And that means no energy must be inputted into that molecule to move it in that direction. So what that means is this will be passive transport, not active transport. And finally, now that we know what concentration gradient is and electro gradient is, we can basically combine these two concepts into a single concept. So we combine this equation with this equation. And so what that gives us is the following equation. And this equation is the equation that we can basically use to quantify and measure how much energy exists between the two sides of the membrane for molecules that have unequal distribution along the two membranes, as well as an unequal charge distribution.