When oxygen goes from air in the lungs into the blood, it does so by?

Oxygen transfer from the air in the lungs into the blood occurs through the process of diffusion. This is a fundamental physiological process where molecules move from an area of higher concentration to an area of lower concentration. In the lungs, oxygen concentration in the alveoli (the tiny air sacs) is higher than in the blood within adjacent capillaries.

As a result, oxygen naturally diffuses across the alveolar membrane and into the bloodstream, where it binds to hemoglobin in red blood cells. This passive transport does not require energy and occurs until the concentrations of oxygen in the alveoli and blood reach equilibrium.

Other processes mentioned, such as active transport, would involve the use of energy to move substances against their concentration gradient, while osmosis specifically refers to the movement of water molecules across a semi-permeable membrane. Catalysts are substances that accelerate chemical reactions but do not relate to the movement of oxygen. Thus, diffusion is the correct mechanism for the exchange of oxygen in this context.