What does exosmose mean?
Exosmose is a noun referring to the movement of a fluid — typically water — outward through a semipermeable membrane, driven by differences in solute concentration on either side. It is the directional counterpart of endosmose, which describes the corresponding inward flow. The term was introduced in the early nineteenth century by French physiologist Henri Dutrochet during his pioneering investigations of osmotic phenomena in plants and animals, and for much of that century it was standard vocabulary in plant and animal physiology. A leaf placed in a strong salt solution, for instance, loses water by exosmose as the surrounding solution draws moisture out through cell walls. Today the word has largely fallen out of everyday scientific use, replaced by the broader term osmosis or by 'exosmosis', but it remains valuable to readers of older physiological texts and to anyone interested in the history of biology, where precise directional terms like this one shaped early understanding of how living membranes regulate the passage of substances.
nounThe flow of a fluid outward through a semipermeable membrane by osmosis; the outward-directed counterpart of endosmose.
- The outward passage of a fluid through a semipermeable membrane, driven by differences in solute concentration.
"Through the cell membrane, exosmose drew water out of the tissue into the surrounding salt solution."
"In a concentrated sugar solution, exosmose steadily drained water from the plant cells, causing them to lose turgor."
"The physiology lecture traced how exosmose and endosmose together maintain the balance of fluids across membranes."
Pronounced /ɪkˈsɒzməsiːz/ or similar, following the pattern of other -ose/-osis plurals; the plural is rare since the word is seldom used today.
"Different tissues showed different rates of exosmoses under the same conditions."
Coined in the 1820s by physiologist René Joachim Henri Dutrochet, 'exosmose' and its twin 'endosmose' gave science its first vocabulary for the traffic of water across living membranes — decades before the word 'osmosis' existed.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of exosmose
Exosmose was coined in the 1820s by the French physiologist René Joachim Henri Dutrochet, who paired it with endosmose to describe the two directions of fluid movement he observed across organic membranes. The word derives from the Greek prefix exo- ('outside') combined with ōsmos ('a thrusting, impulse'), the root that also underlies modern terms such as osmosis and osmotic. From French scientific usage it passed into English-language physiology texts later in the nineteenth century, where it remained current until superseded by exosmosis and related forms.
Related word forms
How exosmose is actually used
A technical term of nineteenth-century plant and animal physiology that survives chiefly in historical scientific literature. In modern usage it has largely been superseded by 'exosmosis' or simply 'outward osmosis', and it is rarely encountered outside specialist contexts.
Easily confused with exosmose
Endosmose is the inward passage of fluid through a membrane toward the more concentrated solution, whereas exosmose is the corresponding outward passage.