| Date | May 2016 | Marks available | 2 | Reference code | 16M.3.hl.TZ0.14 |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | Explain | Question number | 14 | Adapted from | N/A |
Question
Hemoglobin contains a heme group with an iron(II) ion.
Outline how the oxygen saturation of hemoglobin is affected by changes in the blood plasma.
Explain why foetal hemoglobin has a greater affinity for oxygen.
Markscheme
low CO2 level causes more oxygen to be bound to the heme
high pH causes more oxygen to be bound to the heme
low temperature causes more oxygen to be bound to the heme
organic phosphates/2,3-BPG/DPG can decrease affinity for oxygen
CO decreases saturation/binds to active site/acts as a competitive inhibitor
Accept reverse statements for mark.
Award [2] if the effects of CO2 AND pH are discussed in combination.
contains two gamma units «instead of the two beta units found in adults»
OR
differs in amino acid sequence «from the two beta units found in adults»
less sensitive to inhibitors/2,3-BPG/DPG
receives O2 from «partly deoxygenated» blood so can work at low pO2
Accept reverse statements for mark.
