What mechanism is primarily responsible for the movement of oxygen from the alveoli into the blood?

The movement of oxygen from the alveoli into the blood is primarily facilitated by the process of simple diffusion. This is a passive transport mechanism in which oxygen molecules move from an area of higher concentration, found in the alveoli where inhaled air accumulates, to an area of lower concentration, which is the blood within the pulmonary capillaries.

This concentration gradient drives the diffusion of oxygen across the alveolar and capillary walls, which are very thin, allowing for efficient gas exchange. The oxygen then binds to hemoglobin in red blood cells for transport throughout the body. The key aspect of this process is that it does not require energy, as it relies solely on the natural movement of molecules to balance concentrations.

Other mechanisms listed, such as filtration, osmosis, and active transport, are not the primary processes involved in the movement of oxygen in this context. Filtration refers to the movement of fluids through a selectively permeable membrane, commonly influenced by pressure gradients, while osmosis specifically pertains to the movement of water across a semipermeable membrane. Active transport, on the other hand, requires energy to move substances against their concentration gradient, which does not apply to the passive diffusion of oxygen.