Topic 6A: Microbial Decomposition And Time Of Death

Question 1

Why do microorganisms have to decompose organic matter?

Answer 1

To continue the carbon cycle

Question 2

What do the microorganisms inside and outside an animal do when they die?(4)

Answer 2

– Secrete enzymes

– That decompose dead organic matter.

– Into small molecules that they can respire

– Causing small molecules of methane and carbon dioxide is to be released into the atmosphere

Question 3

What are the five factors used to determine the time of death of a body?

Answer 3

– Body temperature

– Degree of muscle contraction

– Forensics entomology

– Extent of decomposition

– Stage of succession

Question 4

Why can’t one factor be used to determine the time of death of the body?

Answer 4

On their own the factors aren’t accurate enough

Question 5

How is body temperature used to determine the time of death of a body?(4)

Answer 5

– Metabolic reactions produce heat

– From TOD metabolic reactions slowdown eventually stop

– Causing body temperature to fall until equals temperature of surroundings (algor mortis)

-forensics scientist no that’s human body is cool at a rate of 1.5°C per hour. Therefore they can approximate the time of death

Question 6

Why might using the factor of body temperature alone not be enough to accurately determine the TOD?

Answer 6

Conditions such as air temperature, clothing and body weight can affect the cooling rate of a body

Question 7

What is algor mortis?

Answer 7

– Decomposition process where body temperature falls until it equals the temperature of its surroundings

Question 8

How is degree of muscle contraction used to determine TOD?(3)

Answer 8

• usually takes around 12 to 18 hours after time of death for every muscle in the body to contract
• Rigor mortis wears off around 24 to 36 hours after the TOD

– Degree of muscle contraction is compares to this

Question 9

What is rigor mortis?(2)

Answer 9

– When the muscles in a dead body start to contract and become stiff

– Begins when muscle cells become deprived of oxygen

Question 10

Explain the process of rigor mortis(4)

Answer 10

– Begins when muscle cells become deprived of oxygen

– Respiration takes place anaerobically in muscle cells causing a buildup of lactic acid

– PH of cells decrease due to lactic acid inhibiting enzymes that produce ATP

– No ATP means bonds between myosin and actin in muscle cells become fixed and body stiffens

Question 11

What is the order of muscle contraction after the time of death?(2)

Answer 11

– Small muscles in the head contract first

– Larger muscles in lower body contract last

Question 12

What is forensics entomology?

Answer 12

The study of different insects which colonise a body after it has died

Question 13

How is forensics entomology used to determine the time of death?(2)

Answer 13

– Can be estimated by identifying the type of insect present on the body

– Can be estimated by identifying the stage of life cycle the insect is in

Question 14

Why might forensic entomology not be enough to accurately determine TOD?(2)

Answer 14

• Different conditions will affect an insects life cycle

- such as drugs, humidity, oxygen and rtemperature

Question 15

How is the extent of decomposition used to determine the time of death?(2)

Answer 15

• Immediately after death bacteria and enzymes begin to decompose body, altering appearance
• Extent of decomposition is compared to TOD

Question 16

Why isn’t extent of decomposition accurate enough to be used alone to determine TOD?

Answer 16

Different conditions can affed rate of decomposition such as temperature, oxygen availability etc

Question 17

How is the stage of succession used to establish TOD?

Answer 17

• Type of organisms found on dead body change over time

- TOD from the particular change of succession

Question 18

Explain the stages of succession occurring on a body left to decompose above ground?(5)

Answer 18

• Immediately after TOD conditions in a dead body are most favourable for bacteria
• as bacteria decompose tissue conditions become favourable for flies and larvae
• larvae fly feed on dead body making conditions favourable for beetles
• as body dries out, conditions are less favourable for flies and more favourable for beetle which remain and can decay dead tissue
• with no remaining tissue, conditions no longer favourable for most organisms

Question 19

What is is the difference between plant succession and succession on dead body?

Answer 19

Most of early insects remain as other insects colonise for succession on a body

Question 20

What can affect the stage of succession of a body?

Answer 20

Location i.e.body is above or ender ground