Which process does not involve the movement of solutes across a plasma membrane?

Osmosis is the process that specifically refers to the movement of water across a selectively permeable membrane, rather than the movement of solutes. This process occurs due to differences in solute concentration on either side of the membrane. Water moves from an area of lower solute concentration to an area of higher solute concentration in an effort to equalize solute levels.

In contrast, diffusion, active transport, and facilitated diffusion all involve the movement of solutes. Diffusion allows solutes to move freely from areas of high concentration to low concentration. Active transport requires energy to move solutes against their concentration gradient, while facilitated diffusion uses transport proteins to help solutes move down their concentration gradient. Since osmosis is focused solely on water movement and does not pertain to solutes, it stands apart from the other processes listed.