p2

Question 1

Using the graph above, what can you conclude about the effectiveness of
each injection on the immune response of these mice?
4 marker

Answer 1

(1)- 1st injection protects some mice
(1)- 2nd and 3rd infection causes a secondary response and memory cells so protects all mice
(1)- this is because antibody is above protective level
(1)- no mice protected after 180 days, injections is not effective long term

Question 2

The scientists hypothesised that memory B cells had formed in the mice
180 days after the 3rd injection.
Suggest and explain a practical method the scientists could use to test this
hypothesis.
2 marker

Answer 2

(1)- inject vaccine again
(1)- immune response will be quicker than 1st infection
(1)- add enzyme attached to second antibody against memory cells
(1)- add substrate and colour change means memory cells are present

Question 3

When a person is bitten by a venomous snake, the snake injects a toxin
into the person. Antivenom is injected as treatment. Antivenom contains
antibodies against the snake toxin. This treatment is an example of passive
immunity.
Explain how the treatment with antivenom works and why it is essential to
use passive immunity, rather than active immunity.
2 marker

Answer 3

(1)- antibodies bind to the venom and cause its destruction
(1)- active immunity would be too slow

Question 4

A mixture of venoms from several snakes of the same species is used.
Suggest why.
2 marker

Answer 4

(1)- snakes within the 1 species may have different mutation
(1)-several antibodies are complementary to several antigens

Question 5

During vaccination, each animal is initially injected with a small volume of
venom. Two weeks later, it is injected with a larger volume of venom.
Use your knowledge of the humoral immune response to explain this
vaccination programme.
3 marker

Answer 5

(1)- b cells are specific to the venom clone
(1)- b cells produce plasma cells and memory cells
(1)-the second dose produces antibodies in higher concentration and quickly

Question 6

Suggest and explain why AZT does not destroy HIV in the body but stops
or slows the development of AIDS (lines 3–4).
4 marker

Answer 6

1. Person (infected with HIV) has HIV DNA (in their DNA);
2. New HIV (particles) still made;
3. (AZT) inhibits reverse transcriptase;
4. (AZT) stops these (new HIV particles) from forming new HIV DNA;
5. Stops destruction of more / newly infected T cells;
6. So immune system continues to work (and AIDS does not

Question 7

Suggest and explain two advantages of using HAART (lines 7–9).
4 marker

Answer 7

1. Slows / stops the development of AIDS;
2. Because HIV resistant to AZT is damaged / destroyed /
   prevented from replicating (by other drugs);
   OR
   3.AZT continues to work as a drug;
3. Because HAART prevents the spread of AZT-resistant HIV to rest of the human population;
   OR
4. No new HIV particles made;
5. Because HAART might interfere with viral protein synthesis;

Question 8

Describe how phagocytosis of a virus leads to presentation of its antigens.
3 marker

Answer 8

(1)-phagososme fuses with lysosome
(1)-virus is destroyed by lysozymes
(1)-antigens from virus are displayed on cell membrane

Question 9

Describe how presentation of a virus antigen leads to the secretion of an
antibody against this virus antigen.
3 marker

Answer 9

(1)-helper T cells bind to antigen
(1)- this helper T cell stimulate b cells to undergo clonal expansion
(1)-froms plasma cells which release antibodies quickly

Question 10

Explain the differences between the mean concentrations of antibodies in
blood samples 1, 2 and 3.
4 marker

Answer 10

1. Sample 1 / before vaccination no antibody released because patients not yet encountered vaccine / antigen / virus;
2. (Sample 2 / primary response / after first dose) activation / clonal
   selection / expansion of B cells into plasma cells;
3. Plasma cells release antibodies;
4. (Sample 3 / secondary response / after second dose) memory cells
   produce more antibodies / produce antibodies more quickly;

Question 11

Bacterial meningitis is a potentially fatal disease affecting the membranes around
the brain. Neisseria meningitidis (Nm) is a leading cause of bacterial meningitis.
(a) In the UK, children are vaccinated against this disease. Describe how
vaccination can lead to protection against bacterial meningitis.
6 marker

Answer 11

1. Antigen binds to surface receptor on a (specific / single) B cell.
2. (Activated) B cell divides by mitosis / produces clone;
   3.(Division) stimulated by cytokines / by T cells;
   4.B cells / plasma cells release antibodies;
3. (Some) B cells become memory cells;
4. Memory cells produce plasma / antibodies faster