What is the primary mechanism of osmosis?

The primary mechanism of osmosis is the diffusion of water across a semipermeable membrane. Osmosis specifically involves the movement of water molecules from an area of lower solute concentration to an area of higher solute concentration in order to balance solute levels on either side of the membrane. This process occurs passively, meaning it does not require energy expenditure, and is driven by the concentration gradient of water relative to solutes.

In biological systems, the semipermeable membrane allows water to pass through while restricting the movement of certain solutes, thereby facilitating the equalization of solute concentrations. Osmosis is critical for maintaining cell turgidity, regulating the internal environment of cells, and influencing fluid balance in organisms. Understanding this process helps clarify various physiological and biological functions, such as nutrient absorption and waste removal in cells.

The other options involve different processes: the movement of solutes pertains to diffusion but is distinct from osmosis; active transport requires energy to move substances against their concentration gradient and is not related to the passive movement of water; endocytosis refers to the process by which cells engulf external substances, which is also not related to the passive diffusion of water.