5 The vaccine used to control tuberculosis (TB) is known as Bacillus Calmette-Guérin (BCG). The vaccine contains live bacteria that have been selected so that they do not cause disease in humans. Fig. 5.1 shows a macrophage that is in the process of engulfing the bacteria in the vaccine. magnification x4400 [Figure 5.1]

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

1. [1] Mycobacterium tuberculosis or Mycobacterium bovis ;
2. [2] max1 if no reference to, infected/uninfected
3. airborne droplets, breathed / sneezed / AW, out by infected person ;
4. breathed in / inhaled / inspired, by uninfected person ;
5. or
6. in context of M. bovis only
7. contaminated meat / unpasteurised milk, from infected, cattle / cows ;
8. ingested by uninfected person ;
9. [5] max 4 if no ref. to, (mature) B-lymphocytes / plasma cells, producing / secreting, antibodies
10. any five from: ref. to fusion of lysosomes releasing hydrolytic enzymes ;
11. intracellular digestion / described; e.g. hydrolysis of, (named) cell wall components / proteins / nucleic acids / lipids
12. ref. to processing antigens to present on, cell surface membrane / cell surface ; A macrophage becomes an, antigen presenting cell / APC ;
13. antigen, recognition / binding, by, B-lymphocytes / T-lymphocytes ;
14. detail; e.g. clonal selection / have receptors complementary to antigen / specificity of, B-lymphocytes /T- lymphocytes to (non-self) antigen ; A immunoglobulin / antibody as receptor for B-lymphocytes
15. clonal, expansion / proliferation;
16. A described e.g. divides by mitosis to form a clone of cells
17. B-lymphocytes, mature to / form, plasma cells that secrete antibodies;
18. T-helper cells release cytokines ;
19. Cytokine action; e.g. stimulates, humoral / B-lymphocyte, response
20. [3] any three from: long-term immunity;
21. B and T memory cells remain in the body for, a long time / a lifetime;
22. memory cells for secondary (immune) response ;
23. secondary response is faster / more effective (than primary immune response);
24. (so) higher concentration antibodies / quicker production antibodies ;
25. Idea of more (specific) memory cells in the body than (specific) lymphocytes before primary response ;
26. increase chance that pathogen encountered more rapidly (to mount a response) ;
27. AVP; e.g. pathogen destroyed before symptoms of illness are caused
28. [3] any three from: Mycobacterium / TB bacterium, is an intracellular parasite / lives inside host cells ;
29. antibodies have no effect on bacteria inside cells;
30. only when bacteria are in the, plasma / tissue fluid ;
31. idea that vaccination is not a global occurrence ; e.g. not part of vaccination programme in many countries only some countries have as part of their vaccination programme
32. BCG is not very effective (for adults) / some people do not respond to BCG ;
33. BCG does not have the same effectiveness across the world;
34. many countries, have no herd immunity / do have enough people that are immune, to prevent spread;
35. ref. to civil disturbance / AW, collapse of health services ;
36. AVP; idea that travellers / tourists / immigrants / displaced people, may be infected with TB and transmit it to host population (that does not have, a vaccination programme / herd immunity)