Question

The sigmoid shape of the dissociation curve is because

• A. Binding of oxygen to haemoglobin. As the first oxygen molecule binds to haemoglobin, it increases the affinity for the second molecule of oxygen to bind. Subsequently, haemoglobin attracts more oxygen.
• B. The curve shows the equilibrium of oxyhaemoglobin and haemoglobin
• C. In the lungs,the partial pressure of oxygen is high
• D. Tissues have a low oxygen concentration

Answer 1

Answer: (A)

Binding of oxygen to haemoglobin. As the first oxygen molecule binds to haemoglobin, it increases the affinity for the second molecule of oxygen to bind. Subsequently, haemoglobin attracts more oxygen.

Haemoglobin molecule can bind to four oxygen molecules reversibly. The dissociation curve is the curve that results from the interaction of oxygen molecules with haemoglobin molecule. It indicates the oxygen saturation and partial pressure of oxygen in the blood. The binding of the first molecule is difficult. As the first oxygen molecule binds to haemoglobin, it increases the affinity of the haemoglobin molecules for the second molecule of oxygen to bind. Subsequently, haemoglobin attracts more oxygen and hence, the curve is sigmoid shape or S-shape.

Thus, the correct answer is 'Binding of oxygen to haemoglobin. As the first oxygen molecule binds to haemoglobin, it increases the affinity for the second molecule of oxygen to bind. Subsequently, haemoglobin attracts more oxygen'.