topic 6

Question 1

factors that enable us to determine time of death

Answer 1

• state of decomposition
• forensic entomology
• body temperature
• state of rigour mortis (degree of muscle contraction)
• stage of succession

Question 2

define decomposition

Answer 2

• process in which biological molecules in dead material and waste products are digested, producing carbon dioxide, water and inorganic ions

Question 3

decomposition steps

Answer 3

• cells and tissues are broken down over course of few days. skin colour often appears greenish.
• the next stage involves breakdown of tissues and organs by micro-organisms (few days or weeks). this produces gases such as methane which leads to bloating. the skin blisters and falls off the rest of the body
• a few weeks after death, the remains of soft tissues will turn to liquid, which becomes visible as it leaves the body
• process continues over months or years till only skeleton remains, and then over few decades or centuries it disintegrates till nothing remains

Question 4

stages of succesion of dead body above ground

Answer 4

• bacteria is found in and on the dead body immediately after TOD
• as tissue decomp sets in, ideal condition for flies to lay eggs and larvae to hatch r created
• larvae fly consume more soft tissue, so favourable conditions for beetles r established
• when tissue dries out over time, flies leave body as they prefer moisture rich environment
• beetles can decompose dry tissue however, so they remain on body

Question 5

how can forensic entomology help determine TOD

Answer 5

• diff insect species colonise body at diff times after death, so provides info about TOD, eg: flies only found on body within a few hours after death, whereas beetles will only colonise body later
• also, studying the stage of life that the insect is at can also provide info: blowfly eggs hatch after 24hrs so if larvae are present on body it indicates that person died more than 24hrs ago.

Question 6

body temp and determining TOD

Answer 6

• respiration and other metabolic processes produce heat in living organisms which is necessary for maintaining our body temperature for around 37 degrees C
• when one dies, metabolic reactions eventually come to an end and since no more heat is produced, the body temp drops till it reaches temp of surrounding environment
• Body temperature decreases by 1.5-2.0 °C per hour, therefore providing forensic scientists with a way to determine the TOD based on the temperature of the body

Question 7

conditions which affect the rate at which body heat is lost

Answer 7

• air temperature
• surface area: volume ratio
• presence of clothing

Question 8

what is rigor mortis

Answer 8

• stiffening of body when muscles in body start contracting around 4-6 hours after TOD