Topic 6A : Forensics

Question 1

how do microorganisms decompose organic matter

Answer 1

when plants and animals die, microorganisms on and in them secrete enzymes that decompose the dead organic matter into small molecules they can respire

Question 2

what is released when microorganisms respire

Answer 2

methane, carbon dioxide

Question 3

which five factors are used to determine the time of death of a mammal

Answer 3

extent of decomposition

stage of succession

forensic entomology

body temperature

degree of muscle contraction

Question 4

forensics

Answer 4

the use of science in the investigation of criminal activities

it involves the collection and analysis of evidence from potential crime scene

Question 5

describe the stages of decomposition

Answer 5

hours to a few days : cells/tissues are broken down by the body’s enzymes and bacteria that were present before death

few days to a few weeks : microorganisms decompose tissues and organs which produces gases causing the body to become bloated and the skin begins to blister and fall off

few weeks : tissues begin to liquefy and seep out into the area around the body

months to years : skeleton remains

decades to centuries : skeleton beings to disintegrate until nothing left

Question 6

how is extent of decomposition used to determine time of death

Answer 6

bodies in similar environmental conditions show regular patterns of decay

Question 7

what factors affect extent of decomposition

Answer 7

mild heat increases rate as enzyme activity increases

intense heat decreases rate as enzymes
become denatured

humidity : the more humid the quicker

presence of wounds increases rate as bacteria are able to enter more easily

Question 8

normal human body temperature

Answer 8

between 36.5 and 37.5

Question 9

how can the body temperature of a corpse be measured

Answer 9

rectally or by measuring liver temperature

Question 10

what is the rate at which the body temperature decreases after death

Answer 10

1.5 to 2 degrees every hour

Question 11

factors affecting cooling rate of body after death

Answer 11

air temperature, clothing and body weight

Question 12

algor mortis

Answer 12

metabolic reactions slowing down and eventually stopping causing body temperature to fall until its equal to the temperature of surroundings

Question 13

rigor mortis

Answer 13

the stiffening of body caused by muscles contracting 4-6 hours after death.

Question 14

what causes rigor mortis

Answer 14

anaerobic respiration occurs due to no oxygen leading to a build up of lactic acid

lactic acid decreases pH of cells which inhibits the enzymes producing ATP

without ATP the myosin head cant be release from actin filaments locking the muscles in contracted state

Question 15

explain the sequence of events happening during rigor mortis

Answer 15

2-6 hours : eyelids, jaw and small muscles stiffen

8-11 hours : centre of the body stiffens

12 hours : entire body rigid

15-36 hours : slow loss of rigor, small muscles in the head and neck first

36-48 hours : rigor disappears and muscles become relaxed

Question 16

forensic entomology

Answer 16

the colonisation of a death body by variety of different insects

Question 17

how can forensic entomology help determine how long a body has been dead

Answer 17

it identifies the type of insect present and the stages of life cycle the insects are in

Question 18

what affects an insect’s life cycle

Answer 18

drugs, humidity, oxygen and temperature

Question 19

succession

Answer 19

the change in types of organism found in a dead body

Question 20

describe the stages of succession

Answer 20

immediately after death, bacteria decomposes tissues due to favourable conditions which creates favourable conditions for flies and their larvae.

fly larvae feed on dead body making conditions favourable for beetles.

body dries out making conditions less favourable for flies so they leave the body (beetles remain and decompose dry tissue).

no tissue remain making conditions not favourable for most organisms.

Question 21

what factor affects stages of succession

Answer 21

location of the body

Question 22

how can stages of succession be used to determine time of death

Answer 22

as body decays, species colonising the body change

as there is a predictable sequence of ecological succession, analysis of the community of species present can be used to determine time of death.

Question 23

what is the purpose of DNA profiling

Answer 23

genetic identification of people

determine genetic relationships between humans, animals and plants

to identify an individuals risk of developing particular diseases

Question 24

how is DNA profile created

Answer 24

DNA sample obtained

polymerase chain reaction to amplify the DNA

a fluorescent tag is added

gel electrophoresis used to separate DNA

gel viewed under UV light

Question 25

purpose of polymerase chain reaction

Answer 25

makes millions of copies of specific regions of the DNA so there are enough to make a DNA profile

Question 26

outline the stages of polymerase chain reaction

Answer 26

reaction mixture set up containing DNA sample, free nucleotides, primers and Taq polymerase

mixture heated to 95 degrees to break hydrogen bonds between two strands of DNA in a thermal cycler

mixture cooled between 50 and 55 degrees so primers can bind (anneal) to strands (to outcompete the DNA as DNA would want to join back)

reaction mixture heated to 72 degrees so Taq polymerase can work and it lines up free nucleotides alongside each template strands, complementary base pairing occurs.

two new copies of the fragment of DNA are formed and one cycle of PCR is complete

cycle starts again, with mixture heated up to 95 degrees but this time all four strands are used as template meaning that each PCR cycle doubles the amount of DNA.

Question 27

primers

Answer 27

short pieces of DNA that are complementary to the bases at the start of the fragment you want

Question 28

DNA polymerase

Answer 28

enzyme that creates new DNA strands

Question 29

how does gel electrophoresis happen

Answer 29

restriction enzymes cut specific base sequences of DNA

place the cutted DNA in a wells of agarose with buffer

run an electrical current

DNA separates into bands and smaller DNA travels further

add fluorescent tag to visualise the DNA, UV light should also be used

more similar bands more closely related

Question 30

explain why acidic conditions in peat bogs prevent decomposition

Answer 30

such conditions inhibit or denature enzyme therefore enzymes cant digest or break down organic material