The plasma membrane encasing cells is selectively permeable, it controls which substances enter and exit the cell through many processes. These processes can be active or passive requiring a “fuel” such as ATP or can occur without any assistance. One means of transporting molecules across the membrane is by using the electrochemical gradients formed by the plasma membrane. An electrochemical gradient is formed when the charge and chemical concentration is different within and out of the cell. This allows the cell membrane to piggy back much needed molecules on ions such as Potassium or Sodium into and out of the cell. Using this gradient is a passive process which means no energy is required but if a molecule wants to move against the gradient energy is required. In this active process, ATP is consumed to move the molecules against the gradient. The electrochemical gradients allow cells to regulate the transport of molecules efficiently and accurately, this is just one of the means of transport a cell membrane uses to maintain normal processes.

References:

https://www.boundless.com/biology/textbooks/boundless-biology-textbook/structure-and-function-of-plasma-membranes-5/active-transport-66/electrochemical-gradient-336-11473/