A class of students was studying the features of some human pathogens. One of the students constructed a flow chart to identify four different human pathogens. The student used information about the structure and mode of transmission of each of these pathogens. Fig. 3.1 shows the partially completed flow chart. [Figure 3.1] Complete the flow chart in Fig. 3.1 by identifying: • the modes of transmission • the scientific names of the pathogens • the name of one of the diseases.

Mark scheme

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

1. [5] (malaria) pathogen is transmitted by: (insect) vector / Anopheles / (a) mosquito;
2. [5] (malaria) pathogen: Plasmodium, falciparum / ovale / malariae / vivax ; A knowlesi
3. [5] (tuberculosis) pathogen is transmitted by: airborne droplets / droplet infection / aerosol (infection); I air droplets I water droplets from, coughing / sneezing A alternative transmission only if Mycobacterium bovis stated e.g. (eating) contaminated meat (from infected cattle) (drinking) contaminated milk (drinking) unpasteurised milk from contaminated, cows / cattle
4. [5] (tuberculosis) pathogen: Mycobacterium, tuberculosis / bovis ;
5. [5] (faecal-oral route disease): Vibrio cholerae and cholera ; A other pathogens and associated diseases that are transmitted in the same way
6. [2] any two from:
7. [2] tenofovir competes with, (activated / phosphorylated) adenine nucleotide / deoxyribose adenosine triphosphate / dATP, for active site / to prevent nucleotides being added to elongating chain ; A (tenofovir acts as a) competitive inhibitor (of reverse transcriptase)
8. [2] tenofovir forms a phosphodiester bond to elongating DNA strand, but stops further reactions / AW;
9. [2] tenofovir has, no 3´ -OH so next nucleotide cannot form a phosphodiester bond / no (deoxyribose so cannot form phosphodiester bond ; A pentose R sugar unqualified
10. [1] 20 (%); R answers with decimal places
11. [4] there must be at least one statement or at least one explanation to gain max 4, otherwise mark to max 3
12. [4] any four from:
13. [4] 1 supply, condoms / femidoms / dental dams / item(s) for protection during sex ;
14. [4] 2 barrier to transmission during sexual intercourse ;
15. [4] 3 ref. to, needle exchange schemes / other suitable support for intravenous drug (ab)users ; I clean needles
16. [4] 4 decreases risk of sharing contaminated equipment / AW ;
17. [4] 5 use, new needles / new syringes / sterilised equipment / AW, for medical procedures ; I clean needles
18. [4] 6 decreases risk of transmission from contaminated blood;
19. [4] 7 provide testing for HIV, in high risk groups / to individuals at high risk ;
20. [4] 8 for early diagnosis so newly infected people so can start drug treatment immediately;
21. [4] 8 test pregnant women for HIV / provide powdered milk to women who are HIV positive;
22. [4] 9 prevent women who are HIV positive passing HIV in breast milk ;
23. [4] 10 prevent people who are HIV positive being blood donors / screen donated blood / heat-treat donated blood;
24. [4] 11 prevent receiving blood infected with HIV, during blood transfusions / operations ;
25. [4] 12 carry out contact tracing;
26. [4] 13 locate people who, are undiagnosed / may be HIV positive / should be offered test ;
27. [4] 14 supply (named) drug(s) to people, living with HIV / who are HIV positive / pregnant women with HIV ;
28. [4] 15 prevents HIV, spreading throughout the body / infecting more T-lymphocytes ; A to reduce viral load
29. [4] 16 provide, education / information, about, HIV treatments / HIV transmission ;
30. [4] 17 to raise awareness of ways to reduce infection / AW; A use of barrier methods during sex / safer sex
31. [4] 18 AVP; e.g. law to make it illegal to knowingly transmit the virus