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Breathing and Exchange of Gases — BIOLOGY STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceBIOLOGYBreathing and Exchange of Gases5 Marks
Question
What are the major transport mechanisms for $CO_2$? Explain.
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Answer

Plasma and red blood cells transport carbon dioxide. This is because they are readily soluble in water.
  1. Through plasma:
About 7% of $CO_2$ is carried in a dissolved state through plasma. Carbon dioxide combines with water and forms carbonic acid.
$\text{CO}_2+\text{H}_2\text{O}\rightarrow\text{H}_2\text{CO}_3\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{(Carbonic acid)}$
Since the process of forming carbonic acid is slow, only a small amount of carbon dioxide is carried this way.
  1. Through RBCs:
About 20 – 25% of $CO_2$ is transported by the red blood cells as carbaminohaemoglobin. Carbon dioxide binds to the amino groups on the polypeptide chains of haemoglobin and forms a compound known as carbaminohaemoglobin.
  1. Through sodium bicarbonate:
About 70% of carbon dioxide is transported as sodium bicarbonate. As $CO_2$ diffuses into the blood plasma, a large part of it combines with water to form carbonic acid in the presence of the enzyme carbonic anhydrase. Carbonic anhydrase is a zinc enzyme that speeds up the formation of carbonic acid. This carbonic acid dissociates into bicarbonate $\left(\mathrm{HCO}_3^{-}\right)$and hydrogen ions $\left(\mathrm{H}^{+}\right)$

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