Breathing and Exchange of Gases Question 34
34. Carbon dioxide is transported from tissues to respiratory surface by only
(a) plasma and erythrocytes
(b) plasma
(c) erythrocytes
(d) erythrocytes and leucocytes
Show Answer
Answer : a
Hints & Solution
(a) $CO_2$ from the respiratory tissues to the lungs is transported by the blood in 3 ways: (i) In dissolved state or as a physical solution : Very small amount physically dissolved in plasma ( $7 %$ i.e. $\cong 0.3 ml$ of $CO_2$ by each $100 ml$ of blood) (ii) Bicarbonate ions : $\cong 70 %$ (i.e. $\cong 2.5 ml$ per $100 ml$ of blood) $CO_2$ diffuses in plasma & then into RBCs where it (in the presence of carbonic anhydrase) combines with $H_2 O$ to form carbonic acid which is almost spontaneously dissociated into hydrogen ion & bicarbonate ions. (iii) Carbaminohaemoglobin : $\cong 23 %$ (i.e. $\cong$ $1 ml$ of $CO_2$ per $100 ml$ of blood) combines with haemoglobin forming an unstable compound.
