Vaccination, HIV and antibioticsAQA A-Level Biology: Subtopic test

1. 1
   A town has a population of 40 000. Health officials have vaccinated 95% of the population against measles. Measles spreads easily from person to person by droplets. Babies under one year, and people whose immune systems are suppressed by drugs, cannot be given the vaccine.

   (a)

   How many people in the town are unvaccinated?

   [1 mark]

   • A200
   • B2000
   • C3800
   • D38 000

   (b)

   Which group in the town benefits most from herd immunity?

   [1 mark]

   • AAdults who have been vaccinated and have memory cells
   • BPeople who have recovered from measles and have memory cells
   • CEveryone equally, because the vaccine gives passive immunity
   • DBabies and people with suppressed immune systems, who cannot be vaccinated

   (c)

   Explain how a high vaccination rate protects the babies in the town from measles.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A traveller is bitten by a dog in a region where rabies is common. At the clinic she is given an injection of human rabies antibodies, and she is also given a course of rabies vaccine.

   (a)

   Which statement correctly describes the injection of human rabies antibodies?

   [1 mark]

   • APassive immunity, giving immediate but short-term protection
   • BActive immunity, giving long-term protection through memory cells
   • CPassive immunity, stimulating the traveller's B cells to divide
   • DActive immunity, giving immediate protection through plasma cells

   (b)

   Why is the rabies vaccine also given?

   [1 mark]

   • AIt gives immediate protection because it contains antibodies
   • BIt is passive immunity that lasts longer than the injected antibodies
   • CIt stimulates her own B cells to produce antibodies and memory cells, giving long-term protection
   • DIt destroys the virus directly

   (c)

   Explain why the injected antibodies protect the traveller for only a short time.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A man diagnosed with HIV infection had a helper T cell count of 800 cells per mm³ of blood. Eight years later, without treatment, the count had fallen to 150 cells per mm³ and he was suffering from recurrent pneumonia and tuberculosis.

   (a)

   Describe how HIV enters and replicates in a helper T cell.

   [3 marks]

   (b)

   Explain why the man now suffers recurrent infections such as pneumonia and tuberculosis.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hospital in a region where tuberculosis (TB) and HIV infection are both common treats a patient who has HIV and has also developed TB, which is caused by a bacterium. The patient is prescribed an antibiotic for the TB. Separately, a trial of a new TB vaccine involved 10 000 volunteers randomly allocated to two equal groups, one given the vaccine and one given a placebo. Over three years, 12 TB cases occurred in the vaccinated group and 30 in the placebo group.

   (a)

   Explain why antibiotics are suitable for treating the patient's TB but are ineffective against HIV.

   [6 marks]

   (b)

   Evaluate the evidence from the trial for using the new TB vaccine, and discuss ethical issues in testing and using it.

   [6 marks]

   Total for question 4: 12 marks

End of questions