Exchange Of Gases

Step 1: Concept
Gas exchange occurs via passive diffusion based on partial pressure gradients.
Step 2: Analysis
For Oxygen ( ) to enter the blood, its partial pressure ( ) must be higher in the lungs (alveoli) than in the deoxygenated blood. Conversely, for to leave, its partial pressure ( ) must be higher in the blood than in the alveoli.
Step 3: Conclusion
Diffusion of Oxygen occurs because is higher in the alveoli.
Final Answer:(C)