A-LevelBiologyImmunity9700/23 · Oct/Nov 2022 · Q214 Marks

Fig. 2.1 is a scanning electron micrograph showing a macrophage engulfing some bacteria. [Figure 2.1]

(a)(i)Describe how macrophages engulf bacteria.[3]
(a)(ii)Explain the functions of lysosomes in cells such as macrophages.[3]
(b)(i)Calculate the percentage change in the number of new cases of TB in the USA between 1993 and 2018. Show all your working. answer .......................................................... %[3]
(b)(ii)Use Fig. 2.2 to describe the trend in the number of new cases of TB in the USA between 1993 and 2018.[2]
(c)Suggest an advantage of calculating the number of new cases per 100000 each year in the prevention and control of TB across the world.[1]
(d)TB is endemic (always present) in many populations across the world and many countries have high numbers of cases. State two reasons why it is difficult to reduce the number of cases of TB across the world.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

[1] phagocytosis / endocytosis ;
[1] (antigens on) bacteria, attach / bind, to cell (surface) membrane / receptors ;
[1] infolding / invagination / pinching in of membrane / AW ;
[1] fusion of membrane of macrophage (to form vacuole) ;
[1] formation of, vacuole / vesicle / phagosome ;
[1] active process / uses ATP / uses energy ;
[1] (lysosomes contain enzymes) to, break down / digest / AW, pathogens / bacteria / viruses ;
[1] (lysosomes contain enzymes) to break down, worn out / old / non-functioning, organelles / cell components ;
[1] using, hydrolytic enzymes / hydrolases ;
[1] isolate harmful enzymes from rest of the cell / membrane-bound to protect rest of cell (from hydrolytic enzymes) ;
[1] AVP ;
[1] (number of new cases in 1993) 25000 – 25 100 ;
[1] (number of new cases in 2018) 8000 – 10000 ;
[1] percentage change = 16 000 / 25 000 x 100 ; answer = – 64(%) / decrease by 64(%) ;
[1] (number of new cases overall) decrease ;
[1] steep(er) decrease between 1993 and 2001 ;
[1] (number of new cases) constant / stable / plateau, between, 2013/2014, to 2018 ;
[1] (number of new cases) increases in 2015 ;
[1] can make, statistical / valid, comparisons between, years / countries ;
[1] Mycobacterium / pathogen / TB bacteria, remains dormant in the body ;
[1] treatment takes a, long time / minimum of 6 months ;
[1] many people do not complete treatment ;
[1] many people do not have access to treatment ;
[1] drug-resistant / antibiotic resistant, strains of Mycobacterium / pathogen / TB bacteria ;
[1] HIV/AIDS or any other medical condition that increases susceptibility to TB ;
[1] vaccine reluctance ;
[1] movement / migration, of people, infected with TB / from countries with high rates of TB ;
[1] poor housing / overcrowded living conditions / homelessness ;
[1] malnutrition / poor diet ;
[1] transmission from cattle by, drinking unpasteurised contaminated milk / eating meat from contaminated cattle ;
[1] lack of education / AW, about preventing spread of TB ;
[1] AVP ;