T-lymphocytes are produced in bone marrow and mature in the thymus gland. When mature, T-lymphocytes leave the thymus gland to travel throughout the body. They remain inactive inside organs, such as the spleen and lymph nodes, until activated by the presence of antigens. Fig. 5.1 shows what happens to two inactive T-lymphocytes, U1 and V1, in the presence of an antigen from a virus. [Figure 5.1]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2024). The mark or mark type is shown in brackets.

1. [1] U4 - T-helper (lymphocyte / cell) AND V4 - T-killer / T-cytotoxic (lymphocyte / cell); A 'helper and killer' I helping and killing
2. any four from:
3. U4/helper
4. [1] secretes / produces / releases, cytokines / interleukins; I cell signalling molecules / cytokinins
5. [1] to stimulate, B-lymphocytes / B cells, to, divide / develop into plasma cells ; A stimulates humoral response / clonal expansion / development of memory cells
6. [1] stimulate macrophages to, be active / carry out phagocytosis / respond (to presence of pathogens)/ be ‘angry' ; I endocytosis
7. V4/killer
8. [1] produces / secretes / releases, chemicals, to kill / break down, infected cells ; A (auto)lysis / apoptosis
9. [1] e.g. perforin / hydrogen peroxide / granzymes / proteases ; A hydrolytic enzymes / toxins
10. [1] detail of action of named chemical (see below);
11. [1] AVP; e.g. correct ref to CD4 receptors (on U4 / T-helper) / CD8 receptors on (V4 / T-killer) perforin - makes pores in cell surface membrane of infected cell for delivery of granzymes hydrogen peroxide – oxidises cell components / stimulates apoptosis granzymes / proteases – break down proteins (granzymes are serine proteases)
12. any four from:
13. [1] make vaccine free; I cheap
14. [1] make vaccine available, globally / to whole population (urban and rural) ; I vaccinating people
15. [1] ref to herd immunity / described; e.g. vaccinate a high proportion of the population
16. [1] vaccinate children as early as possible ;
17. [1] ref to provide boosters / use effective vaccine so boosters are not necessary; e.g. live / attenuated, virus
18. [1] accurate record keeping of those vaccinated / find those who have not been vaccinated;
19. [1] surveillance / ref to contact tracing / described; e.g. look out for any cases of the disease
20. [1] start vaccination immediately cases are found / ref to ring immunity / benefits of ring immunity;
21. [1] education about, effects of the disease / benefits of having the vaccine / transmission of the disease ; A counter, misinformation / antivaxers A importance of vaccination
22. [1] make sure there is a sufficient supply of the vaccine ;
23. [1] provide funding for vaccine, production / distribution / delivery ; A provide, cheap / easy to produce, vaccine
24. [1] provide trained personnel ;
25. [1] AVP; e.g. quarantining people with the disease evaluate or monitor success of vaccination programme maintain cold chain (to ensure vaccine is effective) use a thermostable vaccine provide different types of the vaccine (e.g. Sabin (oral) and Salk (injected); different manufacturers for Covid) I develop new vaccines in response to new, strains / variants / AW, of pathogen