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Question 1

Rigor mortis step 1

Answer 1

When the body dies, cells that are present in parts of the body such as the brain, which respire aerobically and don’t store much ATP or glycogen die out

Anaerobic respiration takes place and cause a build up of lactic acid in the muscle

Question 2

Rigor mortis step 2

Answer 2

Muscle cell have large stores of ATP and glycogen , and so continue relaxing and contracting until they’re permanently contracted

—> rigor mortis

Question 3

Rigor mortis step 3

Answer 3

This usually starts 2-4 hours after death, completed by 8 hours and lasts for around 36/48 hours

Question 4

Rigor mortis

Answer 4

Afterwards, the muscle relax as enzyme released from lysosome called lysozyme start to break down the tissue

Question 5

Stage of succession stage 1

Answer 5

Coloniser-

these are anaerobic bacteria that can grow rapidly in a lactic acid environment
This bacteria is released from the body itself after lysozyme breakdown the cells eg from the guts

Question 6

Stage of succession step 2

Answer 6

Blowflies

As tissue decomposition set a ideal conditions for flies to lay eggs and their larvae to hatch

They arrive within a few minute of smelling the smell that some out of the opening of the body

They lay eggs which hatch into maggots that breakdown the tissue and feed on them , liquefying soft tissue so that the adults can also feed

Question 7

Stage of succcesion step 3

Answer 7

Beetles

As more soft tissue is consumed by the fly larvae it create favourable condition for beetles to establish

They also lay their eggs however their larvae feed on their maggots rather than the body itself

Question 8

Stages of succession stage 4

Answer 8

When tissue dries out over time flies will leave the body as they prefer a moisture rich environment

Beetles however can decompose dry tissue so they will remain on the body

Once all tissues have been decomposed most organism will leave the body

They lay their egg in the fly and beetle larvae

Question 9

Stages depend on a number factor

Answer 9

1) temperature
As it rises the rate of decay will be higher because enzyme have more kinetic energy and so chemical reaction are fast

2) level of exposure
An exposed body will be more available to flies and beetles compared to one that is underground

Question 10

Forensic entomology

Answer 10

The study of insect life relating to crime .

Different insect species will colonise a body at different time after death providing information about the TOD

Scientists know how long life cycles of insect that colonise the body last based on environmental conditions

Question 11

PCR process step 1

Answer 11

Mixing DNA polymerase, primers, a good supply of 4 nucleotides and a buffer

Question 12

PCR step 2

Answer 12

The temperature is first increased to 95c break hydrogen bonds and split the DNA into single strand (denaturing)

Question 13

PCR step 3

Answer 13

The temperature is then decreased to 60c so that primers can attach (annealing)

Question 14

PCR step 4

Answer 14

The enzyme DNA polymerase then attaches complementary free nucleotides and makes a new strand to align next to each template (synthesis). The temperature is increased to 75c for this stage the optimum for the taq DNA polymerase

Question 15

What is DNA a sequencing ?

Answer 15

Analyse the entire DNA strand to find a pattern of bases that codes for a protein

Question 16

What is DNA profiling

Answer 16

Analyse introns and uses them to identify individual

Question 17

Define rigor mortis

Answer 17

Temporary muscle contraction causing the body to become rigid after death

Question 18

Rigor mortis step 1 .5

Answer 18

The pH cells decrease due to the lactic acid inhibits enzyme that produce ATP

No ATP means the bonds between the myosin and actin in the muscle cell become fixed and body stiffens

Question 19

Explain why the body of a mammal cools down after death

Answer 19

The heat of the body is produced as a result of the metabolic reaction taking place
—> respiration in active tissue such as the muscle and the brain

After death these reaction slow down and stop so no more heat energy produced

Question 20

Why is cooling rate slower in the first hour after death

Answer 20

The metabolic reaction reaction don’t stop immediately after death - many cells continue to respire contract and so on until all the available oxygen and ATP is used up

So heat continues to be generated in the first hour after death although slower rate so body temperature drops but relatively slowly

Question 21

Explain how factors such as external temperature whether the body is wet or dry and whether a body is wrapped or exposed will affect the rate of cooling after death

Answer 21

The temperature gradient between the body and the environment will affect rate of cooling, for example if someone dies inside a warm house the body will cool down more slowly than if it is on a cold windy hillside, so the external temperature and weather conditions have to be taken into consideration.

