Class 11 NEET Biology Breathing and Exchange of Gases

(d) : Diffusion is the net flow of a substance from a region of higher concentration to a region of lower concentration. The exchange of gases between the alveoli and blood in the lung is the result of difference in partial pressure of respiratory gases. The partial pressure of oxygen (pO2) of the alveolar air is higher than the pO2 of blood in alveolar capillaries, thus O2 diffuses rapidly from the alveolar air into the blood of alveolar capillaries. The pCO2 of blood reaching the alveolar capillaries is higher than the pCO2 of alveolar air. Therefore, CO2 into the alveolar air.