| Date | May 2017 | Marks available | 1 | Reference code | 17M.3.hl.TZ1.16 |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Outline | Question number | 16 | Adapted from | N/A |
Question
Biological pigments include a variety of chemical structures with diverse functions.
The graph shows the conversion of hemoglobin to oxyhemoglobin.
Hb(aq) + 4O2(g) \( \rightleftharpoons \) Hb(O2)4(aq)
The partial pressure of oxygen gas, p(O2) is proportional to its concentration.
Explain the shape of the curve at low oxygen partial pressure up to about 5 kPa.
Sketch a graph on the axes above to show the effect of decreasing pH on the binding of oxygen to hemoglobin (the Bohr Effect).
Outline the effect of decreasing pH on the oxygen saturation of hemoglobin.
Markscheme
binding of O2 «to one active site» affects shape of Hb/other active sites
OR
binding of one O2 «molecule» affects binding of other O2 «molecules»
increasing affinity of Hb to O2
OR
enhanced binding of «further» O2 «molecules»
OR
cooperative binding
[2 marks]
sketching right shift of curve on graph
[1 mark]
decreases «oxygen saturation»
Accept “hemoglobin binds to O2 with less affinity".
[1 mark]