A naked body will cool much faster by convection than a clothed body, and a body wrapped in blankets or a duvet will cool down even more slowly due to insulation.
A wet body will cool faster than a dry body as a result of heat lost as the water evaporates, and death in a warm bath or beside some form of heating will also change the rate of cooling.

Even the body position affects the rate of cooling- a stretched out body has a much bigger exposed surface area to volume ratio than a curled up one and so will cool down faster.

All of these different factors have to be taken into consideration when using temperature as a guide to the time of death.

Question 22

Explain why rigor mortis alone is a limited use in determining the time of death

Answer 22

amount of ATP stored in the muscles at the time of death which depends on genetic tendency and levels of fitness
- level of activity before death – how much ATP has been used, temperature of the individual at the point of death, temperature of the surroundings
- speed at which rigor passes also depends on a variety of factors such as external temperature, activity of enzymes.

Question 23

Stage of succession

Answer 23

Immediately after the TOD conditions in a dead body are most favourable for bacteria

As bacteria decompose tissues condition in a dead body become favourable for flies and their larvae

When fly larvae feed on the dead body they make conditions favourable for beetles beetles move in

As a dead body dries out condition become less favourable for flies they leave the body. Beetles remain as they can decompose dry tissue

When no tissue remains condition are no longer favourable for most organism

Question 24

Extraction of DNA

Answer 24

Small sample of DNA is collected for genetic fingerprinting
- hair
- blood
- blood cell

If the sample is small then PCR is used to amplify the amount of DNA

Question 25

DNA digestion

Answer 25

Once the DNA is amplified and extracted the DNA is digested by cutting it into small fragments using RESTRICTIVE ENDONUCLEASES

Cut at a recognition sites leaving the VNTRs intact

Question 26

SEPARATION (gel electrophoresis) step 1

Answer 26

1) agarose gel plate is created and wells are cut into the gel at one end

2) the gel is submerged in a tank containing electrolyte solution - conducts electricity

3) DNA is transferred into the wells using a micro pipe the ensuring that a sample of DNA standard is loaded into the first well
—> the purpose of the standard is to produce a set of known results with which to compare any new results

Question 27

SEPARATION (gel electrophoresis) step 2

Answer 27

The negative electrode is connected to the end of the plate with the wells and the positive anode is connected at the far end
The DNA fragments move towards the anode due to the attraction between the negatively charged phosphates of DNA and the anode

The smaller mass / shorter pieces of DNA fragments move faster and therefore further from the wells than the larger fragments

Question 28

SEPARATION (gel electrophoresis) step3

Answer 28

Probes are then added, after which an X-ray image is taken or UV-light is shone onto the paper producing a pattern of bands which can be compared to the control, or standard, fragments of DNA
Probes are single-stranded DNA sequences that are complementary to the regions of interest; they can be
A radioactive label which causes the probes to emit radiation that makes the X-ray film go dark, creating a pattern of dark bands
A fluorescent dye which fluoresces when exposed to UV light, creating a pattern of coloured bands

Question 29

What factors does the molecules move through the agar plate

Answer 29

Molecules move through the agar due to the difference in charge across the gel
Positively charged molecules will move towards the cathode (negative pole) while negatively charged molecules will move towards the anode (positive pole)
DNA is negatively charged due to the phosphate groups and so when placed in an electric field the molecules move towards the anode

The molecules are separated according to their size / mass
Different sized molecules move through the gel at different rates
The tiny pores in the gel allow smaller molecules to move quickly, whereas larger molecules move more slowly

Question 30

Analysing the results of gel electrophoresis

Answer 30

VNTRs are known as micro- or mini-satellites depending on the number of repeats that occur; micro-satellites have fewer repeats than mini-satellites
Different people have different numbers of repeats in their VNTR regions, so the fragments will differ in length depending on whether there are few or many repeats
Different individuals will have different lengths of DNA fragments, so a different pattern of banding will form on each profile
Every banding pattern will be unique to an individual, so comparisons of DNA from crime scenes with that of suspects is a reliable way of finding out who was present at a crime scene

