Which process describes the movement of water across a semipermeable membrane?

• A. Diffusion
• B. Active transport
• C. Osmosis
• D. Facilitated diffusion

Answer: (C)

The movement of water across a semipermeable membrane is best described by osmosis. Osmosis is a passive transport process where water molecules move from an area of lower solute concentration to an area of higher solute concentration through a semipermeable membrane. This movement occurs to equalize solute concentrations on both sides of the membrane, and it is a critical process in maintaining cell turgor and overall cellular homeostasis.

In terms of passive transport, osmosis specifically refers to water, distinguishing it from other types of diffusion, which may involve solutes. Unlike active transport, which requires energy to move substances against their concentration gradient, osmosis relies on the inherent kinetic energy of water molecules, allowing for the natural flow down their concentration gradient. Facilitated diffusion also does not require energy, but it typically involves the movement of larger or polar molecules across a membrane via specific transport proteins, which is not the case for the simple passage of water through a semipermeable membrane.