Secondary Active Transport
Two types of carrier proteins are involved in secondary active transport: co-transporters and exchangers.
Exchangers move two or more molecules in opposite directions.
Co-transporters move two more molecules in the same direction.
Secondary active transport does not use ATP directly but takes
advantage of a previously existing concentration gradient.
The net direction of movement is dependent on the concentration gradient.
Secondary active transport can move materials against the concentration
gradient, however.