Which term describes the movement of water into a cell through a semipermeable membrane due to a higher external water potential?

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

Answer: (D)

Movement of water across a semipermeable membrane when the outside has higher water potential is osmosis. Water potential is the tendency of water to move; it flows from a region of higher potential to one of lower potential. Because the outside has a higher water potential, water will move into the cell to balance the difference, passing through the membrane that restricts solutes. This is a passive process, requiring no energy. Diffusion describes the spread of solutes, not specifically water across a membrane. Filtration is driven by pressure differences, not by a water potential gradient. Active transport uses energy to move substances against their gradient.