Question 18N.3.sl.TZ0.12
| Date | November 2018 | Marks available | [Maximum mark: 7] | Reference code | 18N.3.sl.TZ0.12 |
| Level | sl | Paper | 3 | Time zone | TZ0 |
| Command term | Explain, Outline, State, Suggest | Question number | 12 | Adapted from | N/A |
The structure of penicillin is shown in section 37 of the data booklet.
State the internal bond angles in the β-lactam ring and the expected bond angles for the same atoms in an open structure.
[2]
Accept “109º”.
Explain how the open β-lactam ring kills bacteria.
[2]
«irreversibly» binds/bonds to enzyme/transpeptidase
OR
inhibits enzyme/transpeptidase «in bacteria» that produces cell walls
OR
prevents cross-linking of bacterial cell walls ✔
cells absorb water AND burst
OR
cells cannot reproduce ✔
Accept “reacts with” for “bonds to” for M1.
Do not accept “cell membrane” for “cell wall” for M1.
Accept “cells burst due to osmotic pressure” for M2.
Accept “bacteria” for “cells” for M2.
Outline one effect of over-prescription of penicillin.
[1]
Any one of:
leads to «bacterial» resistance «to antibiotics»
OR
makes antibiotics less effective
OR
increased side effects due to larger dosages/over time ✔
increases proportion of resistant bacteria ✔
destroys useful/beneficial bacteria
OR
destroyed bacteria replaced by more harmful bacteria ✔
resistant bacteria pass on their mutation to next generation ✔
damage to ecosystems ✔
Accept “superbugs such as MRSA develop” but superbug must be identified.
Accept “immune” for resistant but do not accept “tolerance”
State how the structure of penicillin can be changed to combat this effect.
[1]
«modify» side-chain ✔
Accept “«modify» R”.
Suggest why human cells are not affected by penicillin.
[1]
no cell walls
OR
humans do not have transpeptidase ✔