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In biology, anaerobic respiration is a way for an organism to produce usable energy without the involvement of oxygen; it is respiration without oxygen.^[1] Respiration is a redox reaction that processes energy in a form usable by an organism, chiefly the process of producing ATP,^[2] the "universal energy currency of life".^[3] It employs an electron transport chain, with inorganic molecules other than oxygen used as a final electron acceptor. Anaerobic respiration should therefore not be confused with fermentation, as in ethanol fermentation and lactic acid fermentation.

Etymology

The term anaerobic comes from the Greek: "aer" means air and "bios" means life, while the prefix "an-" means without.

Examples of anaerobic respiration

glucose + 3NO₃^- + 3H₂O 6HCO₃^- + 3NH₄⁺, ΔG⁰' = -1796 kJ

glucose + 3SO₄^2- + 3H⁺ 6HCO₃^- + 3SH^-, ΔG⁰' = -453 kJ

glucose + 12S + 12H₂O 6HCO₃^- + 12SH^- + 18H⁺, ΔG⁰' = -333 kJ

These very important terminal electron acceptors (nitrate NO₃^-, sulfate SO₄^2-, elemental sulfur S) have smaller reduction potentials than O₂, meaning that less energy is released per oxidized molecule of primary electron donor in the above reactions) than in aerobic respiration (i.e. it is less energetically efficient).

See also

• Anaerobic digestion
• Mechanical biological treatment

References

Bibliography

Metabolism map Glucuronate metabolism Pentose interconversion Inositol metabolism Cellulose and sucrose metabolism Starch and glycogen metabolism Other sugar metabolism Pentose phosphate pathway Glycolysis and Gluconeogenesis Amino sugars metabolism Small amino acid synthesis Branched amino acid synthesis Purine biosynthesis Histidine metabolism Aromatic amino acid synthesis Pyruvate decarboxylation Fermentation Fatty acid metabolism Urea cycle Aspartate amino acid group synthesis Porphyrins and corrinoids metabolism Citric acid cycle Glutamate amino acid group synthesis Pyrimidine biosynthesis    All pathway labels on this image are links, simply click to access the article. A high resolution labeled version of this image is available here.