Question

Bulk of carbon-dioxide $\left(C{O}_2\right)$ released from body tissues into the blood is present as

• A. Free $C{O}_2$ in blood plasma
• B. Bicarbonate in blood plasma and RBCs
• C. Carbamino-haemoglobin in RBCs
• D. $70\%$ carbamino-haemoglobin and $30\%$ as bicarbonate

Answer 1

The correct option is B

Bicarbonate in blood plasma and RBCs

The correct option is B

Explanation of the correct option:

1. The larger part of carbon dioxide released from body tissues into the blood is transported as a bicarbonate ion in blood plasma and RBCs i.e.,$61\%$.
2. In the lungs, the diffusion of oxygen into the blood triggers reactions.
3. The oxygen reacts with attaches with hemoglobin.
4. This oxygenation reaction with hemoglobin forms excess ${\mathrm{H}}^{+}$ ions which react with bicarbonate ion$\left({{\mathrm{HCO}}_3}^{-}\right)$ and produce carbonic acid$\left({\mathrm{H}}_2{\mathrm{CO}}_3\right)$.
5. When $C{O}_2$ diffuses from tissues into the blood then it is acted upon by the enzyme carbonic anhydrase.
6. The carbonic acid gets decomposed into $C{O}_2$ which diffuses out of the blood.

Explanation of the incorrect options:

Option A:

The gases cannot be transferred independently inside the body, thus $C{O}_2$ requires a carrier for transportation.

Option C:

Carbaminohemoglobin is a compound of hemoglobin and carbon dioxide and is one of the forms in which carbon dioxide exists in the blood. But not that abundant.

Option D:

$70\%$ carbamino-hemoglobin and $30\%$ as bicarbonate is carried by blood but in bulk, bicarbonate is formed from $C{O}_2$ in tissue.

Final Answer: Bulk of carbon-dioxide $\left(C{O}_2\right)$ released from body tissues into the blood is present as Bicarbonate in blood plasma and RBCs.