It is estimated that more people died of the bacterial disease tuberculosis (TB) in 1999 than in any other year in history. Scientists are fighting the battle against the disease on several fronts. For example, the complete DNA sequence of 4 million base pairs of the causative agent has recently been determined. Epidemiological research is also important. In the suburbs of Cape Town, South Africa, for example, the disease is, as expected, most common in the poorer suburbs. But there is also a marked correlation between the incidence of TB and infections by intestinal parasites. This may be because such parasites stimulate T-lymphocytes to activate B-lymphocytes and suppress the activity of macrophages.

Question:


1. Name the most common causative agent of TB.

   [1]
   

   Answer:

   Mycobacterium tuberculosis;

   
   Question:
   

2. Explain what is meant by epidemiological research.

   [2]
   

   Answer:

   epidemiology is the study of pattern of disease;factors that affect the spread of disease;how diseases affect whole populations (not just individuals);search for common factors amongst people who develop a disease;

   
   Question:
   

3. State two reasons why TB was expected to be most common in the poorer suburbs of Cape Town.

   [2]
   

   Answer:

   associated with overcrowding;because spread by droplet infection/coughing/sneezing;associated with poor housing;low immunity due to poor diet;link with HIV which is more common in poor areas;A.V.P.;

   
   Question:
   

4. Suggest one reason why knowledge of the DNA base sequence of the causative organism could help in the fight against the disease.

   [1]
   

   Answer:

   identify parts of the organism that can be targeted with new drugs/vaccines;help to develop vaccines by genetic engineering;help to select genes to code for proteins that may be useful as vaccines;easier identification of different strains of the disease;follow evolution/development of new strains;

   
   Question:
   

5. Summarise the main reasons why TB is still such a widespread disease.

   [4]
   

   Answer:

   some strains of TB are resistant to drugs/antibiotics;AIDS damages immune system and TB common secondary infection;large reservoir of disease/many people are carriers/have dormant TB bacteria;rising homelessness/poverty in inner cities of developed world;drug treatment programmes often not completed increasing risk of drug resistance;vaccine not very effective/reliable;can spread from animals/cattle;

   
   Question:
   

6. Describe briefly the differences in the way the B- and T-lymphocytes act during the immune response.

   [3]
   

   Answer:

   T cells attack virus-infected cells;and transplanted organs (tissues)/cancer causing cells;whose cell involved in attack/cell mediated immunity;B cells release antibody/humoral immunity;attack bacteria (and some viruses);

   
   Question:
   

7. Explain why suppression of macrophages lowers resistance to TB.

   [2]
   

   Answer:

   macrophages engulf and destroy bacteria;(circulate in blood and) pass into organs such as lungs;where TB bacteria tend to accumulate/infect;TB bacteria found inside cells where difficult for antibodies to attack them;