What term describes the movement of water across a semipermeable membrane?

The term that describes the movement of water across a semipermeable membrane is osmosis. This process specifically refers to the passive transport of water molecules from an area of lower solute concentration to an area of higher solute concentration. It is a crucial mechanism in biological systems, as it helps to maintain homeostasis within cells and tissues by regulating fluid balance.

Osmosis occurs because of the selectively permeable nature of cell membranes, allowing water to move while restricting many solute particles. This movement continues until there is an equilibrium in solute concentrations on both sides of the membrane. Understanding osmosis is essential in physiology as it influences various functions, such as nutrient absorption and waste removal in cells.

Other processes mentioned, such as diffusion and active transport, involve different mechanisms and substances. Diffusion generally refers to the movement of solute particles and is not limited to water. Active transport requires energy to move substances against their concentration gradient, which is not the case in osmosis, where water moves passively according to concentration differences. Filtration involves the movement of fluids and solutes through a membrane driven by pressure, not by concentration gradients as seen in osmosis.