What is osmosis and why is it important in physiology?

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Osmosis is the diffusion of water across a selectively permeable membrane from a region of lower solute concentration (higher water potential) to a region of higher solute concentration (lower water potential). It is a passive process, requiring no energy, and water moves to balance solute levels by passing through channels called aquaporins (or through the membrane when possible). This movement helps maintain cell volume and overall fluid balance among body compartments. In physiology, osmosis is essential for controlling intracellular and extracellular water distribution, supporting kidney water reabsorption, and preventing cells from swelling or shrinking in response to changing solute concentrations. The option describes osmosis correctly as a passive diffusion of water toward higher solute concentration; the other statements describe energy-dependent transport, diffusion of solutes, or the opposite direction of water flow.