What drives the movement of oxygen from the alveoli into the bloodstream?

Question

Quizplus · Accepted Answer

Oxygen moves from the alveoli to the bloodstream via diffusion down a concentration gradient. The partial pressure of oxygen is higher in the alveoli than in the bloodstream, so oxygen molecules move from an area of high concentration (alveoli) to an area of lower concentration (bloodstream) until equilibrium is reached. This is a passive process and does not require energy or a transporter.

What Drives the Movement of Oxygen from the Alveoli into the Bloodstream