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Define oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern ? 

Answer

Oxygen dissociation curve is the sigmoid curve obtained when the percentage saturation of haemoglobin with O2 is plotted against the partial pressure of oxygen pO2.  It helps in the study of the effect of factors like pCO2, H+ concentration etc. on binding of oxygen with haemoglobin. What is oxygen dissociation curve ?
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Define oxygen dissociation curve. Can you suggest any reason for its sigmoidal pattern ? 

The binding of oxygen to haemoglobin is in such a way that the binding of the first oxygen oxygen molecule binds to the haemoglobin, it increases the affinity for the second molecule of oxygen to bind. Subsequently, haemoglobin attracts more oxygen and this gives the curve a sigmoid shape.