Question

Maximum of $CO_2$ produced by our body is transported
(A) As bicarbonates
(B) As carbonates
(C) Attached to haemoglobin
(D) Dissolved in blood plasma

Answer 1

Carbon dioxide is produced in our body as a by-product of respiration. Carbon dioxide $(C{O_2})$is mostly transported by the blood in the body. Apart from that, around $20 - 25\%$ of $(C{O_2})$is transported by the red blood cells (RBC's) while $70\%$ of $C{O_2}$ is transported in other forms.

Complete answer:
Generally, there are three approaches through which the molecules of $C{O_2}$are carried to the lungs from the corresponding body tissues with the help of blood. These three approaches include

Dissolving of $C{O_2}$directly in blood, binding of $C{O_2}$ with the haemoglobin and carrying of $C{O_2}$ in the form of bicarbonate ions. There are various properties of $C{O_2}$, present in the blood, which significantly affects its transportation. Some of these properties are, firstly $C{O_2}$ is more and easily soluble in blood rather than oxygen.

Secondly, $C{O_2}$ could easily bind with the plasma proteins or could go into RBCs and bind with the haemoglobin. Through this method, almost$10\%$ of $C{O_2}$ is transported. Moreover, when $C{O_2}$ combines with the haemoglobin, a new molecule is formed known as carbaminohemoglobin. The process of binding of $C{O_2}$ with the haemoglobin is reversible. As a result, it arrives in the lungs, the $C{O_2}$ liberally detaches from the haemoglobin and gets released from the body.

Thirdly, most of the $C{O_2}$ molecules i.e. almost $85\%$ are transported as bicarbonates in the body. In the bicarbonate based buffer system, $C{O_2}$is diffused within the RBCs. The carbonic anhydrase present in the RBC rapidly alters $C{O_2}$ into carbonic acid, which is an unsteady intermediary molecule that instantly detaches into bicarbonate and hydrogen ions. As $C{O_2}$ rapidly converts into the bicarbonate ions, this reaction permits for continual uptake of $C{O_2}$into the bloodstream below its concentration gradient. Around 7% of carbon dioxide is transported in the dissolved state through plasma.

Thus, the correct answer is option ‘A’.

Note: The respiration is the process of breakdown of food(oxidation) to carbon dioxide and water. The carbon dioxide mixes with the blood and is transported to the heart. Through the heart, the blood rich in carbon dioxide is pumped to the lungs and again brought back to heart and is transported to all parts of the body.