Which statement contrasts diffusion and osmosis?

Which statement contrasts diffusion and osmosis?

• A. Diffusion involves solutes moving from high to low concentration, while osmosis involves water moving from low to high solute concentration.
• B. Diffusion involves water moving across a membrane.
• C. Osmosis involves solutes moving across membranes.
• D. Both diffusion and osmosis require active transport.

Answer: (A)

The key idea is that diffusion and osmosis describe movement of different substances under concentration gradients. Diffusion is the random movement of solute particles from areas of high concentration to areas of low concentration until they equalize. Osmosis, on the other hand, is the movement of water across a selectively permeable membrane toward the side with higher solute concentration (lower water potential). This statement is the best because it correctly contrasts what moves in each process: solutes for diffusion, water for osmosis. In contrast, diffusion is not specifically about water moving across a membrane, so the idea that diffusion involves water across a membrane is inaccurate. Osmosis is the process for water movement, not solutes, so saying osmosis involves solutes is incorrect. And both diffusion and osmosis are passive processes that don't require energy input, so stating that they require active transport is incorrect.

The key idea is that diffusion and osmosis describe movement of different substances under concentration gradients. Diffusion is the random movement of solute particles from areas of high concentration to areas of low concentration until they equalize. Osmosis, on the other hand, is the movement of water across a selectively permeable membrane toward the side with higher solute concentration (lower water potential). This statement is the best because it correctly contrasts what moves in each process: solutes for diffusion, water for osmosis.

In contrast, diffusion is not specifically about water moving across a membrane, so the idea that diffusion involves water across a membrane is inaccurate. Osmosis is the process for water movement, not solutes, so saying osmosis involves solutes is incorrect. And both diffusion and osmosis are passive processes that don't require energy input, so stating that they require active transport is incorrect.