∞ generated and posted on 2023.05.20 ∞
Movement of substances across lipid bilayers at the expense of energy.
| When you think of 'active' in terms of Active Transport, really what is being referred to is not so much the transport that is active but instead the motivation behind the transport that is active, i.e., it's the difference between driving up a hill (at the expense of energy vs. instead coasting down a hill. |
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 (z>primary active transport) or instead by harnessing existing chemical gradients (or, especially, electrochemical gradients; secondary active transport, a.k.a., cotransport).
Contrast active transport with passive transport and passive diffusion.