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Question 1

what are decomposers

Answer 1

-they are microorganisms which are bacteria or fungi that break down dead organisms
- they secret enzyme that break down large substances into smaller substances and release waste products

Question 2

state the steps of carbon cycle

Answer 2

1- decomposers produce carbon dioxide and methane which is released into the atmosphere
2- plants absorb the carbon dioxide in the atmosphere and fix the carbon into carbohydrates during photosynthesis

Question 3

how can DNA profiles be created

Answer 3

• isolating a sample of DNA ex. saliva, skin, hair or blood
• producing more copies of DNA using the polymerase chain reaction (PCR)
• carrying out gel electrophoresis on the copies of DNA
• analyse the bands of DNA

Question 4

what is PCR and where is it carried out

Answer 4

• it is described as an method of DNA replication
• DNA amplification is when PCR produces many copies of of a piece of DNA
• the process is carried out in a thermal cycler which provides the optimal temperature for each stage and controls the length of time spent at each stage

Question 5

what does each PCR reaction require

Answer 5

• DNA or RNA to be amplified
• primers
  -DNA polymerase
• free nucleotides which enables the construction of new DNA or RNA
• buffer solution ensure the optimum pH

Question 6

what are the three main stages of the PCR reaction

Answer 6

• Denaturation
  
  • the double-stranded DNA is
    heated at high temperature to
    break the hydrogen bond that
    holds the two strands
• Annealing
  
  • the temperature is decreased for the primers to anneal to the ends of the strand
• Extension
• the temperature is increased to 72 °C since its the optimum temp. for taq
  at the end a single PCR cycle is completed

Question 7

what happens after PCR

Answer 7

DNA is treated with
- restriction endonuclease enzyme and fluorescent tag are added for gel electrophoresis
* restriction endonuclease enzymes break down the DNA strand into fragments of different length
* fluorescent tag enables the DNA to be seen under UV light

Question 8

what is gel electrophoresis

Answer 8

its a technique used to analyse the fragments of DNA

Question 9

how is gel electrophoresis proceeded

Answer 9

• the fragments are inserted at the far end of an agar gel
• when a current is passed through DNA is negatively charged due to the phosphate group so when placed in a electric field molecules will move towards the anode
• molecules are separated due to sizes which will move at different rate, the smaller the masses the faster they move
• Probes are added, after when the UV light is shone onto the paper producing a pattern of bands to be compared to the control
• probes are a single-stranded DNA sequences that are complementary to the regions of interest

Question 10

what is VNTR

Answer 10

• restriction endonuclease enzyme cuts the sections of repeated DNA bases known as variable number tandem repeats (VNTRs)
• the fragments will differ in length due to different number of repeats in the VNTR

Question 11

how is the DNA profile used to compare

Answer 11

• the DNA profile of a control is compared with different DNA profiles
• the more the bands that match between individuals the greater the genetic similarity
• the greater the number of VNTR examined the more reliable

Question 12

when can DNA profiling be used

Answer 12

• can be used in selective or captive breeding programmers to breed organisms that are not closely related
• when breeding with closely related genes its called inbreeding which leads small gene pool

Question 13

what is a forensics

Answer 13

• its the use of science to investigate criminal activities which involves determining the time of death(TOD)

Question 14

what are the factors that are needed to be established to determine the time of death

Answer 14

• extent of decomposition
• stage of succession
• Forensic entomology ( the study of insects)
• body temperature of the deceased
• the degree of muscle contraction

Question 15

How does the extent of decomposition establish TOD and what are the factors that affect the decomposition

Answer 15

By looking at the appearance of a body it’s seen that:
- decomposers break down cells and tissue, the skin colour can indicate TOD which will often appear green at this stage
- the decomposers will break down tissues of the organs which will produce gases such as methane and will lead to bloating, the skin will blister and fall off
- the process will continue until only the skeleton remains
- after a few decades or centuries the skeleton will disintegrate until nothing remains
- the decomposition will be affected by factors such as temperature and oxygen, the decomposition would be slower at anearobic conditions

Question 16

what is the stage of succession in death

Answer 16

• succession is known that the type of organisms will be changing overtime while in death all new arriving organisms will stay

Question 17

How does the stage of succession help to estimate TOD

Answer 17

• the bacteria will immediately after TOD be found in and on the body
• decomposers will create ideal conditions for flies to lay eggs and their larvea to hatch
• as more soft tissue is consumed by the fly larvae it creates a new condition for beetles to establish
• when the tissues dry out the flies will leave the body as they prefer moist conditions but beetles will remain and will decompose dry tissues until the body is completely decomposed
• the succession stages will differ depending on where the body is located: buried in soil, burried in coffin or under water

Question 18

How does Forensic entomology help to determine TOD

Answer 18

• a dead body provides an ideal habitat for many species of insect where they will colonise the body at different times after death
• insects can provide information from stage life cycle:
  *Larvae hatch after 24 hours, other insects have longer life cycles

Question 19

What are the factors that might affect the progression of insect life cycle

Answer 19

• drugs that may be present in the body
• humidity of the surroundings
• oxygen availability
• temperature

Question 20

how does body temperature help to determine TOD

Answer 20

• metabolic reactions provide heat when a stop person dies the metabolic reactions will stop so the temperature of the body will drop until it reaches the temperature of the surroundings this is known as algor mortis
• body temperature decreases by 1.5-2.0 °C per hour

Question 21

what are the conditions that affect the rate at which body heat is lost

Answer 21

• air temperature
• surface area : volume ratio
• presence of clothing
• percentage body fat

Question 22

what happens to the muscles after death and how does it help to determine TOD

Answer 22

• rigor mortis occurs which is when the muscles will start to contract after 4-6 hours of death which will become stiff

Question 23

how does rigor mortis come

Answer 23

• no more oxygen will reach the body which will cause the muscle to respire anaerobically which produce lactic acid
• the increase of the production of lactic acid will cause the pH to decrease and denature the enzymes that produce ATP
• without ATP the protein filaments wont be able to detach or to bind which leads to locking contraction of the muscle
• the process is affected by the level of the muscles and the temperature of the surrounding the higher the temperature the higher the rate of rigor mortis

Question 24

how do muscles contract

Answer 24

• the contraction of muscles occurs due to two protein called:
• myosin
• actin
• myosin will bind to actin which causes it to bend
• ATP is required to detach the proteins