|biochem, physiol a process by which molecules are enabled to pass across a membrane from a region in which they are in a low concentration to one of high concentration; this requires the expenditure of energy in metabolism and is assisted by carrier proteins, commonly referred to as pumps|
active transport n.
The passage of ions or molecules across a cell membrane against an electrochemical or concentration gradient, or against the normal direction of diffusion.
The movement of ions or molecules across a cell membrane in the direction opposite that of diffusion, that is, from an area of lower concentration to one of higher concentration. Active transport requires the assistance of a type of protein called a carrier protein, using energy supplied by ATP.