Question

What is true about RBCs in humans?
A) They do not carry $C{O_2}$ at all
B) They carry about 20-25% of$C{O_2}$
C) They transport 99% of$C{O_2}$
D) They transport about of oxygen only and the rest 20% of it is transported in dissolved state in blood plasma

Answer 1

The red blood cells also known as erythrocytes are an important component of blood. The life-giving gas of Oxygen which is essential for survival reaches to each cell through RBC only. On the other hand, there are three ways of $C{O_2}$ transfer in the blood. They are dissolved in solutions, bound to plasma proteins or hemoglobin or changed to bicarbonates.

Complete answer:

The primary function of RBC includes the transportation of oxygen from the heart to the rest of the body and also to collect the deoxygenated blood back to the heart. Hence it would be wrong to say that RBCs don’t carry $C{O_2}$at all.
The 70% of $C{O_2}$is transported as bicarbonates and the rest 7% approximately is transported by plasma proteins. Hence, it can be said that RBC do not transport 99% of $C{O_2}$.
The RBC transport about 97% of Oxygen and the rest 7% is transported by Plasma. Hence, the statement that RBC transport about 80% of oxygen only and the rest 20% of it is transported in dissolved state in blood plasma is incorrect.
So, we can say that option B is right here. The RBC transports at least 20-25% of $C{O_2}$as the rest proportion is transported in the form of bicarbonates or through plasma proteins.

Note: As we can see that 70% of $C{O_2}$is carried as bicarbonates. A typical human red blood cell has a disk diameter of approximately $6.2 - 8.2\,\mu m$. It is considerably much smaller than most other human cells.