immune response

Question 1

Suggest why it is advisable for people to be vaccinated against influenza every year.

______________________________________________________________

Answer 1

Different strain / type of virus each year / virus mutates;
With different antigens;
Influenza antibodies / memory cells (rapidly) destroyed / need replacing

Question 2

Azidothymidine (AZT) is a drug used to treat people infected with human

immunodeficiency virus (HIV). It inhibits the enzyme that synthesises

DNA from HIV RNA. This does not destroy HIV in the body but stops or

slows the development of AIDS.

5 In the past, some people who took AZT on its own eventually developed

AIDS. Some of the HIV in their bodies had become resistant to AZT.

To prevent this from happening, people infected with HIV are now treated

with highly active antiretroviral therapy (HAART). This involves taking AZT

with other anti-HIV drugs at the same time.

10 AZT is taken in low doses. This is because people who took high doses

over long periods of time suffered muscle wastage. It was found that high

doses of AZT inhibit replication of mitochondria.

Use information from the passage and your own knowledge to answer the questions.

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

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

(4)

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

Advantage 1 ________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

Advantage 2 ___________________________________

Answer 2

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);
7. Context is important
8. Allow slows / stops (re)production of HIV
9. Reject (AZT) prevents DNA replication

4 max

(b) 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;
4. Because HAART prevents the spread of AZT-resistant HIV to rest of the human population;

OR

5. No new HIV particles made;
6. Because HAART might interfere with viral protein synthesis;

Question 4

(ii) The information in the pie chart is valuable to companies who make influenza vaccines. Use your knowledge of antigens to explain why.

Answer 4

Vaccines only work against certain strains because the antigens they possess are different;

Enables company to target strain likely to be prevalent later / most common strain;

2

[

Question 5

An influenza virus consists of a protein coat surrounding nucleic acid. The influenza vaccine consists only of the protein coat of the virus. Explain how the influenza vaccine produces immunity in the body.

Answer 5

(Protein coat) carries antigens which stimulates B-cells / production of antibodies;
Production of memory cells;

Question 6

Explain how a blood transfusion from a patient recently recovered from Ebola may be an effective treatment (lines 8–10)

Answer 6

Lots of antibodies (against Ebola) in recovered patient;

2. Transfusion/plasma contains antibodies;

Ignore reference to cells

3. Antibodies (specific so) will bind with (Ebola) antigen;
4. (In recipient) virus destroyed/cannot enter cell;

Question 7

A high mutation rate makes it difficult to develop a vaccine (line 11).

Explain why.

_____________________

Answer 7

(High mutation rate leads to) antigens change/antigenic variability;

Accept (high mutation rate leads to) changes in base sequence coding for antigen;

2. Vaccine contains specific antigen;
3. Antibodies not complementary to (changed) antigen / won’t bind to (changed) antigens;

Question 8

Suggest two reasons why the percentage of infants vaccinated decreased between 1973 and 1975.

Answer 8

Any two from:

1. (Decrease linked to) few(er) cases of whooping cough;
2. (Decrease linked to) risk of / fear of side effects;
3. Insufficient vaccine available / too expensive to produce / distribute.

Question 9

The percentage of the population vaccinated does not need to be 100% to be effective in preventing the spread of whooping cough.

Suggest why.

Answer 9

More people are immune / fewer people carry the pathogen;

So susceptible / unvaccinated people less likely to contact infected people.

Question 10

Give two factors, other than cost, that should be considered when selecting an antibiotic to treat a bacterial disease.

Answer 10

side effects / allergic reactions / low toxicity to cells;
interaction with other drugs / effective in conditions of use / reasonably stable;
should only act on the problem bacteria / narrow spectrum;
how much resistance the bacteria have built up;