A level Biology B · Edexcel 9BI0 · Topic 4E
Haemoglobin and oxygen transport
Key points
- Haemoglobin is a protein with four polypeptide chains, each with a haem group containing Fe that binds one O molecule.
- The oxygen dissociation curve is S-shaped: after the first O binds, the shape changes and the next ones bind more easily (cooperative binding).
- In the lungs (high partial pressure of O) haemoglobin loads and becomes almost fully saturated; in respiring tissues it unloads.
- Bohr effect: higher CO lowers pH, reducing haemoglobin's affinity for O and shifting the curve to the right, so more O is released where it is needed.
- Fetal haemoglobin has a higher affinity (curve to the left), so it takes O from the mother's blood.
- Myoglobin in muscle has a very high affinity and stores O; animals in low-oxygen environments have curves shifted left.
Topic notesPremium
Haemoglobin carries oxygen from the lungs to respiring tissues. Its value lies not just in binding oxygen but in letting it go in the right place, and the oxygen dissociation curve shows exactly how it does both.
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