DP Chemistry (last assessment 2024)
Question 18N.3.hl.TZ0.17
| Date | November 2018 | Marks available | [Maximum mark: 3] | Reference code | 18N.3.hl.TZ0.17 |
| Level | hl | Paper | 3 | Time zone | TZ0 |
| Command term | Explain, Outline | Question number | 17 | Adapted from | N/A |
17.
[Maximum mark: 3]
18N.3.hl.TZ0.17
Opiates are strong analgesics.
(a)
Explain why diamorphine (heroin) crosses the blood–brain barrier more easily than morphine.
[2]
Markscheme
blood-brain barrier is hydrophobic/non-polar/made of lipids ✔
morphine has hydroxyl/OH «groups»/is more polar AND diamorphine has ester/ethanoate/OCOCH3/acetate «groups»/is less polar/is lipid soluble ✔
Accept “fats” for “lipid”.
Accept “alcohol/hydroxy” for “hydroxyl” but not “hydroxide”.
Accept “non-polar” for “less polar” in M2.
(b)
Outline the meaning of the bioavailability of a drug.
[1]
Markscheme
fraction/proportion/percentage of «administered dosage» enters blood/plasma/circulation ✔
Accept “fraction/proportion/percentage of «administered dosage» that reaches target «part of human body»”.
