Question

Haemoglobin (Hb) transports oxygen from lungs to tissues. The partial pressure of oxygen in lungs is different from that in tissue. Each Hb can bind up to four oxygen molecules. Suppose we have an equal number of Hb and oxygen molecules and all the oxygen molecules are in bound form. Then, Which of the following is TRUE ?
A. Almost all the Hb molecules have one bound oxygen molecule.
B. Nearly half to all the Hb molecules are each bound to two oxygen molecules.
C. Nearly one-fourth of all the Hb molecules are bound to four oxygen molecules each.
D. Most of the Hb molecules have one bound oxygen molecule each, the rest either have no bound oxygen or have two or more bound oxygen molecules.

Answer 1

Lungs are involved in the process of respiration in which the oxygen gas is transported through the Hb to all the tissues as oxygen is partially soluble on blood and depends on the heme group of the Hb molecule to be carried to different parts of the body.

Complete Answer:
Let us analyse the options to find the correct answer.
Option A: So if we have four molecules of each oxygen and Hb. Then, one Hb molecule is bound to one oxygen and thus isn’t fully saturated. Therefore, this is the incorrect option.

Option B: If we have four molecules of oxygen and Hb. Then, two molecules of Hb are bound to two molecules of oxygen each leaving two molecules of Hb unbound. Therefore, this is the incorrect option.

Option C: If one Hb molecule binds to four oxygen molecules. If we consider there are four oxygen and four Hb molecules then, one Hb molecule binds to four oxygen molecules and three Hb molecules remains unbound. Thus, one-fourth of the Hb is bound to four molecules of oxygen each. Therefore, this is the correct option.

Option D: If we have four molecules of oxygen and Hb, any combination (unbound Hb, Hb bound to one oxygen, Hb bound to more oxygen) remains non-functional. Therefore, this is the incorrect option.

Thus, the correct option is C) Nearly one-fourth of all the Hb molecules are bound to four oxygen molecules each.

Note: Hb saturation is said to be 100% if all the Hb is bound to four oxygen each. In normal individuals nearly 95-99% of the Hb is saturated with oxygen.