Active Transport

∞ generated and posted on 2016.08.19 ∞

Movement of substances across lipid bilayers at the expense of energy.

Energy typically is expended because movement up a concentration gradient is in the opposite direction of movement towards equilibrium and perturbing anything away from equilibrium, that is, away from the way it wants to be, always requires an input of energy.

The energy required to move substances against their concentration gradients can be supplied either by ATP (primary active transport) or instead by harnessing existing chemical gradients (or, especially, electrochemical gradients; secondary active transport, a.k.a., cotransport).