Osmotic

Osmotic refers to processes and properties related to osmosis, the movement of a solvent, typically water, across a semipermeable membrane from a region of lower solute concentration to one of higher solute concentration. The membrane permits solvent passage but largely restricts solutes, so a chemical potential difference drives the flow until the solute concentrations equilibrate on both sides.

Osmotic pressure is the pressure that must be applied to a solution to halt net solvent movement across the membrane. In dilute solutions, it is described by the van't Hoff relation Pi = iCRT, where i is the van't Hoff factor, C is solute molarity, R is the gas constant, and T is the absolute temperature. Osmolarity (osmoles per liter) and osmolality (osmoles per kilogram) quantify solute concentration and predict osmosis and tonicity—whether a solution is isotonic, hypotonic, or hypertonic relative to a reference cell.

Biological systems depend on osmosis to regulate cell volume and fluid balance. Plant cells use osmotic pressure to achieve turgor; animal cells may swell or shrink depending on extracellular tonicity, with potential hemolysis in hypotonic conditions. The kidneys rely on osmotic gradients for water reabsorption, and many medical and laboratory procedures, such as dialysis, use osmotic principles. Osmosis also informs food processing, including osmotic dehydration and preservation techniques.

Osmosis is distinct from simple diffusion of solutes; it specifically describes solvent movement across a semipermeable barrier in response to solute differences.