Osmosis

Lore & Background

Some kinds of osmotic flow have been observed since ancient times, e.g., on the construction of Egyptian pyramids. The word 'osmosis' descends from 'endosmose' and 'exosmose', coined by French physician René Joachim Henri Dutrochet from Greek words meaning 'within', 'outer', and 'push'.

Reader's Guide

Osmosis is a fundamental process in both physical chemistry and biology. It describes the movement of a solvent—typically water in biological systems—across a selectively permeable membrane toward a higher concentration of solute. This process is driven by a pressure gradient rather than random molecular diffusion, and it can be opposed by applying external pressure, defined as osmotic pressure. Osmotic pressure is a colligative property, meaning it depends only on the molar concentration of the solute, not its identity. In living organisms, osmosis is essential for maintaining cell hydration, turgor pressure in plants, and the balance of water and solutes across cell membranes. Imbalances can lead to cellular dysfunction or death, as seen when freshwater or saltwater fish are placed in water of maladaptive salinity. The mechanism of osmosis has been debated, with earlier models (diffusion and 'bound water') refuted; current understanding emphasizes thermodynamic and mechanical explanations involving chemical potential and pressure differences.

Did You Know?

• Osmosis can be demonstrated when potato slices are added to a high salt solution, causing the potato to shrink and lose turgor pressure.
• Osmotic pressure is defined as the external pressure required to prevent net movement of solvent across the membrane.
• Water molecules travel through cell membranes via aquaporins through a selective pore flow mechanism.
• The word 'osmosis' descends from Greek words meaning 'push' or 'impulsion'.