Haemoglobin adaptations depend on reversible gas binding, cooperative oxygen loading and affinity differences between adult haemoglobin, foetal haemoglobin and altitude-adapted forms.
Coverage 2018–2025 · Updated 15 Jul 2026
Haemoglobin binds oxygen reversibly in lungs and releases it in tissues, with its subunits enabling efficient loading and unloading.
In the lungs, high oxygen partial pressure favors binding. In respiring tissues, lower oxygen and altered conditions favor release, so haemoglobin transports rather than permanently stores oxygen.
Interpret a binding claim by checking: oxygen partial pressure; affinity; loading site; unloading tissue. These conditions change along the circulation.
Blood leaving the lungs carries more oxyhaemoglobin than blood arriving from oxygen-consuming muscle because the lungs provide a higher oxygen partial pressure.
High haemoglobin affinity is not always best: oxygen must also be released where cells need it.
This objective is assessed through structured response, commonly using Outline / Describe / Suggest.
Outline / Describe / Suggest
Build the answer around this relationship: Oxygen binds reversibly to haem groups containing iron in haemoglobin.
Describing foetal haemoglobin as having lower affinity instead of a left-shifted, higher-affinity curve.
Representative question
Suggest how changes in hemoglobin could help humans become better adapted to living at high altitude.
Haemoglobin increases oxygen transport because oxygen is poorly soluble in plasma. Reversible and cooperative binding allow loading at high pO2 and unloading at low pO2. High carbon dioxide lowers pH and causes the Bohr shift, reducing affinity and promoting oxygen release in active tissues. Dissociation curves show these changes through sigmoid shape and left/right shifts.
