes that decompose the dead organic matter into small molecules that they can respire

• methane and CO2 is released into the atmosphere

What are the 5 ways scientists can estimate time of death?

• Body temperature (algor mortis)

• Degree of muscle contraction (rigor mortis)

• Forensic entomology

• Extent of decomposition

• Stage of succession

How can body temperature help estimate the time of death of a body?

• all mammals produce heat from metabolic reactions (respiration)

• after the organism died, the metabolic reactions slow down and stop

• body temperature decreases to the temperature of the room

• algor mortis

• rate of decrease is 1.5-2 degrees an hour

What external factors can affect the cooling rate of a body?

• air temperature

• clothing (insulated?)

• body weight (thinner people decrease in temperature faster)

How can the degree of muscle contraction help estimate the time of death of a body?

• after 4-6 hours the muscles in a dead body will start to contract and stiffen

• rigor mortis

• muscle cells have no oxygen

• anaerobic respiration builds up lactic acid in muscle

• pH of cell decreases and denature enzymes that produce ATP

• no ATP = myosin doesn’t have any ATP to release itself from actin filaments in muscle cells and becomes fixed

• body is stiff

In what order do muscle cells stiffen?

• small muscles (in the head) contract first

• larger muscles are last to contract

• 4-6 hours body starts stiffening

• 12-18 hours whole body is stiff

• 24-36 hours wears off

How can forensic entomology help estimate the time of death?

• when a body died insects quickly colonise

• entomology is the study of insects

• the type of insect can indicate how long it has been since the time of death

• the stage of life cycle of certain insects can also help

What order do insect colonise a dead body?

• few hours - flies first to appear

• blowflies lay eggs and they hatch 24hours after being laid

• if the body has larvae eggs still intact it has not been more than 24 hours since time of death

• later - beetles

What affects the life cycle of an insect on a dead body?

• drugs

• humidity

• oxygen

• temperature (higher temp higher rate of metabolism)

How can the extent of decomposition help estimate the time of death?

• after death bacteria and enzymes immediately start to decompose the body

hours - few days

• cells and tissues break down by body enzymes and body bacteria

• skin turns green

few days - few weeks

• microorganisms decompose tissues and organs

• gases like methane produced - body becomes bloated

• skin blisters and falls off

a few weeks

• tissues liquefy and seep into the area around the body

few months to few years

• only skeleton remains

decades to centuries

• skeleton disintegrates until nothing remain

What affects the rate of decomposition?

• temperature

• oxygen availability (aerobic microorganisms need oxygen to respire)

How can the stage of succession help estimate the time fo death?

• the types of organisms found in dead bodies changes over time going through stages succession

above ground:

• immediately after body dies it is the ideal conditions for bacteria

• bacteria decompose tissues

• body conditions ideal for flies and larvae

• fly larvae feed on dead body

• body conditions become ideal for beetles

• beetle move in

• body eventually dries and conditions less ideal for flies so they leave

• beetles stay and decompose dry tissue

• when there is no more tissues left the body condition is not favourable for most organisms

What are the differences between succession on a dead body and plant succession?

most of the early insects remain on the body as other insects colonise it

What can affect the progress in the stages of succession ?

location of the body (above the ground, underground, under water, sealed)