Breathing and Exchange of Gases Question 33
33. Oxygen dissociation curve of haemoglobin is
(a) Sigmoid
(b) Hyperbolic
(c) Linear
(d) Hypobolic
Show Answer
Answer : a
Hints & Solution
(a) It is the relationship between the percentage saturation of haemoglobin (by volume) in the blood and the oxygen tension (partial tension) $PO_2$ of the blood. It is usually a sigmoid curve. Haemoglobin molecules can bind up to four oxygen molecules in a reversible manner. The shape of the curve results from the interaction of bound oxygen molecules with incoming molecules. The binding of the first molecule is difficult. However, this facilitates the binding of the second and third molecules, and it is only when the fourth molecule is to be bound that the difficulty increases, partly as a result of crowding of the haemoglobin molecule, partly as a natural tendency of oxygen to dissociate. The $O_2-Hb$ dissociation curve is a sigmoidal curve that represents the relationship between $O_2$ concentration and the percentage saturation of $Hb$. As the concentration increases from about $90 %$ there is a significant plateau in the curve, which has several important biological repercussions.
