Osmosis is best defined as the movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration until equilibrium is reached.

• A. The movement of water across a semipermeable membrane from an area of lower solute concentration to a higher solute concentration until equilibrium is reached.
• B. The diffusion of solutes through a membrane from high concentration to low concentration until equilibrium is reached.
• C. Active transport of water across a membrane
• D. Filtration due to hydrostatic pressure

Answer: (A)

Osmosis is the movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration until equilibrium is reached. This is a passive process driven by differences in water potential caused by solute levels, so water flows to dilute the side with more dissolved particles and moves until the concentrations balance. It is not the diffusion of solutes themselves, which would involve solutes moving from high to low concentration; it is not active transport, which requires cellular energy to move substances against their gradient; and it is not filtration, which is water movement driven by hydrostatic pressure.