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* In strongly [[acid]]ic conditions it exists as [[arsenic acid]], H<sub>3</sub>AsO<sub>4</sub>;
* in weakly acidic conditions it exists as '''dihydrogen arsenate''' ion, H<sub>2</sub>AsO<sub>4</sub><sup>−</sup>;
* in weakly basic conditions it exists as '''hydrogen arsenate''' ion HAsO<sub>4</sub><sup>2−</sup>;
* and finally, in strongly basic conditions, it exists as the arsenate ion AsO<sub>4</sub><sup>3−</sup>.
In 2008, bacteria were discovered that employ a version of [[photosynthesis]] with arsenites as [[electron donor]]s, producing arsenates (just like ordinary photosynthesis uses water as electron donor, producing molecular oxygen). The researchers conjectured that historically these photosynthesizing organisms produced the arsenates that allowed the arsenate-reducing bacteria to thrive.<ref>[http://www.rsc.org/chemistryworld/News/2008/August/15080802.asp Arsenic-loving bacteria rewrite photosynthesis rules], Chemistry World, 15 August 2008</ref>
In 2010, a team at [[NASA]]'s [[NASA Astrobiology Institute|Astrobiology Institute]] cultured samples of arsenic-resistant [[GFAJ-1]] bacteria from [[Mono Lake]], using a medium high in arsenate and low in phosphate concentration. The findings suggest that the bacteria may partially incorporate arsenate in place of phosphate in some biomolecules, including DNA<ref>[http://www.sciencemag.org/content/early/2010/12/01/science.1197258.short A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus]. Wolfe-Simon F, Blum JS, Kulp TR, Gordon GW, Hoeft SE, Pett-Rdige J, Stolz JF, Webb SM, Weber PK, Davies PCW, Anbar AD, Oremland RS. ''Science'' Express. 02 December 2010.</ref><ref>[http://www.wired.com/wiredscience/2010/12/nasa-finds-arsenic-life-form/ NASA Finds New Arsenic-Based Life Form in California], ''Wired Science'', Dec 2 2010</ref>