Question 31

Paternity test

Answer 31

DNA profiles can be used to determine the genetic relationships between people, e.g. in paternity tests
During a paternity test the DNA profile of a child is compared with a variety of candidates that could be the potential father
If many bands of the child’s DNA profile match with the bands in a paternity candidate’s profile, this could indicate that they are the most likely biological father
During fertilisation half of the DNA comes from each parent, so a child will share half of their DNA with a parent
When comparing DNA profiles the more bands that match between the profiles, the greater the genetic similarity between those individuals and the closer the relationship

Question 32

VNTR

Answer 32

DNA profiling is a useful tool in forensic science where it can be used to link possible suspects to a crime scene
Regions of DNA, known as short tandem repeats, are examined
These short tandem repeats are a type of non-coding, repeated sequence of bases known as a variable number tandem repeat, or VNTR; short tandem repeats consist of short repeating sections, and are also known as micro-satellites
The greater the number of these regions examined, the more reliable the evidence provided
If only a few regions are analysed then there is a greater chance that closely related individuals will have an identical profile; an analysis of 11 or more sites is considered to be reliable evidence in a law court

Question 33

Hybridisation

Answer 33

DNA probe - short single stranded pieces of DNA complementary in base sequence to the VNTRs
—> the probe are fluorescently labelled

Question 34

Development

Answer 34

The agar gel will shrink and crack as it dries and therefore the VNTR and DNA probe are transferred to a nylon sheet

The nylon sheet can then be exposed to X ray to visualise the position of radioactive gene probe or UV light of fluorescent probe were used

Question 35

Suggest three reasons why the theoretical value may not be acheieved

Answer 35

Not enough nucleotide added at the start

Primers don’t anneal properly

Strands don’t separate fully

Question 36

Suggest why evidence from DNA profiles may not be conclusive

Answer 36

Identical twins have the same DNA

Closely related people have similar DNA

A large number of micro satellite sites should be compared

Question 37

What is decomposer

Answer 37

1) enzyme secreted from the cells of these organism break down biological end tissue

Question 38

Extent of decomposition step 1

Answer 38

Decomposer break down cells and tissue over the course of a few day
—> appearance of skin will often appear greenish colour

Question 39

Extent of decomposition step 2

Answer 39

Breakdown of tissue and organs by micro-organism over the course of few days or weeks
—> produce gases like methane which causes bloating
The skin will blister and fall off the rest of the body

Question 40

Extent of decomposition step 3

Answer 40

A few week after death the remain of the soft tissue will turn to liquid which becomes visible as it leaves the body
—> will continue over the course of months or year until only the skeleton remain
—> after a few decade or centuries the skeleton will disintegrate until nothing remains

Question 41

What rate of decomposition will be affected by factors

Answer 41

Temperature

Availability of oxygen

Decomposition would be slower in anaerobic condition and at lower temperature but would be faster at high temperature

Question 42

What is the difference between the ecology and forensic succession

Answer 42

The early pioneer species are out competed and disappear as the system matures while in a dead body all the of the newly arriving specie remain as decomposition progresses

Question 43

Clues

Answer 43

Another clue that insects can provide is the stage of life cycle they are at
E.g. blowfly eggs will hatch after about 24 hours so if larvae are present on the body it indicates that the person died more than 24 hours ago
Other insects have longer life cycles, so if only blowfly larvae are found it indicates that only 24 hours has passed since TOD
Factors that might affect the progression of insect life cycles include
Drugs that may be present in the body
Humidity of the surroundings
Oxygen availability
Temperature

Question 44

How can DNA profiling be useful for plants

Answer 44

DNA profiling can also be useful in selective or captive breeding programmes of animals or cultivation of plants
DNA profiles of the particular organisms can be compared to determine which are genetically the most different from each other
These organisms will then be crossbred, ensuring that the individuals that breed together are not closely related
Breeding between closely related individuals is known as inbreeding, and can cause genetic problems at an individual and population level
In individuals there can be an accumulation of harmful recessive alleles that might otherwise have been masked by healthy dominant alleles
Inbreeding leads to a smaller gene pool within a population, which can reduce a population’s ability to adapt to change

Question 45

Factors affecting rigor mortis

Answer 45

Amount of ATP left in the muscle

Temperature- higher temperature increase the rate of rigor mortis

Question 46

Condition for recycling nutrients

Answer 46

Warm and moist

High temperature
—> they will have greater enzyme activity
—> not too high because they will denaturation

Moist
—> easier to dissolve their food and prevent from drying completely

Available of oxygen
—> decay faster