A-LevelBiologyCell structure9700/22 · May/June 2024 · Q212 Marks

Alveolar macrophages are cells of the immune system that remain in the alveolar region of the gas exchange system. The macrophages protect against infection caused by pathogens that have been inhaled.

(a)(i)Alveolar macrophages have the same cell structures as typical animal cells. Complete Table 2.1 to name the cell structures that match the functions stated. Do not use abbreviations. [Table 2.1 with functions: manufactures ribosomal subunits from proteins and ribosomal RNA; synthesises triglycerides and other lipids; organise microtubules of the cell cytoskeleton][3]
(a)(ii)[Figure 2.1] is a diagram of an alveolar macrophage showing: • some of the cell structures that would be visible using an electron microscope • a newly formed phagocytic vacuole (phagosome) containing two cells of Mycobacterium tuberculosis. The cell structures with the functions described in Table 2.1 are not shown in Fig. 2.1. Complete Fig. 2.1 by drawing and labelling the cell structures described in Table 2.1.[2]
(b)(i)Tuberculosis (TB) can be prevented if the bacterial cells that have reached the alveoli are rapidly destroyed. Alveolar macrophages can detect the presence of M. tuberculosis in the alveolar space and can carry out phagocytosis to form phagocytic vacuoles, such as the one shown in Fig. 2.1. Outline the sequence of events that leads to the formation of a phagocytic vacuole after detection of the bacterial cells by an alveolar macrophage.[2]
(b)(ii)Name the cell structures that fuse with the phagocytic vacuole and release hydrolytic enzymes to destroy the bacterial cells.[1]
(c)Research has shown that vaccination programmes are cost effective and are very helpful in the prevention and control of TB. The programmes may be aimed at particular groups of people that are at a high risk of getting the disease, or they may be aimed at an entire population because the country has a high number of cases of TB. The Bacillus Calmette-Guérin (BCG) vaccine is freeze-dried and contains live, weakened (attenuated) Mycobacterium bovis. Apart from being cost effective, suggest and explain the advantages of using the BCG vaccine for the prevention and control of TB.[4]

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 (May/June 2024). The mark or mark type is shown in brackets.

[1] nucleolus ; manufactures ribosomal subunits from proteins and ribosomal RNA
[1] smooth endoplasmic reticulum ; R endoplastic synthesises triglycerides and other lipids
[1] pair of centrioles ; R centrosomes organise microtubules of the cell cytoskeleton
[1] roughly spherical organelle within the nucleus labelled as nucleolus
[1] minimum of one single membrane-bound tubular sac labelled as, smooth endoplasmic reticulum / smooth ER / SER R if dots (ribosomes) drawn and resembles RER
[1] two, short lines or cylinders, not parallel to each other labelled as (pair of) centrioles R if inside the nucleus
[1] endocytosis occurs / described; e.g. (macrophage cell surface) membrane, surrounds / AW, bacterial cells pseudopodia, surrounds / form round / AW, bacterial cell (alveolar) macrophage / phagocyte / (phagocytic) cell, envelops / engulfs, bacterial cells ;
[1] bacterial cells / bacteria / (bacterial) antigens, bind / attach/join/ AW, to (macrophage cell surface), receptors / membrane I binding to, macrophage / cell suggestion of (in alveolar space) opsonisation of /antibody binding to, bacterial cells
[1] membrane fusion / (phagocytic), vacuole pinches off / AW A vesicle for vacuole
[1] lysosomes / lysosome ; A lysosomal vesicles
[1] cells are replicating / AW (because live vaccine);
[1] high/increased / AW, levels of (non-self / foreign) antigen (because live vaccine);
[1] (so) strong / effective / good / AW, (primary) immune response; A described e.g. (T-/B-) memory cells are formed idea that memory cells present when Mycobacterium infects / AW secondary response occurs when Mycobacterium infects / AW
[1] provides (artificial) active immunity; R natural active immunity
[1] (so) boosters not needed (to build sufficient immunity);
[1] vaccine does not cause, disease / TB (because, weakened / attenuated) ; I doesn't show symptoms
[1] easy to, transport / store / deliver (because freeze-dried);
[1] AVP ;; e.g. effective against M. tuberculosis and M. bovis no / few / mild, side effects, so people not discouraged (from having vaccine) memory cells / immunity, (relatively) long-lived / long-lasting only need one dose (good immunity for most individuals) provides herd immunity (a consequential effect)