A-LevelBiologyImmunity9700/21 · Oct/Nov 2019 · Q211 Marks

Fig. 2.1 is a transmission electron micrograph showing the bacterial pathogen that causes tuberculosis (TB). [Figure 2.1]

(a)(i)Name the pathogen shown in Fig. 2.1 that causes TB.[1]
(a)(ii)The World Health Organization (WHO) introduced a strategy in 2015 to end the global TB epidemic. An important part of the strategy is to: • identify people at risk of becoming infected with TB • use methods to prevent transmission of TB. The BCG vaccination is one method of prevention recommended for use in countries where TB is common. The BCG vaccine contains a non-pathogenic, living form of the microorganism that causes TB. Complete Table 2.1 by using a tick (✔) to identify the type of immunity that develops in a person who has been given the BCG vaccination. [Table 2.1][1]
(b)Rifampicin is one of the antibiotics used to treat TB. Rifampicin inhibits RNA polymerase in bacterial cells by binding to a site other than the active site. This prevents polypeptide synthesis.
(b)(i)Suggest and explain how rifampicin prevents polypeptide synthesis in bacterial cells.[3]
(b)(ii)Some bacteria have developed resistance to rifampicin. However, they are still susceptible to the other antibiotics that can be used to treat TB. Multi-drug resistant bacteria have developed resistance to at least two drugs, including rifampicin. WHO collects data from all countries on the number of cases of TB caused by rifampicin-resistant bacteria (RR-TB) and multi-drug resistant bacteria (MDR-TB). Fig. 2.2 shows the reported number of cases of TB between 2009 and 2013. [Figure 2.2] Describe the trend shown by the data in Fig. 2.2.[2]
(b)(iii)Explain how resistance to drugs such as rifampicin develops.[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 (Oct/Nov 2019). The mark or mark type is shown in brackets.

[1] (a)(i) Mycobacterium tuberculosis or Mycobacterium bovis ;
[1] (a)(ii) artificial active immunity ✔ ;
[3] (b)(i) three from changes the tertiary structure / shape of active site, of, enzyme / RNA polymerase ; active site no longer complementary to, RNA nucleotides / substrate ; AW RNA nucleotides not joined / mRNA not synthesised; A transcription does not occur translation prevented ; A described, I polypeptide / protein synthesis prevented AVP; ref. to other roles of RNA polymerase not occurring, e.g. does not bind to DNA, double helix does not unwind
[2] (b)(ii) two from (from 2009 to 2013) overall increase in number of cases (of RR-TB and MDR-TB); use of data to support overall trend ; ref. to large increase between 2011 and 2012/2013 or very little change between 2010 and 2011;
[4] (b)(iii) four from overuse of, antibiotics / rifampicin or example of over use; e.g. taking for viral infection, over prescribing for bacterial infection people not completing course of antibiotics; reservoir of bacteria remains ; ref. to mutation; any detail of the mutation; e.g. protein produced has a changed binding site bacteria with resistance, survive / selected for or only bacteria sensitive to antibiotic are, killed / selected against; A antibiotic acts as a selection pressure bacteria reproduce and pass on, gene / allele, for resistance to offspring or vertical (gene) transmission ; (alleles for resistance to antibiotics transferred by) horizontal (gene) transmission / described ; frequency of resistance, gene / allele, increases in the bacterial population ;