biology immune response past paper questions

Question 1

Describe how HIV is replicated.
5 marks

Answer 1

1. Attachment proteins attach to receptors on helper T cell/lymphocyte;
2. Nucleic acid/RNA enters cell;
3. Reverse transcriptase converts RNA to DNA;
4. Viral protein/capsid/enzymes produced;
5. 5. Virus (particles) assembled and released (from cell).

Question 2

Describe how an ADC enters and kills the tumour cell.

Answer 2

1. Cell ingests/engulfs the antibody/ADC OR Cell membrane surrounds the antibody/ADC (to take it inside the cell);
2. Lysosomes fuse with vesicle/phagosome (containing ADC);
3. Lysozymes breakdown/digest the antibody/ADC to release the drug.

Question 3

Describe how HIV is replicated once inside helper T cells.

Answer 3

1. RNA converted into DNA using reverse transcriptase;
2. DNA incorporated/inserted into (helper T cell) DNA/chromosome/genome/nucleus;
3. DNA transcribed into (HIV m)RNA;
4. (HIV mRNA) translated into (new) HIV/viral proteins (for assembly into viral particles).

Question 4

Describe how a phagocyte destroys a pathogen present in the blood.

Answer 4

1. Engulfs;
2. Forming vesicle/phagosome and fuses with lysosome;
3. Enzymes digest/hydrolyse.

Question 5

Give two types of cell, other than pathogens, that can stimulate an immune response.

Answer 5

1. Tumour cells;
2. Cells from transplants.

Question 6

Explain how HIV affects the production of antibodies when AIDS develops in a person.

Answer 6

1. Less/no antibody produced;
2. (Because HIV) destroys helper T cells;
3. (So) few/no B cells activated/stimulated OR (So) few/no B cells undergo mitosis/differentiate/form plasma cells.

Question 7

Suggest and explain how the viruses became able to infect other species of frog.

Answer 7

1. Mutation in the viral DNA/RNA/genome/genetic material;
2. Altered (tertiary structure of the) viral attachment protein;
3. Allows it/attachment protein/virus to bind (to receptors of other species).

Question 8

Describe how the B lymphocytes of a frog would respond to vaccination against Ranavirus.

Answer 8

1. B cell (antibody) binds to (viral) specific/complementary receptor/antigen; 2. B cell clones OR B cell divides by mitosis; 3. Plasma cells release/produce (monoclonal) antibodies (against the virus); 4. (B/plasma cells produce/develop) memory cells.

Question 9

What is a monoclonal antibody?

Answer 9

Antibodies with the same tertiary structure OR (Antibody produced from) identical/cloned plasma cells/B cells/B lymphocytes.

Question 10

Describe the role of antibodies in producing a positive result in an ELISA test.

Answer 10

1. (First) antibody binds/attaches/complementary (in shape) to antigen;
2. (Second) antibody with enzyme attached is added;
3. (Second) antibody attaches to antigen;
4. (Substrate/solution added) and colour changes.

Question 11

Explain how the treatment with antivenom works and why it is essential to use passive immunity, rather than active immunity.

Answer 11

1. (Antivenom/Passive immunity) antibodies bind to the toxin/venom/antigen and (causes) its destruction;
2. Active immunity would be too slow/slower.

Question 12

Why is a mixture of venoms from several snakes of the same species used?

Answer 12

1. May be different forms of antigen/toxin (within one species) OR Snakes (within one species) may have different mutations/alleles;
2. Different antibodies (needed in the antivenom) OR (Several) antibodies complementary (to several antigens).

Question 13

Use your knowledge of the humoral immune response to explain the vaccination programme involving venom.

Answer 13

1. Each animal is initially injected with a small volume of venom;
2. Two weeks later, it is injected with a larger volume of venom.

Question 14

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

Answer 14

1. Phagosome/vesicle fuses with lysosome; 2. (Virus) destroyed by lysozymes/hydrolytic enzymes;
2. Peptides/antigen (from virus) are displayed on the cell membrane.

Question 15

Describe how vaccination can lead to protection against bacterial meningitis.

Answer 15

1. Antigen/epitope on surface of N. meningitidis/bacterium binds to surface protein/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; 5. (Some) B cells become memory cells;
5. Memory cells produce plasma/antibodies faster.

Question 16

Describe the difference between active and passive immunity.

Answer 16

1. Active involves memory cells, passive does not;
2. Active involves production of antibody by plasma cells/memory cells;
3. Passive involves antibody introduced into body from outside/named source;
4. Active long term, because antibody produced in response to antigen;
5. Passive short term, because antibody (given) is broken down; Active (can) take time to develop/work, passive fast acting.

Question 17

Describe how a vaccine leads to the production of antibodies against a disease-causing organism.

Answer 17

1. Vaccine contains antigen from pathogen; 2. Macrophage presents antigen on its surface;
2. T cell with complementary receptor protein binds to antigen;
3. T cell stimulates B cell;
4. (With) complementary antibody on its surface;
5. B cell secretes large amounts of antibody;
6. B cell divides to form clone all secreting/producing same antibody.