Concentration Gradients

Definition

Concentration is a measure of the amount of solute in a solvent, typically expressed in units of moles per liter. A 1.0 molar solution (abbreviated 1.0 M) contains 1 mole of a solute in 1 liter of total volume. A concentration gradient exists when a higher concentration of a solute is separated from a lower concentration, by a semipermeable membrane.

Overview

Concentration gradients of solutes are common in living cells and are essential sources of energy for all forms of life. Concentration gradients are generated and maintained across biological membranes by ion pump enzymes that transport ionic solutes such as sodium, potassium, hydrogen ions, and calcium across the membrane. Energy is required to produce a gradient, so the gradient is a form of stored energy. An important example is the sodium and potassium ion gradient across most cell membranes, which produces the resting potential and action potentials of excitable membranes like those of neurons. Hydrogen ion...