Concentration gradient

A concentration gradient is a spatial change in a substance’s concentration. It can drive net movement from regions of higher concentration to regions of lower concentration.

Diffusion: The net movement of particles from regions of higher concentration to regions of lower concentration through random motion. Random molecular motion produces net transport down a concentration gradient.
Concentration: The amount of a substance present in a specified volume or amount of mixture. A gradient is a spatial variation in this quantity.
Proton gradient: A difference in proton concentration and electrical potential across a membrane. Cells use this specific gradient to store energy across membranes.
Pressure gradient: A spatial change in pressure that can drive fluid flow from higher-pressure to lower-pressure regions. It drives bulk fluid flow, unlike a concentration gradient's direct effect on particle transport.
Fick's laws of diffusion: Equations describing how diffusion flux depends on concentration differences and spatial distance. They quantify how a concentration gradient sets diffusive flux.
Concentration profile: A description or graph of how concentration varies with position in a system. It represents the spatial pattern whose slope defines a gradient.
Chemiosmosis: The use of ion movement down an electrochemical gradient to drive cellular work, especially ATP synthesis. It converts a membrane gradient into energy for ATP production.
Temperature gradient: A spatial change in temperature that drives heat transfer between regions. It drives heat flow rather than directly expressing a difference in substance abundance.
Chemical potential: A thermodynamic measure of how a system's free energy changes when particles are added. A concentration gradient contributes to differences in chemical potential that drive transport.
Concentration unit: A unit expressing the amount of a substance relative to a volume or amount of mixture. Consistent units are needed to state and compare concentration gradients.

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