Biology - Breathing and Exchange of Gases Question with Solution | TestHub

Blood entering the pulmonary capillaries is deoxygenated blood returning from the systemic circulation.

The partial pressure of carbon dioxide ($p{\text{CO}}_2$) in this deoxygenated blood is $45\text{ mm Hg}$. After gas exchange in the alveoli, the oxygenated blood leaves with a $p{\text{CO}}_2$ of $40\text{ mm Hg}$. Thus, before oxygenation, the $p{\text{CO}}_2$ in the pulmonary capillaries is $45\text{ mm Hg}$. This makes statement (1) incorrect and statement (2) correct.

Oxyhaemoglobin is a stronger acid than deoxyhaemoglobin. The formation of oxyhaemoglobin releases ${\text{H}}^{+}$ ions, which slightly lowers the pH of the blood, making statement (3) correct.

High $p{\text{CO}}_2$ and low pH in metabolically active tissues decrease the affinity of haemoglobin for oxygen. This phenomenon, known as the Bohr effect, facilitates the dissociation of ${\text{HbO}}_2$ and the release of ${\text{O}}_2$. Thus, statement (4) is correct..

Answer: The ${}_{pp}{\text{CO}}_2$ of blood in pulmonary capillaries is $40$ mm Hg before oxygenation.