Question

If haemoglobin is 75% saturated, then how many oxygen molecules are combined with haemoglobin?

• A. 3
• B. 2
• C. 3/2
• D. 1

Answer 1

The correct option is A 3

RBC is a red blood cell which contains haemoglobin protein. Each haemoglobin has 4 globins and 4 heme groups. Each heme group contains iron pigments in it. The oxygen and carbon dioxide alternatively binds to haemoglobin in a reversible manner.

$\underset{\underset{\text{(uncombined or deoxygenate haemoglobin)}}{\text{Reduced haemoglobin}}}{\text{Hb}}+O_2\rightleftharpoons \underset{\underset{\left(\text{combined or oxygenated haemoglobin}\right)}{\text{Oxyhaemoglobin}}}{Hb{O}_2}$
Fig. Haemoglobin binds to oxygen to form oxyhaemoglobin.

Oxygen binding to haemoglobin is expressed as percentage.
1 haemoglobin+1 $O_2$ molecule = haemoglobin is 25% saturated
1 haemoglobin+2 $O_2$ molecule = haemoglobin is 50% saturated.
1 haemoglobin+3 $O_2$ molecule = haemoglobin is 75% saturated.
1 haemoglobin+4 $O_2$ molecule = haemoglobin is 100% saturated.