Osmosis is defined as the net movement of free water from an area of high water concentration to an area of low water concentration.

• A. True
• B. False; it moves solutes instead
• C. It moves water and solutes together
• D. It depends on temperature

Answer: (A)

The main idea here is how osmosis works: it is the movement of water across a selectively permeable membrane from a region with more free water to a region with less free water. Water moves this way because the membrane is permeable to water but not to most solutes, so differences in water potential drive a net flow of water toward the side with higher solute concentration (lower water concentration). That’s why the statement is true—the definition focuses on the movement of water, not solutes. Temperature can affect how fast osmosis happens, but it doesn’t change the basic fact that osmosis is water moving to balance water potential. If solutes moved, or if water and solutes moved together, that would describe something other than osmosis, and the idea would be incorrect.