What is Anaerobic respiration?
[[File:E. coli Bacteria (7316101966).jpg|thumb|E. coli use anaerobic respiration]] '''Anaerobic respiration''' is a form of [[respiration]] which does not use [[oxygen]]. Elements other than [[oxygen]] are used for [[electron transport]]. Common replacements for oxygen are [[nitrate]]s, [[iron]], [[manganese]], [[sulfate]]s, [[sulfur]], [[fumaric acid]] and [[carbon dioxide]]. ''[[Escherichia coli]]'' uses nitrates and fumaric acid for respiration. For the [[electron transport chain]] to work, there must be a final electron acceptor at the end of the chain.<ref>electron acceptor = a chemical entity that accepts electrons transferred to it from another compound. USGS Electron acceptor. [http://toxics.usgs.gov/definitions/electron_acceptor.html] {{Webarchive|url=https://web.archive.org/web/20151113163706/http://toxics.usgs.gov/definitions/electron_acceptor.html|date=2015-11-13}}</ref> This allows electrons to pass through the chain. In aerobic organisms, this final electron acceptor is oxygen. Molecular oxygen is a highly oxidizing agent and so it is an excellent acceptor. In anaerobes, other less-oxidizing substances such as sulphate (SO<sub>4</sub><sup>2−</sup>), nitrate (NO<sub>3</sub><sup>−</sup>), sulphur (S) are used. These terminal electron acceptors have smaller [[reduction potential]]<nowiki/>s than O<sub>2</sub>, so less energy is released per oxidized molecule.<ref>reduction potential = a measure of how easily a chemical species accepts electrons and so is reduced. </ref> Anaerobic respiration is therefore less efficient than aerobic respiration except, of course, when oxygen is scarce or not apparent. If there is no oxygen present, glycolysis is still able to happen. Pyruvic acid is still produced, but instead of proceeding to the [[Krebs cycle]], [[lactic acid]] is formed making small amounts of [[Adenosine triphosphate|ATP]]. An example of this is when exercising: if the body is not able to get enough oxygen to the muscles, they will make lactic acid. This is what makes the muscles sore. I