Osmosis is the diffusion of water across a semi-permeable membrane from an area of low solute to high solute concentration.

• A. Water moves from low solute to high solute
• B. Water moves against its concentration gradient
• C. Water moves independent of membrane
• D. Water moves from high solute to low solute

Answer: (A)

Osmosis is the diffusion of water across a selectively permeable membrane driven by differences in water potential. Water moves from the side with fewer dissolved particles (low solute concentration, higher water potential) to the side with more dissolved particles (high solute concentration, lower water potential). The membrane lets water through but blocks most solutes, so water flows toward the higher solute area to dilute it. This is a passive process, not requiring energy, and it proceeds along the water potential gradient.

So the statement that best describes osmosis is that water moves from an area of low solute concentration to an area of high solute concentration across a semi-permeable membrane. The other ideas conflict with either the direction of water movement, the role of the membrane, or the energy requirement.