Osmosis is the movement of water across a selectively permeable membrane. Which option describes it?

• A. The diffusion of water across a membrane.
• B. Gases crossing membranes.
• C. Movement of water across a selectively permeable membrane from higher to lower water potential.
• D. The active transport of solutes.

Answer: (C)

Osmosis is diffusion of water through a selectively permeable membrane down a water potential gradient. Water moves from the side with higher water potential (less solute) to the side with lower water potential (more solute) because the membrane lets water through but restricts solutes. This movement continues to balance water potentials, and it is a passive process. The other descriptions either miss the focus on water potential and direction, involve gases, or describe active transport of solutes, none of which capture osmosis.