Texas Education Agency Practice Test

Osmosis is the movement of water across a membrane from an area of higher water potential to an area of lower water potential. Water potential reflects how likely water is to move, with higher potential meaning more free water and lower potential meaning more solute or pressure that reduces water’s tendency to move. Water will flow through the membrane toward the side with lower water potential to balance the conditions.

This is different from diffusion, which is the general spread of particles from high to low concentration and isn’t limited to water or to crossing a membrane in the same way. Active transport requires energy to move substances against their gradient, while facilitated diffusion uses protein channels to move substances down their concentration gradient without using energy. So the process described—water moving to equalize potential across a membrane—is osmosis.