ELECTROCHEMICAL GRADIENT
Electrochemical gradient of the membrane consists of two gradients - concentration gradient and membrane potential. By concentration gradient the difference between matter concentrations on both sides of the membrane is meant. Membrane potential is the electric-field gradient in the membrane - the inner side of a membrane is usually charged negatively in relation to the outer one. This kind of potential facilitates penetrating of positively charged ion into the cell, but prevents negatively charged ions from penetrating into the cell.