OCR, June 2000

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

        Question:

      1. Similarity

        Answer:

        similarity rise in number of cases of AIDS;

        S-shaped curve;

        both peak in 1990;


        Question:

      2. Difference

        Answer:

        difference earlier rise for homosexuals/bisexuals;

        earlier levelling off in number of new cases for homo/bisexuals;

        fewer cases in drug users;


      [2]
      Question:

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

      [1]
      Answer:

      (earlier rise for homosexuals/bisexuals) because gay community first infected;

      (earlier levelling off in new cases for homo/bisexuals) because more aware of need for/more able to take preventative measures;


      Question:

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

      [3]
      Answer:

      use of clean, needles/syringes/reduced sharing of contaminated, needles/syringes;

      provided free (by, local authorities/Government);

      availability of more effective drug treatments;

      education/advertising campaigns;

      Not "safe sex".


    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

      Answer:

      component surface glycoprotein;


      Question:

    2. reason

      Answer:

      reason glycoproteins often, antigenic/epitopic;

      stimulate response from immune system;

      proteins exposed on surface of, virus/infected cell, easy to attack for antibodies;


    [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]
    Answer:

    prevents conversion of RNA of virus into DNA in host;

    DNA enters host cell nucleus and integrates with host DNA;

    this necessary before virus can replicate;


    Question:

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

    [2]
    Answer:

    antibiotics interfere with metabolic processes;

    e.g. metabolic process; (e.g. cell wall synthesis/protein synthesis/cell membrane function/enzyme action)

    viruses do not have, metabolism/relevant metabolic process;


    Question:

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

    [3]
    Answer:

    HIV destroys. T helper cells/lymphocytes;

    T helper cells needed for correct functioning of, immune system/T & B cells;

    T cells eliminate viral infection/B cells make antibodies;

    opportunistic infections therefore occur/no resistance to common patnogens;

    cancers not recognised and eliminated;

    example; (e.g. TB, fungal pathogens such as candidiasis/oral thrush, secondary cancers, Kaposi's sarcoma, skin cancer, herpes, Pneumocytis/rare form of, pneumonia, food poisoning, toxoplasmosis, brain lesions, cryptosporidiosis, diarrhoea.)


[Total : 15]