Active transport is characterized by the movement of substances and ions against the concentration gradient, that is, it always occurs from places where they are less concentrated to places where they are more concentrated. The sodium-potassium pump is an example of active transport. Sodium concentration is higher in the extracellular environment while potassium is higher in the intracellular environment. Importantly, the energy required for this change comes from the breakdown of the ATP (adenosine triphosphate) molecule into ADP (adenosine diphosphate) and phosphate. That is, energy is derived from the degradation of ATP or another high energy phosphate compound, depending on transport proteins.
