Water moves back and forth across the plasma membrane by the process of ________.

A) osmosis
B) filtration
C) facilitated diffusion
D) active transport
E) endocytosis

Osmosis is the process by which water moves across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration until equilibrium is reached. This movement does not require energy, distinguishing it from processes like active transport.