Final answer:
Osmosis is the process by which water passes into or out of the cell from a region of high concentration to a region of low concentration until equilibrium is reached.
Step-by-step explanation:
Osmosis, the diffusion of water across membranes from lower to higher solute concentrations, is an essential activity. It allows cells to use water to maintain cellular integrity or to adapt to changes in the solute composition in the extracellular environment. Osmosis across cellular membranes relies on the facilitated transport of water by aquaporins. The passive diffusion of water molecules, can be demonstrated with an artificial (e.g., dialysis) membrane. Water will cross such a membrane if solute concentrations are higher on one side of the membrane. Water crosses the membrane "trying" to equalize the solute concentrations on both sides of the membrane. In effect, water movement is from the side of a membrane where the free water molecule concentration is higher (i.e., where the concentration of solute is lower) to the side where the concentration of free water is lower (i.e., where the concentration of solute is higher).