An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process.
A terminal electron acceptor is a compound that receives or accepts an electron during cellular respiration or photosynthesis. All organisms obtain energy by transferring electrons from an electron donor to an electron acceptor. The process starts with the transfer of an electron from an electron donor. During this process (electron transport chain) the electron acceptor is reduced and the electron donor is oxidized. Examples of acceptors include oxygen, nitrate, iron (III), manganese (IV), sulfate, carbon dioxide, or in some microorganisms the chlorinated solvents such as tetrachloroethylene (PCE), trichloroethylene (TCE), dichloroethene (DCE), and vinyl chloride (VC). These reactions are of interest not only because they allow organisms to obtain energy, but also because they are involved in the natural biodegradation of organic contaminants. When clean-up professionals use monitored natural attenuation to clean up contaminated sites, biodegradation is one of the major contributing processes.