Draw a circle round a glycosidic bond in Fig. 4.2.
In aquatic habitats, Vibrio cholerae can live on the surface of copepods. V. cholerae releases enzymes to hydrolyse chitin to its N-acetylglucosamine monomers. These can be broken down to provide carbon, nitrogen and a source of energy. Draw the monomer formed when chitin is hydrolysed by V. cholerae.
V. cholerae is a pathogen that causes cholera. Scientists investigated the transmission of V. cholerae in groups of people living in an area with a high number of cholera cases. Some families in this area filtered their water through several layers of folded fabric from old clothing. The folded fabric traps particles and organisms larger than $20\,\mu\text{m}$. The scientists counted the cholera cases in families that filtered their water through folded fabric and compared them with the number of cases recorded in families that did not filter their water through the folded fabric. The results are shown in Fig. 4.3. Suggest possible explanations for the results shown in Fig. 4.3.
The World Health Organization (WHO) recommends using an oral cholera vaccine (OCV) to protect people living in an area where a cholera outbreak has happened. People who receive an OCV and change their behaviour are less likely to develop a serious case of cholera. Describe one change in behaviour that a person can make, other than purifying water, to help prevent a serious case of cholera.
The antibiotic tetracycline is used to treat cholera. However, some bacteria that cause cholera have evolved resistance to this antibiotic. Scientists have reported that resistant bacteria have an extra protein in their cell surface membrane. This protein has been found to use ATP. Suggest how the presence of this protein in the cell surface membrane gives V. cholerae resistance to tetracycline.
For some vaccines, infection by the specific pathogen may not produce an effective secondary immune response. The antibodies that are produced do not act on the pathogen. This is called immune evasion. Resistance in bacteria to antibiotics evolves more often than immune evasion. Suggest why bacteria evolve resistance to antibiotics more frequently than vaccines lose their effectiveness in protecting against bacterial pathogens.