A-LevelBiologyInfectious diseases9700/21 · May/June 2017 · Q611 Marks
Cholera bacteria release the toxin, choleragen, when they are in the intestine. (a) (i) Name the bacterium that is the pathogen of cholera. (ii) Describe the way in which cholera is transmitted from an infected person to an uninfected person. Gangliosides are glycolipids that bind choleragen. These glycolipids are found on many cell surface membranes. When choleragen is released from the bacteria in the intestine, it binds to gangliosides on epithelial cells and enters these cells as shown in Fig. 6.1. [Figure 6.1]
- (a)(i)Name the bacterium that is the pathogen of cholera.[1]
- (a)(ii)Describe the way in which cholera is transmitted from an infected person to an uninfected person.[2]
- (b)Suggest how choleragen interacts with gangliosides on intestinal epithelial cells.[2]
- (c)Name the process by which choleragen enters the intestinal epithelial cell as shown in Fig. 6.1.[1]
- (d)Suggest and explain the likely consequences on the intestinal epithelial cells of the loss of chloride ions through the channel proteins.[2]
- (e)Health authorities recommend that antibiotics, such as tetracycline, are only to be used for treating people with severe cases of cholera. Explain why it is recommended that antibiotics should not be given to people with mild cases of cholera or to protect people from cholera.[3]
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 2017). The mark or mark type is shown in brackets.
- Vibrio cholerae ;
- faecal-oral route ;;
- description of faecal/oral route
- infected person
- faeces/sewage / stool, contaminating (drinking) water R (human) waste unqualified
- or poor hygiene so transferring, faecal material / sewage, onto utensils / food / AW
- or defaecating / putting sewage, onto vegetable plots ;
- or flies in contact with contaminated faeces landing on food and contaminating / AW
- uninfected person
- eating contaminated food / using contaminated utensils
- or drinking contaminated water ;
- 1 ganglioside is the receptor for choleragen ;
- 2 choleragen is complementary to ganglioside ;
- 3 any interaction between molecules; e.g. (hydrogen / ionic) bonding
- endocytosis; A phagocytosis / pinocytosis
- 1 loss of water / dehydration;
- 2 by osmosis;
- 3 (water moves out) down water potential gradient / from high to low water potential / high Ψ to low Ψ;
- 4 Loss of cations / positively-charged ions (as well as chloride ions) ;
- 5 change in potential (difference) / change in charge across membrane ;
- 6 AVP; e.g. disruption of absorption (of products of digestion / vitamins / mineral ions) disruption of digestion
- 1 rehydration therapy, is effective / can treat cholera / reduces death rate ;
- 2 any detail; e.g. solution of glucose and salts
- 3 antibiotic is a selection pressure / described ;
- 4 ref. to, antibiotic/tetracycline, resistance ;
- 5 ref. to, vertical transmission / horizontal transmission, of resistance ; A described, A transfer for transmission
- 6 antibiotics will become, ineffective / less effective / AW ;
- 7 keep antibiotics for use 'as last resort'; AW
- 8 ref. to cost;
- 9 antibiotics kill gut bacteria ;
- 10 idea that disrupts functions of digestive system;
- 11 AVP; e.g. antibiotics going into the environment / food chain antibiotics can cause mutation decreases need to develop new drugs prevents development of active immunity idea of transmission between bacterial species plasmids with resistance genes
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