How do diffusion and osmosis differ?

• A. Diffusion is only passive; osmosis uses energy
• B. Diffusion moves any solutes; osmosis specifically moves water through a membrane
• C. Osmosis moves solutes; diffusion moves water
• D. Osmosis requires a transport protein; diffusion does not

Answer: (B)

Both processes rely on diffusion driven by concentration differences and do not require energy. Diffusion is the spreading of particles from high to low concentration and can involve many different substances (solutes), not just one. Osmosis is a special kind of diffusion: it is the movement of water specifically, across a membrane that allows water to pass but restricts most solutes. Because the membrane is permeable to water, water moves to balance water potential on both sides, often through channels called aquaporins. The key distinction is what moves: any solutes in diffusion, but water in osmosis, across a membrane.