Which process is the diffusion of water molecules from a region of high concentration to a region of low concentration through a partially permeable membrane?

• A. Osmosis
• B. Diffusion
• C. Ingestion
• D. Excretion

Answer: (A)

This question centers on osmosis, which is the movement of water across a selectively permeable (partially permeable) membrane. Water moves from where its concentration is higher (higher water potential) to where it is lower (lower water potential) because the membrane allows water to pass while restricting many dissolved substances. That selective passage is what makes this diffusion of water specific to osmosis. In contrast, diffusion in general can involve many substances and doesn’t have to occur across a membrane, and ingestion and excretion are unrelated processes. So the described transfer of water through a selectively permeable membrane from high to low water concentration is osmosis.