Which process moves water across a membrane from high water potential to low water potential?

• A. Osmosis
• B. Diffusion
• C. Active transport
• D. Facilitated diffusion

Answer: (A)

Osmosis is the movement of water across a selectively permeable membrane from a region of higher water potential to a region of lower water potential. Water potential is higher when there is more free water and lower when solutes reduce that free water. The membrane allows water to pass but may block solutes, so water moves to balance potential on both sides. This is a specific case of diffusion focused on water; other processes involve solutes moving (diffusion), using energy to move against gradients (active transport), or moving substances down their gradient with help from proteins (facilitated diffusion), none of which describe water crossing a membrane due to water potential differences.