Multiple choice Why do gases diffuse over the respiratory surface? Because pO2 is more in alveoli than in blood. Because pO2 is more in blood than in tissues. Because pCO2 is less in alveoli than in blood. Because pCO2 is less in blood than in tissues. Reveal answer Fill a bubble to check yourself A Correct answer Explanation Gases diffuse over the respiratory surface because pO2 is more in alveoli than in blood.