What is the process by which water moves across a semi-permeable membrane from high to low concentration?

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

Answer: (D)

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 (toward higher solute concentration) to balance solute distribution. The membrane allows water to pass while restricting many solutes, and water typically moves through channels called aquaporins as a passive process driven by differences in water potential. This differs from diffusion, which involves solutes moving down their own concentration gradient; filtration, which is driven by pressure differences rather than solute gradients; and active transport, which requires cellular energy to move substances against their gradient.