Immunology

Question 1

Use the data in the table above and your knowledge of the immune response to suggesr why HIV controllers do not develop symptoms of AIDS

Answer 1

• HIV controllers have more CD4 cells
• And a lower viral load to infect T cells
• So there is more activation of B cells, cytotoxic T cells and phagocytes
• With more B cells, more plasma and more antibodies being produced
• Body is able to destroy other microbes/pathogens someone who suffers from AIDS wouldn’t be able to

Question 2

Describe how HIV is replicated

Answer 2

• Attachment proteins on HIV attach to receptors on T cell.
• RNA enters T cell
• Reverse transcriptase changes viral RNA to viral DNA
• Viral protein, capsid and enzymes produced
• Virus assembled and released from cell.

Question 3

Describe how the human immunodeficiency virus is replicated once inside helper t cells

Answer 3

• RNA converted into DNA using reverse transcriptase
• DNA incorporated into helper t cell DNA
• DNA transcribed into HIV mRNA
• 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

Engulfs
Forming phagosome and fuses with lysosome
Lysozymes hydrolyze

Question 5

Determining the genome of the viruses could allow scientists to develop a vaccine
Explain how

Answer 5

Scientists could identify proteins
They could then identify potential antigens

Question 6

What is a monoclonal antibody

Answer 6

Antibodies with the same tertiary structure

OR

An antibody produced from identical/ cloned plasma cell/ B cells

Question 7

Describe and explain the role of antibodies in stimulating phagocytosis

Answer 7

Antibodies bind to antigens and are markers
They cause clumping and agglutination which attracts phagocytes

Question 8

During vaccination, each animal is initially injected with a small volume of Venom. 2 weeks later it is injected with a larger volume of Venom.

Use your knowledge of the humoral immune response to explain this vaccination program

Answer 8

• B Cell specific to the Venom reproduced by mitosis
• B Cells produce plasma cells and memory cells
• The second dose produces antibodies in secondary immune response in higher concentrations and more quickly

Question 9

In the UK, children are vaccinated against NM. Describe how vaccination can lead to protection against NM

Answer 9

• Antigen on surface of NM binds the surface protein on a B cell
• B. Cell divides by mitosis
• Stimulated by t cells
• B. Cells/ plasma cells release antibodies
• B cells become memory cells
• Memory cells produce plasma/ antibodies faster

Question 10

When a vaccine is given to a person, it leads to the production of antibodies against a disease causing organism. Describe how

Answer 10

• Vaccine contains antigen from pathogen
• Body cell presents antigen on its surface
• T cell with complementary receptor protein binds to antigen
• T. Cell stimulates B. Cell
• With complementary antibody on its surface
• B. Cell secretes large amounts of antibody
• B. Cell device to form clone or secreting/producing the same antibody

Question 11

Explain why the number of hiv particles in the blood rises during the first few months after infection

Answer 11

• hiv is invading cells which make new viruses
  2. Cells release viruses into blood a

Question 12

Describe how antibodies are produced in the body following a viral infection

Answer 12

1. virus contains antigen;
2. virus engulfed by phagocyte
3. presents antigen to B-cell
4. memory cells / B-cell becomes activated;
5. (divides to) form clones
6. by mitosis;
7. plasma cells produce antibodies;
8. antibodies specific to antigen;
9. correct reference to T-cells / cytokines

Question 13

AZT inhibits the enzyme that synthesises DNA from HIV RNA. explain why it does not destroy HIV in the body but stops or slows the development of AIDS

Answer 13

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;
   OR
   Slows / stops replication of HIV;
5. Stops destruction of more / newly infected
   T cells;
6. So immune system continues to work (and
   AIDS does not develop);

Question 14

Explain why viruses are described as acellular and non living

Answer 14

Acellular - no cell surface membrane
Non living- cannot reproduce on its own

Question 15

Give one reason why antibiotics are not effective against viruses

Answer 15

Do not have bacterial structures/enzymes
OR
Do not have metabolic processes
OR
Do not have a cell wall/murein;

Question 16

Explain how the use of antibiotics has led to antibiotic-resistant strains of bacteria becoming a common cause of infection acquired when in hospital

Answer 16

1. (Some bacteria have) alleles
   for resistance;
2. (Exposure to) antibiotics is the
   selection pressure
   OR
   Non-resistant bacteria die
   OR
   Resistant bacteria
   survive/reproduce;
3. More antibiotics used in
   hospital (compared with
   elsewhere)
   OR
   Patients have weakened
   immune systems
   OR
   (So) high frequency of
   resistance allele (in bacterial
   population);

Question 17

Suggest and explain one reason why bacteria resistant to tetracycline are more common than bacteria resistant to streptomycin in these farm animals

(Context is not necessary)

Answer 17

1. Tetracycline used more often / in higher doses;
2. Resistant bacteria more likely to (survive and reproduce and) pass on allele/gene for (tetracycline) resistance;

OR

3. More / higher frequency of mutations (for tetracycline resistance);
4. (so) gene passed on to more bacteria;

OR

5. Tetracycline used over longer time period;
6. More time for (chance) mutation to occur / for selection to occur;

Question 18

During an ELISA test, a control well is always used. This is treated the exact same as the test well, except the blood plasma is replaced by salt solution.
Explain 2 purposes of the control well

Answer 18

1. Only the enzyme/nothing else is causing a
   colour change;
2. Washing is effective/all unbound antibody is washed away;

Question 19

How are viral proteins produced inside an infected helper T cell (4)

Answer 19

• viral RNA uses reverse transcriptase to make cDNA (will not get mark without saying cDNA)
• integrated into t cell DNA with integrase
• viral mRNA transcribed into hiv proteins
• translation takes place at ribosome
• protease is used to modify viral proteins

Question 20

Suggest how AZT could prevent the onset of AIDS (3)

Answer 20

• both have similar structure, so AZT competes with nucleotide containing thymidine
• AZT does not have -OH to join with another nucleotide
• formation of viral DNA strand is stopped
  Or
• prevents transcription of viral DNA
  Or
• viral replication prevented so decreases number of HIT particles in plasma

Question 21

Suggest why cells in tumours can be destroyed by the immune system [3]

Answer 21

1. Faulty protein recognised as an antigen / as a ‘foreign’ protein;
2. T cells will bind to faulty protein / to (this) ‘foreign’ protein;
3. (Sensitised) T cells will stimulate clonal selection of B cells;
4. (Resulting in) release of antibodies against faulty protein