A-LevelBiologyInfectious diseases9700/23 · Oct/Nov 2018 · Q59 Marks

The bacteria that cause tuberculosis (TB) can be found in many parts of the body including the lungs.

(a)(i)State the name of the bacterium that causes TB.[1]
(a)(ii)The presence of the pathogen in the lungs attracts phagocytes to the area of infection. The phagocytes release elastase, which digests elastin. Many people with TB feel tired all the time. Suggest and explain how the effect of phagocytes on tissues in the lungs leads to people feeling tired all the time.[3]
(b)Discuss the biological factors and social factors that make TB a difficult disease to control.[5]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

[(a)(i)] Mycobacterium, tuberculosis / bovis ;
[(a)(ii) any three from]
[1] phagocytes / macrophages / neutrophils / elastase, breaks down / weakens, alveolar walls ;
[2] (reduced elastin so) alveoli cannot stretch and recoil / alveoli overstretch ;
[3] alveoli burst / one large air sac formed ;
[4] surface area (for gas exchange) is reduced ;
[5] less oxygen absorbed by blood / reduced oxygen supply (to tissues) / not enough oxygen for (aerobic) respiration / AW ;
[(b) R cost]
[(b) any five from]
[1] Transmission ; e.g. aerosol / droplet, infection I airborne A lack of pasteurised milk overcrowded, housing / living conditions / AW migration / travel, from areas with high rates of TB reservoir of infection in people not, diagnosed / not treated
[2] HIV / immunodeficiency ; e.g. infection with HIV may activate (dormant) TB (pathogen) immunodeficiency / AW, makes more people susceptible to TB intravenous drug taking increases risk of, immunodeficiency / HIV
[3] Diagnosis is difficult ; e.g. TB (pathogen) remains dormant / symptomless carriers limited access to health care for diagnosis / AW idea that contact tracing is difficult
[4] Treatment ; e.g. treatment is long term / treatment may not start early enough people may not finish the course of treatment limited access to health care for treatment
[5] Acquired resistance ; e.g. bacterium / TB (pathogen), develops resistance to, antibiotic(s) / drug(s) multi-drug resistance / MDR-TB / XDR-TB
[6] Vaccination ; e.g. vaccine may not always be effective in providing protection difficult to achieve herd immunity concerns / misconceptions, about vaccination limited access to vaccination (programmes) poor (immune) response in people who are malnourished poor thermostability of vaccine
[7] Education ; e.g. limited education / low awareness, about prevention for general population limited education / low awareness, for health care professionals