Bioelectrogenesis is the generation of electricity by living organisms, a phenomenon that belongs to the science of electrophysiology. The nerve impulse is a bioelectric event. In biological cells, the Sodium-Potassium Exchanger maintains a voltage imbalance, or cell potential difference, between the inside of the cell and its surroundings (see also ion channel). Also called a pump, the exchanger is said to be "electrogenic", because it removes three sodium ions for every two ions of potassium it allows in. The process consumes metabolic energy in the form of ATP. Plant cells also exhibit light-induced electrogenesis. Certain types of bacteria are able to generate electric currents; these are used in microbial fuel cells and educational kits are available for students and hobbyists.