Which statement best contrasts diffusion and osmosis?

Which statement best contrasts diffusion and osmosis?

• A. Diffusion is the spontaneous movement of particles down a concentration gradient; osmosis is diffusion of water through a selectively permeable membrane
• B. Diffusion requires energy; osmosis does not
• C. Osmosis is active transport; diffusion is passive
• D. Both describe movement of water only

Answer: (A)

The main idea here is that diffusion is the spontaneous spread of particles from higher to lower concentration, while osmosis is a specific type of diffusion that involves water moving across a selectively permeable membrane. Diffusion applies to any solute, driven by Brownian motion, whereas osmosis specifically describes water moving to balance solute concentrations across a membrane (water moves toward higher solute concentration, lowering water potential on the side with more solute). That distinction is why the statement is the best: it correctly describes diffusion as movement down a concentration gradient and identifies osmosis as the diffusion of water through a selectively permeable membrane. Other choices misstate energy requirements, or mislabel osmosis as active transport, or claim diffusion and osmosis only involve water movement.

The main idea here is that diffusion is the spontaneous spread of particles from higher to lower concentration, while osmosis is a specific type of diffusion that involves water moving across a selectively permeable membrane. Diffusion applies to any solute, driven by Brownian motion, whereas osmosis specifically describes water moving to balance solute concentrations across a membrane (water moves toward higher solute concentration, lowering water potential on the side with more solute).

That distinction is why the statement is the best: it correctly describes diffusion as movement down a concentration gradient and identifies osmosis as the diffusion of water through a selectively permeable membrane. Other choices misstate energy requirements, or mislabel osmosis as active transport, or claim diffusion and osmosis only involve water movement.