Question

The Sigmoid shape of dissociation curve is because
A. Binding 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 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

Hint: The oxyhaemoglobin dissociation curve explains the relation between the partial pressure and the oxygen saturation. As the oxygen molecule binds with the haemoglobin, its affinity for oxygen increases per binding.

Complete Answer:
- In the dissociation curve, the partial pressure of oxygen is taken on the X-axis and the oxygen saturation is taken on the y-axis. It helps us in understanding how our blood carries and releases oxygen. It determines the oxygen affinity of haemoglobin.
- The standard dissociation curve is sigmoid shape or S-shaped. This is due to the haemoglobin. The haemoglobin travels from the lungs to the tissues due to which the partial pressure becomes high.
- The surrounding pH value decreases and the amount of $CO_2$ that it reacts with increases. As the first oxygen molecule binds with the haemoglobin, the affinity for the second molecule increases as a result of which more oxygen binds with the haemoglobin.

Thus the correct answer is (A).

Note: Several factors affect the affinity of haemoglobin to oxygen which affects the oxygen-haemoglobin dissociation curve.
- pH
- Temperature
- Carbon dioxide
- Carbon monoxide