How is osmosis best defined?

Osmosis is best defined as the passive movement of water across a selectively permeable membrane. This process occurs when there is a difference in solute concentration on either side of the membrane, leading to the movement of water molecules toward the area of higher solute concentration. This balance helps maintain homeostasis within cells and across biological membranes, allowing cells to regulate their internal environment relative to their external surroundings.

The key aspect of osmosis is that it does not require energy; it is a passive process driven by the concentration gradient of water. The membrane’s selective permeability allows only water to pass, while solutes remain trapped, which results in the movement of water to equalize solute concentrations. Understanding osmosis is fundamental in biology, particularly in contexts like cell biology and physiology, where water balance is crucial for cell function.