Water moves across the membrane via aquaporins as part of which general process?

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

Answer: (B)

Water moving through aquaporins is a case of osmosis—the diffusion of water across a selectively permeable membrane driven by a solute concentration gradient. Aquaporins act as channels that let water cross the lipid bilayer quickly, allowing water to balance differences in solute concentration on either side. Osmosis specifically describes water's movement in response to these gradients, from areas of higher water potential (lower solute) to areas of lower water potential (higher solute) until equilibrium is approached. While diffusion is the general idea of molecules moving from high to low concentration, and facilitated diffusion involves proteins helping other solutes cross down their gradient, the scenario with water and aquaporins is described as osmosis because it centers on water crossing a membrane due to a solute imbalance.