The electrochemical gradient could be defined as biologically mediated mass/energy transfer across a system boundary. The electrochemical gradient is a sum of the concentration gradient and membrane potential, which determines the direction of movement of ions through the membrane. It consists of two components: the chemical gradient (concentration gradient), or the difference in the concentration of the dissolved substance at both sides of the membrane, and the electric gradient (membrane potential), or the difference of charges located on opposite sides of the membrane. The gradient arises due to the unequal concentration of ions on opposite sides of the water-permeable membrane. The ions move through the membrane from a region that has a higher concentration to a region with a lower concentration by simple diffusion. Also, the ions carry an electrical charge that forms an electrical potential at the membrane (membrane potential). If there is an uneven distribution of charges on both sides of the membrane, the difference in electric potential generates a force that leads to ion diffusion, until the charges on both sides are balanced.
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