In section 3.1 of this lesson we mentioned the sodium-potassium pump. Find out what this pump does for a cell, and explain it here. (3.1) Active transport requires the cell to expend energy to transport materials. For example, some channels only work in one direction, either going into or out of the cell, but work regardless of what the concentrations of the material is outside or inside the cell. This allows the cell to maintain different levels of chemicals inside and outside the cell, which can be important for certain chemical processes. (The sodium-potassium pump and proton pump are two examples of this.)