Which process involves the movement of water across a semipermeable membrane?

Osmosis is the process that specifically involves the movement of water across a semipermeable membrane. This occurs when water molecules move from an area of lower solute concentration to an area of higher solute concentration in order to achieve an equilibrium on both sides of the membrane.

The semipermeable membrane allows water to pass through while restricting the movement of certain solutes, which is a crucial aspect of osmosis. This process plays a vital role in biological systems, such as in maintaining cell turgor in plants and regulating hydration in animal cells.

In contrast, diffusion refers to the movement of solutes from an area of higher concentration to one of lower concentration, which does not specifically pertain to water. Endocytosis describes the process by which cells engulf substances to bring them into the cell, and active transport involves the movement of molecules against their concentration gradient, requiring energy input. These processes do not directly involve the movement of water through a semipermeable membrane.