Oxygen Dissociation Curve

Question 1

Why do the lungs have a high pO2?

Answer 1

• The lungs have a high pO2 so that the Hb molecules have a high affinity for oxygen.
• Therefore oxygen binds to the haemoglobin.
• Hb becomes almost 100% saturated with oxygen.

Question 2

Why do muscles have a low pO2?

Answer 2

• Muscle tissues have a low pO2 dues to respiration taking place at the cells.
• Therefore, Hb has a low affinity for oxygen, so oxygen dissociates from Hb.
• Therefore, Hb unloads O2 which diffuses into the respiring muscle tissue cells.

Question 3

What does the oxygen dissociation curve show?

Answer 3

• Shows the relationship between how much oxygen is carried by Hb in red blood cells and the concentration of oxygen in the surrounding environment (eg. Lung tissue and muscle tissue).
• Affinity is lowering when the pO2 is lowering, so the % saturation of haemoglobin decreases as oxygen is dissociated from the Hb.

Question 4

Why does the S-shape curve provide evidence for co-operative binding?

Answer 4

At low pO2 levels, there is a small increase in % saturation of Hb; the rapid rise in % saturation shows that it gets easier for O2 molecules to bind to O2.