Forensics, Immunity And Infection

Question 1

Explain the role of DNA primers in PCR

Answer 1

Have a specific base sequence
Bind to complementary bases of the DNA to be amplified
So they provide a site for the DNA polymerase to bind

Question 2

Explain why the amplified DNA fragments for 2 alleles are different

Answer 2

Base sequences of the alleles are different
Restriction enzyme cuts at a specific site
That is only present in one allele

Question 3

Devise an experiment to determine the optimal number of cycles for PCR to amplify DNA

Answer 3

Need DNA, polymerase, primers, mononucleotides
Control temp at diff stages: 95, 55, 70
Change number of cycles
Use gel electrophoresis to determine quantity of DNA produced
Choose smallest number of cycles that produces an observable band

Question 4

body farms use the bodies of pigs to study the changes in insect species on a body after death
describe how this study could be carried out

Answer 4

standardisation of pigs studied eg same size/ breed/ mass/ age/ sex
control temp
record presence of diff species of insects
at regular time intervals eg every 24 h

Question 5

describe how DNA profiling could be carried out to show that snakes are diff species

Answer 5

DNA obtained from 2 types of snake

restriction enzymes used to produce fragments of DNA

gel electrophoresis used to analyse DNA samples and separate fragments

more differences in pattern of bands produced indicated that the snakes are different species

Question 6

describe the changes that occur inside the body un the first week after death

Answer 6

body temp falls
rigor mortis
break down of cells by enzymes in the body
discolouration/ bloating

Question 7

describe the role of decomposers in the carbon cycle

Answer 7

break down organic material from the dead body
respire
releasing CO2

Question 8

explain the effect on temp on the rate of growth of insects on the dead body

Answer 8

temp affects enzymes
an increase in temp increases kinetic energy
producing more frequent collisions between enzyme and substrate molecules

Question 9

devise a procedure using gel electrophoresis to compare amplified DNA

Answer 9

restriction enzymes used to cut DNA into fragments
DNA samples loaded onto agarose gel
potential difference applied across gel
fluorescent dyes added to visualise bands
the position of the bands produced can be compared

Question 10

explain the affect of ambient temperature on the rate of decomposition

Answer 10

increase in temp increases rate of decomposition
increases enzyme activity
increases growth rate of bacteria/ fungi/ decomposers

Question 11

describe how one PCR cycle would increase the quantity of DNA present

Answer 11

heat to 95º to break H bonds between DNA strands
joining of primers/ annealing at 55º
addition of nucleotides, DNA polymerase involved in formation of phosphodiester bonds
to double the quantity of DNA

Question 12

describe the infection control practices that hospitals have introduced

Answer 12

hand wash stations

docs/ nurses not to wear ties/ long sleeves/ watches

testing patients for presence of antibiotic resistant bacteria before admission and quarantine of infected patients

increased disinfection of surfaces

Question 13

explain how changes in the blood vessels result in the redness and swelling seen at the site of inflammation

Answer 13

histamine released
causes vasodilation
increases blood flow to site, causing redness
also causes permeability of caps to increase
allowing plasma to leave caps, causing swelling

Question 14

describe how HIV particles are able to enter T helper cells

Answer 14

GP120 on surface of the virus

bind to CD4 receptors on surface of T helper cells

viral envelope fuses w membrane of T helper cell

viral RNA enters the cell

Question 15

explain why the destruction of T helper cells causes the symptoms of AIDS

Answer 15

reduces cytokine production

reducing cloning/ activation of B cells

reducing antibody production

increased risk of opportunistic infections

Question 16

which cell produces antibodies

Answer 16

plasma cell

Question 17

explain why the presence of microorganisms on the skin and in the gut helps to prevent pathogenic organisms multiplying in the body

Answer 17

flora in gut and skin better adapted to conditions

therefore can outcompete pathogenic organisms

bacteria in the gut secrete chemicals/ lactic acid which help to destroy pathogens

Question 18

explain the role of the T cells in the body of a person who becomes infected with a virus that they got vaccinated for

Answer 18

a vaccinated person will have T memory cells

recognise specific antigens

T helper cells that activate B cells/ T killer cells

T killer cells destroy cells infected with virus

Question 19

explain why there are relatively few species of bacteria in the stomach

Answer 19

pH in stomach is too low for enzymes of most bac to function

bac that live in the stomach have adaptations that enable them to survive

Question 20

state what is meant by the term bacteriostatic antibiotic

Answer 20

a substance which can inhibit the growth/ prevent multiplication of bacteria

Question 21

what type of chemical reaction takes place in decomposition

Answer 21

hydrolysis

Question 22

why is there a decrease in mass during decomposition

Answer 22

decomposers release enzymes for decomposition

monomers formed that are soluble and soak into ground/ taken up by organisms

respiration of glucose by decomposers

CO2 released

Question 23

explain what effect an increase in temperature would have on the rate of decomposition

Answer 23

increase rate

increased kinetic energy increases number of collisions and enzyme- substate complexes formed

above a certain temp, rate of decomposition would decrease/ stop

enzymes become denatured

Question 24

suggest 2 ways in which scientists can share their results

Answer 24

scientific/ peer reviewed articles/ journals

scientific conferences

media reports eg TV, radio