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How to use the extent of decomposition in order to determine a time of death.
Autolysis - tissues break down due to the actions of enzymes
Putrefaction begins - skin turns green around abdomen reddish-green → purplish black
Bacteria causes gas + liquid bubbles → bloating
bloating passes - liquified tissues seep out of body + body dries out
How to use stage of succession for TOD
immediately after conditions are optimum for bacteria
bacteria decompose tissue → favourable for flies and larvae
fly larvae feed on body → favourable for beetles
body dries → less fav for flies, beetles stay to decompose dry tissue
no tissue=not favourable for most
How can forensic entomology be used to determine the time of death.
TOD cane be estimated by the life cycle of the insect
blowfly larvae hatch from eggs about 24 hours after being laid
If only eggs are found on a body you could estimate a TOD no more than 24 hours.
Different conditions will affect an insects life cycle.
How is body temperature used to determine a TOD.
From TOD metabolic reactions slow down and eventually stop
Temperature falls + equals surroundings=Algor mortis
Human bodies cool at around 1.5-2.0°C /hr
Conditions such as: air temperature, clothing and body weight affect temperature.
How can degree of muscle contraction be used to determine TOD.
about 4-6 hours after death the body stiffens=rigor mortis
respiration still takes place in the cell buts its anaerobic → lactic acid buildup
pH decreases → inhibits enzymes that produce ATP
No ATP means bonds in muscle cells fix and body stiffens.
smaller muscles first + is faster at higher temp
What’s the role of micro-organisms in the decomposition of organic matter and the recycling of carbon.
Important part of the carbon cycle
microorganisms on+in the body secrete enzymes that decompose dead organic matter int o small molecules they can respire
Methane and Co2 are released→ recycles carbon back to atmosphere.
How is DNA profiling used for identification and determining genetic relationships between organisms
A DNA profile is a fingerprint of someone’s DNA
Everyone’s DNA is different therefore everyone’s DNA profile is unique
How can DNA be amplified using PCR
The DNA mixture is heated to 95°C → break hydrogen bonds between the strands
Mixture cooled 65°C so primers can anneal to the strands (primers start signal where to start synthesising the DNA
heated to 72°C so polymerase can work (lines up+ complementary base pairing)
Two new copies are formed+1 cycle complete
Cycle restarts and strands double each time.
Where are virus’s genetic material stored
They contain a core of nucleic acid which is either DNA or RNA
What are attachment proteins?
They stick out from the virus’s capsid and allow it to cling on to a host cell
What is an envelope?
An extra outer layer stolen from the previous host cell.
What is the capsid
The protein coat surrounding the core
Compare the structures of bacteria and viruses
Bacteria are single celled whilst viruses are non cellular particles
both have no nucleus
both can cause disease
bacteria reproduce by binary fission, viruses invade host cells
Explain the role of DNA primers in the production of the amplified 345bp sequence (2)
Primers have a specific base sequence
Bind to complementary bases
Therefore providing a site for DNA polymerase
Explain why the amplified DNA fragments for the G20210A allele and the wild type allele are different (3)
The restriction enzyme cuts at a specific site
that is only present in the G20210A allele
therefore a shorter fragment is produced for G20210A
Devise an investigation to determine the optimum number of cycles for the polymerase chain reaction used to amplify the DNA for this test.
Make the mixture, DNA polymerase added in excess
Control the temperature
change the number of cycles
use gel electrophoresis to determine amount of DNA produced
choose the smallest number of cycles that produce a band
Describe a study for the changes in insect species on a body after death with pigs (3)
Control variable: same mass/size/age
Temperature monitored to make sure its the same
record the presence of different species every 24 hours
Explain how the results of a pig study could be used to help establish the TOD of a human (insects) (3)
Record which insects are present on the human and compare with the results of the pig
Take into account which stages of the life cycle are present
When using stage of succession to determine TOD environmental variables need to be taken into account
Explain the effect of ambient temperature on the rate of decomposition (3)
The higher the ambient temperature the higher the rate of decomposition
Enzymes in bacteria will have more kinetic energy and decompose faster
Increases growth rate of bacteria/fungi
Note
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