In a cell-biology context, which statement correctly describes how water moves via osmosis across a selectively permeable membrane?

• A. Water moves from a region of higher solute concentration to a region of lower solute concentration.
• B. Water moves from a region of lower solute concentration (higher free water concentration) to a region of higher solute concentration (lower free water concentration).
• C. Water moves only through ion channels and cannot cross membranes via aquaporins.
• D. Water movement by osmosis requires ATP hydrolysis to pump water across the membrane.

Answer: (B)

Verified step by step guidance

1. Understand the concept of osmosis: Osmosis is the passive movement of water molecules across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration.
2. Recognize that solute concentration and free water concentration are inversely related: Higher solute concentration means lower free water concentration, and vice versa.
3. Identify the direction of water movement: Water moves from the region of lower solute concentration (which has higher free water concentration) to the region of higher solute concentration (which has lower free water concentration).
4. Note that water moves through specialized channels called aquaporins, which facilitate water transport without requiring energy input (ATP).
5. Conclude that osmosis is a passive process driven by concentration gradients, not by active transport mechanisms like ATP hydrolysis.