DP Chemistry (last assessment 2024)
Question 19M.3.hl.TZ2.b(i)
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.hl.TZ2.b(i) |
| Level | hl | Paper | 3 | Time zone | TZ2 |
| Command term | Explain | Question number | b(i) | Adapted from | N/A |
b(i).
[Maximum mark: 2]
19M.3.hl.TZ2.b(i)
Hemoglobin contains heme groups with the porphyrin ring bound to an iron(II) ion.
A hemoglobin’s oxygen dissociation curve is shown.
Explain the shape of the curve.
[2]
Markscheme
sigmoid/S-shaped
OR
as oxygen binds to one active site, shape of other active sites change [✔]
affinity of other sites for oxygen increases/ability to bind oxygen is increased by initial binding of oxygen
OR
cooperative binding [✔]
Note: Accept description of sigmoid/S-shaped curve if not stated for M1.
Examiners report
Many candidates managed one mark by describing the graph and stating that the affinity of other sites for oxygen increases/cooperative bonding. Several candidates missed that it was a sigmoid/S-shaped curve.
