Active Transport is the movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy. Primary active transport directly uses a source of chemical energy (ATP) to move molecules across a membrane against their gradient. Secondary active transport (cotransport), on the other hand, uses an electrochemical gradient, generated by active transport, as an energy source to move molecules against their gradient, and thus does not directly require a chemical source of energy such as ATP.