What is osmosis?

• A. Movement of water across a permeable membrane from an area with higher water potential to a lower water potential
• B. Movement of solutes from high concentration to low concentration
• C. Active transport of solutes using energy
• D. Water moving from an area of lower water potential to higher water potential

Answer: (A)

Osmosis is the movement of water across a selectively permeable membrane driven by differences in water potential. Water potential tends to be higher in areas with fewer dissolved solutes and lower in areas with more solutes or lower pressure. Water will move from the side with higher water potential to the side with lower water potential in an attempt to equalize those potentials.

The option that describes water moving across a permeable membrane from higher water potential to lower water potential matches this idea. The other ideas describe diffusion of solutes (not water), active transport (which requires energy and moves solutes, not water), and water moving from a lower to a higher water potential (which goes against the natural osmotic gradient).