| Date | November 2014 | Marks available | 3 | Reference code | 14N.3.sl.TZ0.16 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Explain | Question number | 16 | Adapted from | N/A |
Question
The first commercially available antibiotic came from a class of compounds known as the penicillins.
Explain how penicillins work and why it is necessary to continually modify the side-chain.
Markscheme
penicillins interfere with (enzymes involved with) development of cell wall/(cross-link) structure of bacteria;
(due to damage) cells absorb water (by osmosis) and burst / OWTTE;
modifying side-chain overcomes resistance (by bacteria) / OWTTE;
Examiners report
In (b) the most common mistake seen was claims that penicillin breaks down cell walls. This is totally incorrect – penicillin does not break down existing cell walls – it only interferes with the production of new ones. Many candidates also did not mention the fact that due to damage cells absorb water and burst. Most knew that modification of the side-chain overcomes resistance by bacteria.
