| Date | November 2018 | Marks available | 2 | Reference code | 18N.3.sl.TZ0.12 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | State | Question number | 12 | Adapted from | N/A |
Question
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.
Explain how the open β-lactam ring kills bacteria.
Outline one effect of over-prescription of penicillin.
State how the structure of penicillin can be changed to combat this effect.
Suggest why human cells are not affected by penicillin.
Markscheme
Accept “109º”.
«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.
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”
«modify» side-chain ✔
Accept “«modify» R”.
no cell walls
OR
humans do not have transpeptidase ✔
Examiners report
Syllabus sections
- 17N.3.sl.TZ0.18b: State the method of drug administration that gives the maximum bioavailability.
-
17M.3.sl.TZ2.15b.ii:
Compare, giving a reason, the bioavailability of soluble aspirin with aspirin.
-
20N.3.sl.TZ0.12:
Consider the following antacids:
Show that antacid X is more effective, per tablet, than antacid Y.
- 18N.3.sl.TZ0.13c: Outline the meaning of the bioavailability of a drug.
- 18N.3.hl.TZ0.17b: Outline the meaning of the bioavailability of a drug.
-
18M.3.sl.TZ2.15:
Drug testing is necessary to determine safe and effective doses.
Distinguish between the lethal dose (LD50) and the toxic dose (TD50).
-
19M.3.hl.TZ1.22b:
Suggest a reason for using a phosphate salt of oseltamivir in oral tablets.
-
19M.3.sl.TZ1.17a(ii):
Suggest a reason for using a phosphate salt of oseltamivir in oral tablets.
-
17M.3.sl.TZ2.18b:
Suggest one ethical consideration faced by medical researchers when developing medications.
- 19N.3.hl.TZ0.21b: Experimental research on both animals and humans contributes to the development...
-
18M.3.sl.TZ1.13b.i:
State what is meant by the bioavailability of a drug.
-
19M.3.hl.TZ2.21a:
Distinguish between therapeutic window and therapeutic index in humans.
Therapeutic window:
Therapeutic index:
-
17N.3.sl.TZ0.18a:
Outline the difference between the therapeutic index in animal studies and the therapeutic index in humans.
-
17M.3.sl.TZ1.18a:
Dose response curves are determined for each drug.
Outline the significance of range “a”.
-
19M.3.sl.TZ2.14a:
Distinguish between therapeutic window and therapeutic index in humans.
Therapeutic window:
Therapeutic index:
-
20N.3.sl.TZ0.11d:
Comment on the risk of overdose when taking aspirin as an analgesic, referring to the following values, for a person weighing :
Minimum therapeutic dose
Estimated minimum lethal dose
-
20N.3.hl.TZ0.15d:
Comment on the risk of overdose when taking aspirin as an analgesic, referring to the following values, for a person weighing :
Minimum therapeutic dose
Estimated minimum lethal dose
