Explain the oxyhaemoglobin dissociation curve and the factors that may alter it.

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College Answer

Marks were awarded for an appropriate curve with values, an explanation of the nature of 
positive cooperatively and notes on those factors causing changes in the p50 or "shifts” in the 
curve. 
Most candidates were able to provide the required sigmoid shaped curve with appropriate key 
value points (p50, venous and arterial points). Better candidates were able to identify p50 as a 
measure of avidity or affinity for oxygen and commented on T- Tense and R- Relaxed states, 
the role and production of 2,3 DPG , binding to the beta chains (nature of the lack effect on 
foetal haemoglobin). Describing the mechanisms associated with factors shifting the curve and 
commenting on changes in oxygen content over the steep and flatter parts of the curves gained 
additional marks. Candidates are reminded to answer the question asked - no marks were 
awarded for a description of dissolved oxygen delivery. Some answers confused the Bohr and 
Haldane effects.