Oxygen Diffusion in Lungs

Steps:

• Oxygen moves from alveoli to blood via diffusion, driven by concentration differences.
• In lungs, inhaled air fills alveoli with high oxygen levels.
• Blood in lung capillaries arrives with lower oxygen after body use.
• Higher oxygen in alveoli causes net flow into blood until equilibrium.

Why C is correct:

• Diffusion occurs from high to low concentration, as per Fick's law of diffusion.

Why the others are wrong:

• A: Aerobic respiration happens in body cells, not lungs.
• B: Carbon dioxide diffusion out is a separate process, not why oxygen enters.
• D: Lower alveolar oxygen would prevent oxygen entry into blood.

Final answer: C