An electrochemical gradient is analogous to the water pressure across a hydroelectric dam. Routes unblocked by the membrane (e.g. membrane transport protein or electrodes) correspond to turbines that convert the water's potential energy to other forms of physical or chemical energy, and the ions that pass through the membrane correspond to water traveling into the lower river. Conversely, energy can be used to pump water up into the lake above the dam, and chemical energy can be used to create electrochemical gradients.