| Date | May 2015 | Marks available | 2 | Reference code | 15M.3.hl.TZ2.18 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Explain | Question number | 18 | Adapted from | N/A |
Question
Morphine and its derivatives work by temporarily bonding to receptor sites in the brain, preventing the transmission of pain impulses.
Explain why the change in functional groups makes diamorphine (heroin) more potent than morphine.
Markscheme
ester group/diamorphine less polar / hydroxyl group/morphine more polar / diamorphine more soluble in non-aqueous systems/lipids/fats/fatty tissue / morphine less soluble in non-aqueous systems/lipids/fats/fatty tissue;
(ester group means) diamorphine crosses blood-brain barrier/into central nervous system/CNS/brain faster/more easily;
Award [1 max] for answers that correctly describe diamorphine/morphine but do not compare the two.
Examiners report
Many candidates described morphine (strong analgesic) rather than discussing an advantage of the drug. Most could also identify disadvantages, but sometimes referred to issues applicable to any substance, such as the problems of overdosing. The structural difference between morphine and diamorphine, and why this makes the latter more potent, were well known.
