What is the movement of water across a selectively permeable membrane from an area of higher concentration to an area of lower concentration called?

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

Answer: (C)

Osmosis is the movement of water across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration (equivalently, toward higher solute concentration on the other side). The membrane allows water to pass but restricts many solutes, so water shifts to balance solute levels across the membrane. This distinguishes osmosis from diffusion, which refers to solute particles moving down their gradient and isn’t limited to water crossing a membrane; active transport requires energy to move substances against their gradient, and filtration is water movement driven by pressure rather than an osmotic gradient.