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Secondary Active Transport

The process of secondary active transport involves the simultaneous binding of two different chemical species to the same membrane carrier. Both substances are then transported across the membrane. The significant difference between primary and secondary active transport is that in the latter process one of the substances is moving down its electrochemical concentration gradient and the other is moving up its electrochemical concentration gradient. Thus the energy stored in the electrochemical concentration gradient of one species is used to actively transport the other up its electrochemical gradient.

The electrochemical concentration gradient of the species acting as the energy source has been established by a primary active transport mechanism. Thus the energy for the secondary active transport process is indirectly derived from ATP. Two types of secondary active transport are observed; a co-transport and a counter-transport.