diffusion: Quick Facts

Written and fact-checked by

The Information Architects of Encyclopaedia Britannica

Last updated

Sep. 15, 2026

Photos and Videos

Three-panel diagram showing the diffusion of chloride and potassium ions across a semipermeable membrane. Panel A illustrates movement driven by a concentration gradient, panel B shows both concentration gradient and opposing electrostatic force, and panel C depicts equilibrium potential where forces balance and ion flow is stable. Chloride ions are marked in blue, potassium ions in red, with direction arrows indicating ion movement.

Blue ink diffusing diffusing in water kept in three separate flasks.

Diffusion of molecules across cellular membrane

Two U-shaped tubes illustrate water diffusion across a semipermeable membrane. In diagram A, water moves from side 1 to side 2, driven by osmotic pressure and a concentration gradient, with impermeant substances unable to cross the membrane. In diagram B, hydrostatic pressure opposes the movement. Key concepts such as permeability, osmotic pressure, and impermeant membrane are labeled.

How Do Plants Absorb Water and Nutrients?

See All Videos and Images →

Topics

Osmosis equimolar countercurrent diffusion diffusion thermoeffect diffusion equation diffusion coefficient Loschmidt diffusion tube Graham’s law of diffusion thermal diffusion reverse osmosis diffusivity chemical bonding nuclear fission catalysis nuclear fusion deformation and flow friction thermal conductivity viscosity work absorption

Dig Deeper: More Articles That Discuss This Topic