Which statement best describes osmosis?

Which statement best describes osmosis?

• A. The diffusion of solute particles through a semipermeable membrane.
• B. The active transport of water across membranes.
• C. Movement of water across a selectively permeable membrane from higher to lower water potential.
• D. The diffusion of gases across membranes.

Answer: (C)

Osmosis is water moving across a selectively permeable membrane along a gradient of water potential, from higher water potential to lower water potential. Water potential combines how much free water is available and the pressure across the membrane; water moves toward the side with lower potential (more solute or higher pressure) until equilibrium or constraints stop it. This process is passive, requiring no energy input. Jargon-wise, this means water crosses the membrane more readily than many solutes because the membrane is selectively permeable to water. The other statements describe diffusion of solutes, active transport of water (which needs energy), or diffusion of gases—none of these correctly define osmosis.

Osmosis is water moving across a selectively permeable membrane along a gradient of water potential, from higher water potential to lower water potential. Water potential combines how much free water is available and the pressure across the membrane; water moves toward the side with lower potential (more solute or higher pressure) until equilibrium or constraints stop it. This process is passive, requiring no energy input.

Jargon-wise, this means water crosses the membrane more readily than many solutes because the membrane is selectively permeable to water. The other statements describe diffusion of solutes, active transport of water (which needs energy), or diffusion of gases—none of these correctly define osmosis.