Topic 6 Immunity, infection and forensics

Question 1

Explain the role of DNA primers in the production of the amplified 345bp sequence. (2)

Answer 1

-Primers have a specific base sequence.
-Bind to complementary bases at either end of DNA be amplified.
-Therefore provide a site for DNA polymerase to bind

Question 2

Devise an investigation to determine the optimum number of cycles for the polymerase chain reaction used to amplify the DNA. (4)

Answer 2

-Use DNA polymerase, primers, and mononucleotides to amplify DNA.
-Ensure temperatures used are kept at 95, 55, 70.
-Change number of cycles.
-Use gel electrophoresis to determine quantity of DNA produced.
-Choose smallest number of cycles that produce an observable band.

Question 3

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. (3)

Answer 3

-Use pigs of the same age/size/sex/mass.
-Control temperature experiment is held at for all bodies.
-Record presence of different species of insects.
-At regular time intervals.

Question 4

Describe how DNA profiling could be carried out to show that two types of snakes are different species. (4)

Answer 4

-DNA obtained from two types of grass snakes.
-PCR/restriction enzymes used to produce fragments of DNA.
-Gel electrophoresis used to analyse DNA samples.
-Gel electrophoresis used to separate fragments of DNA.
-More differences in pattern of bands produced would indicate snakes are different species.

Question 5

Describe the changes that occur inside a body in the first week after death. (3)

Answer 5

-Body temperature falls.
-Rigor mortis/muscles stiffen.
-Autolysis/break down of cells by enzymes in body.
-Discoulouration/bloating.

Question 6

Describe the role of decomposers, such as microorganisms, in the carbon cycle. (2)

Answer 6

-Decomposers break down organic material from dead body.
-Decomposers respire.
-Releasing Carbon dioxide into atmosphere.

Question 7

Explain the effect of temperature on the rate of growth of blowfly maggots. (3)

Answer 7

-Temperature affects enzymes/metabolism.
-An increase in temperature increases kinetic energy.
-Producing more frequent successful collisions between enzyme and substrate molecules.

Question 8

Devise a procedure, using electrophoresis, to compare the amplified DNA from a Neanderthal compared to a modern human. (4)

Answer 8

-Restriction enzymes/endonucleases cut DNA from modern humans and Neanderthals into fragments.
-DNA samples loaded onto agarose gel.
-Electric current passes through gel.
-Fluorescent tags added to visualise bands.
-Position of bands produced can be compared.

Question 9

Explain the effect of ambient temperature on the rate of decomposition. (3)

Answer 9

-An increase in temperature increases rate of decomposition.
-An increase in temperature increases enzyme activity.
-An increase in temperature increases rate of growth of fungi/bacteria/decomposers.

Question 10

Describe how one PCR cycle would increase the quantity of DNA present originally. (3)

Answer 10

-Heat to 95 to break hydrogen bonds between the DNA strands.
-Joining of primers/annealing at 55.
-DNA polymerase involved in forming phosphodiester bonds.
-To double quantity of DNA.

Question 11

Hospitals have developed practices in response to the increase in hospital acquired infections.

Describe the infection control practices hospitals have introduced. (3)

Answer 11

-Hand wash stations.
-Doctors/nurses not allowed to wear ties/watches.
-Testing patients for presence of antibiotic resistant bacteria before admission/isolation of infected patients.
-Increased washing of bedding/disinfection of beds and surfaces.

Question 12

Explain how changes in the blood vessels result in the redness and swelling seen at the site of inflammation. (4)

Answer 12

-Histamine is released.
-Histamine causes arterioles to vasodilate.
-Increasing blood flow to site causing redness.
-Histamine also causes permeability of capillaries to increase.
-Allowing blood plasma to leave capillary causing swelling.

Question 13

Describe how HIV particles are able to enter T helper cells. (3)

Answer 13

-Glycoproteins on surface of virus.
-Bind to CD4 receptors on T helper cells.
-Viral envelope fuses with cell membrane of T helper cell.
-Viral RNA enters cell.

Question 14

Explain why the destruction of T helper cells causes the symptoms of AIDS. (4)

Answer 14

-Lack of T helper cells reduce cytokine production.
-Therefore reduce activation of B cells.
-Reducing antibody production.
-There is an increased risk of opportunistic infections.

Question 15

How does a bacteriostatic antibiotic work? (1)

Answer 15

-It prevents the multiplication of bacteria.

Question 16

What cell produces antibodies? (1)

Answer 16

-Plasma cell.

Question 17

What is the type of immunity that a newborn baby obtains from milk produced by its mother? (1)

Answer 17

-Natural passive immunity.

Question 18

Explain why the presence of microorganisms on the skin and in the gut helps to prevent pathogenic organisms multiplying in the body. (3)

Answer 18

-Flora in gut and skin are better adapted to the conditions.
-Therefore they can outcompete pathogenic organisms.
-Bacteria in gut secrete chemicals/lactic acid which helps to destroy pathogens.

Question 19

Devise a laboratory procedure to compare the effectiveness of penicillin with new antibiotics. (6)

Answer 19

-Prepare agar plates with bacterial cultures, use bacteria that are resistant to other antibiotics.
-Prepare solutions of new antibiotic and penicillin.
-Place onto paper discs.
-Control time and temperature of incubation.
-Same concertation and volume of both antibiotics.
-Measure area/zone of inhibition.
-Repeat for effective antibiotics.
-Repeat with different strains of resistant bacteria.

Question 20

Human papilloma virus (HPV) is a DNA virus.
Cervarix and Guardasil have been used in national vaccination programs.

A person who has been vaccinated becomes infected with HPV-16. Explain the role of the T cells in the body of this person. (3)

Answer 20

-A vaccinated person will have memory T cells.
-Memory T cells recognise antigens specific to HPV-16 virus.
-T helper cells that activate B cells/T killer cells.
-Formation of T killer cells destroy cells infected with virus.

Question 21

The human gut contains more than a thousand species of bacteria. Only 30 to 40 of these species are found in the stomach.

Explain why there are relatively few species of bacteria in the stomach. (2)

Answer 21

-As the pH inside stomach is too low for enzymes of most bacteria to function.
-Bacteria that live in stomach have adaptations that enable them to survive.

Question 22

Explain the role of T cells in the immunity to the Ebola virus that develops following the use of this vaccine. (3)

Answer 22

-T helper cells bind to protein/antigen on antigen presenting cell.
-Therefore leading to production of active T helper cells/memory T cells.
-T helper cells activate B cells to divide/become cells capable of producing antibodies.
-Memory cells remain in body so antibodies can be produced quickly on re-infection.