A-LevelBiologyGas exchange9700/12 · Oct/Nov 2025 · Q341 Mark
The diagram shows the Bohr shift in actively respiring cells. [Graph showing percentage saturation of haemoglobin with oxygen against partial pressure of oxygen/kPa, with curves L and M] What causes the shift from L to M?
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
ACarbonic acid dissociates to release protons that bind to oxyhaemoglobin, affecting the conformation of haemoglobin to reduce its affinity for oxygen.
BHydrogencarbonate ions produced by carbonic anhydrase alter the charge of oxyhaemoglobin, reducing its ability to bind oxygen.
CHydrogen ions combine with chloride ions in tissue fluid to produce hydrochloric acid, distorting oxyhaemoglobin and causing it to lose bound oxygen.
Dlow concentration of oxygen in actively respiring cells causes oxyhaemoglobin to release oxygen more quickly down the concentration gradient.
✓ Correct answer
A: Carbonic acid dissociates to release protons that bind to oxyhaemoglobin, affecting the conformation of haemoglobin to reduce its affinity for oxygen.
Practise more questions on this topic
Oracle Prep sorts past-paper questions by topic, so you can drill Gas exchange and see which topics are most likely to come up next.
Sign up free →