| Date | May 2017 | Marks available | 1 | Reference code | 17M.3.sl.TZ1.18 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Outline | Question number | 18 | Adapted from | N/A |
Question
Medicines have a variety of different effects on the body and act at the molecular level.
Morphine and codeine are strong analgesics. Their structures are given in section 37 of the data booklet.
Dose response curves are determined for each drug.
Outline the significance of range “a”.
Suggest the type of reaction used to convert morphine to codeine.
State and explain the action of opiates as painkillers.
Markscheme
«measures» therapeutic window/margin «of a drug»
OR
range of doses that produce a therapeutic effect without causing toxic effects
Accept “difference between ED50/minimum effective/therapeutic dose «for 50% of population» AND TD50 /toxic dose «for 50% of population»”.
Do not accept “therapeutic index”.
Do not accept “lethal/fatal dose” as this is not LD50.
[1 mark]
«nucleophilic» substitution/SN
Accept “methylation”.
[1 mark]
work directly on opioid/pain receptors «in brain»
suppress pain impulses in brain/CNS
resemble endorphins/enkephalins/natural chemical painkillers «produced in the brain and spinal cord»
Do not award mark for “resemble hormones”.
[2 marks]
