Which statement correctly describes osmosis?

• A. Water moves across a semipermeable membrane from high water potential to low water potential.
• B. Water moves across a semipermeable membrane from low water potential to high water potential.
• C. Water moves across a semipermeable membrane only when energy is required.
• D. Water moves with equal probability in all directions regardless of water potential.

Answer: (A)

Osmosis is the movement of water across a semipermeable membrane down its water potential gradient. Water potential reflects how freely water molecules can move: it’s higher where there is more free water (less solute) and lower where solute concentration is higher or where pressure constrains water movement. Because water tends to move toward lower water potential, it flows from regions of high water potential to regions of low water potential through the membrane.

That means the statement describing water moving from high to low water potential is describing the actual direction of osmotic flow. Osmosis is a passive process, requiring no external energy input, and it proceeds along the gradient until equilibrium is reached or balanced by opposing pressures. The other ideas—water moving from low to high water potential, requiring energy, or moving equally in all directions regardless of gradient—do not reflect how osmosis operates.