Explanation

In the tissues, where partial pressure of $CO_{2}$ is high due to catabolism, $CO_{2}$ diffuses into blood (RBCs and plasma) and forms $HCO_{3}^{-}$ and $H^{+}$. At the alveolar site, where $\rho CO_{2}$ is low, the reaction proceeds in the opposite direction, leading to the formation of $H_{2}O$ and $CO_{2}$. Thus, $CO_{2}$ gets trapped as bicarbonate at the tissue level and transported to the alveoli and released as $CO_{2}$