A-LevelBiologyInfectious diseases9700/21 · Oct/Nov 2021 · Q313 Marks

Cholera is an infectious disease caused by the bacterial pathogen Vibrio cholerae. (a) Describe how V. cholerae is transmitted from an infected person to an uninfected person.

(a)Describe how V. cholerae is transmitted from an infected person to an uninfected person.[2]
(b)V. cholerae releases a toxin called choleragen. Choleragen is a protein molecule made up of six polypeptides (subunits). Fig. 3.1 is a ribbon diagram of a molecule of choleragen. [Figure 3.1] Describe what is shown by the part of the molecule labelled T.[3]
(c)(i)Vaccination can be used to prevent the spread of cholera. The vaccine used contains part of the choleragen molecule and also contains dead cells of V. cholerae. Phagocytes play an important role in the immune response to a vaccine. Phagocytes contain many lysosomes. Describe the function of lysosomes in phagocytes.[2]
(c)(ii)Suggest the advantage of having a vaccine that includes dead cells of V. cholerae and part of the choleragen molecule.[2]
(d)The World Health Organization states that most cases of cholera can be treated with oral rehydration therapy. To reduce the risk of antibiotic resistance developing, antibiotics are only recommended for the most serious cases. Discuss the consequences of the development of antibiotic resistance in V. cholerae.[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 2021). The mark or mark type is shown in brackets.

[2] one mark for infected person with contaminated faeces faeces/sewage, contaminates, (drinking) water / cooking utensils / vegetable plots / crops / food;
one mark for uninfected person drinking contaminated water / eating food washed in contaminated water ;
R infected food or water;
A faecal-oral route for two marks
[3] any three from: secondary structure ;
alpha / α, helix ;
bonding hydrogen bonding;
further detail;
e.g. between NH and CO of different amino acids four, amino acids / places, ahead hydrogen of the NH and oxygen of the CO
[2] any two from: break down / digest / hydrolyse / AW, pathogen / foreign material / AW;
ref. to containing hydrolytic / digestive / named, enzymes ; A hydrolases
fuse with the, phagosome / phagocytic vacuole / AW ;
[2] any two from: cells are dead so cannot, cause disease / reproduce / AW ;
only part of a choleragen molecule, so no toxic effect ;
recognised by / trigger clonal selection of, more than one type of B-lymphocyte ;
stimulates production of different antibodies ;
stimulates the production of more than one type of memory cell / AW ;
ref. to immune system cells can respond to bacterial cells and the toxin produced ;
AVP; e.g. different antigens on the surface of the cells
[4] any four from: (resistant) (Vibrio cholerae)is not killed by the antibiotic ;
A can still reproduce
inability to treat people with cholera using antibiotics;
prolonged periods of illness;
(so) increased risk of spread / AW ;
increased death rate from cholera ;
transfer of antibiotic resistance (alleles) to, other species of bacteria / other strains of V.cholerae ;
development of multiple resistance in other species of bacteria ;
inability to treat other bacterial diseases ;
increased death rate from other bacterial diseases ;
need to research alternative antibiotics ;
AVP;