Water passing from a region of greater concentration to a region of lesser concentration through a selectively permeable membrane is known as

• A. Diffusion
• B. Filtration
• C. Active Transport
• D. Osmosis

Answer: (D)

Osmosis is the movement of water across a selectively permeable membrane from an area of higher water potential (lower solute concentration) to an area of lower water potential (higher solute concentration). The membrane lets water through while restricting many solutes, so water flows to dilute the more concentrated solution until equilibrium is approached. This is different from diffusion, which describes solute movement down a concentration gradient; filtration, which is pressure-driven; and active transport, which uses energy to move substances against their gradient.