Which process involves the movement of water across a semi-permeable membrane?

The process that involves the movement of water across a semi-permeable membrane is osmosis. Osmosis is a specific type of passive transport where water molecules move from an area of lower solute concentration to an area of higher solute concentration through a semi-permeable membrane. This movement continues until there is an equilibrium of solute concentrations on both sides of the membrane.

Osmosis is crucial for maintaining cellular homeostasis, as it allows cells to regulate their internal environment by controlling the amount of water that enters or leaves the cell. This process differs from other types of transport, such as facilitated diffusion and simple diffusion, which involve the movement of solutes rather than water, and from active transport, which requires energy to move substances against their concentration gradient. Thus, understanding osmosis is essential for grasping how cells interact with their surrounding environment in terms of water balance.