Fig. 1 shows the number of cases of AIDS between the years 1981 to 1991 for two groups of people in Europe; those who are homosexual or bisexual and those who are injecting drug users.

1. 1. State one similarity and one difference between the data for the two groups of people between 1981 and 1990.

      Question:
      

      1. Similarity

         Question:
         

      2. Difference

      [2]
      Question:
      

   2. Suggest one reason for the difference you have identified in (a)(i).

      [1]
      Question:
      

   3. Explain briefly, the decline in the number of cases of AIDS among injecting drug users between 1990 and 1991.

      [3]
      

   Fig. 2 is a diagram of the structure of the human immunodeficiency virus (HIV), the causative agent of AIDS.

2. Predict one component of the virus, shown in Fig. 2, which would be likely to be of importance in producing a vaccine against the virus. Give a reason for your answer.

   Question:
   

   1. component

      Question:
      

   2. reason

   [2]
   Question:
   

3. The drug zidovudine (AZT) is an inhibitor of the enzyme reverse transcriptase. Explain why AZT slows down the progress of HIV infection.

   [2]
   Question:
   

4. Explain why antibiotics are ineffective against HIV and other viruses.

   [2]
   Question:
   

5. Explain the link between the infection of T-lymphocytes by HIV and the onset of the symptoms of AIDS.

   [3]