Question

Assertion :Partial pressure of $O_2$ in the alveoli is 104 mm Hg. Reason: Partial pressure of $O_2$ is dependent upon concentration of $C{O}_2$.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
• C. Assertion is correct but Reason is incorrect.
• D. Both Assertion and Reason are incorrect.

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.

• The partial pressure of oxygen in alveolar air is about 104 mm Hg, whereas the partial pressure of the oxygenated pulmonary venous blood is about 100 mm Hg.
• When ventilation is sufficient, oxygen enters the alveoli at a high rate, and the partial pressure of oxygen in the alveoli remains high.
• Blood that is low in oxygen concentration and high in carbon dioxide concentration undergoes gas exchange with air in the lungs.
  
• This concentration gradient allows for gas exchange during respiration. Hence, Partial pressure of O2 in the alveoli is 105 mm Hg and Partial pressure of O2 is dependent upon the concentration of CO2.

So, the correct answer is 'Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion'.