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42640_Ward's World+MGH Fermentation

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1 Fermentation Article by: Cornelis B. Van Niel, Hopkins Marine Station, Pacific Grove, California. AccessScience, McGraw Hill, Nov. 2021. Access to this content is available to Ward's World readers for free from McGraw Hill's AccessScience, an award-winning, digital STEM resource that provides immediate, authoritative answers to students' thirst for scientific knowledge on topics such as climate change, virology, pollution, and more. Ward's World and McGraw Hill have partnered to offer educators a no-obligation, free trial subscription to this product. Request your free trial today and discover how valuable AccessScience can be for you and your students. An enzymatic transformation of or- ganic substrates, especially carbohydrates, generally accompanied by the evolution of a gas. Fermentation is a chemical trans- formation of organic substrates, especially carbohydrates, to alcohol or organic acids, typically involving the production of a gas, such as carbon dioxide (CO2) or hydrogen gas. It is a physiological counterpart of oxidation, permitting certain organisms to live and grow in the absence of air. Fermentation is used in various industrial processes for the manufac- ture of products such as alcohols, acids, and cheese by the action of yeasts, molds, and bacteria. The best-known example is alcoholic fermentation, in which sugar is converted into ethyl alcohol (ethanol) and carbon dioxide (Fig. 1). This conversion, chemically repre- sented by C6H12O6 —> 2C2H5OH + 2CO2, was established by J. L. Gay-Lussac in 1815. + ward ' s science Key Concepts • Fermentation is a chemical breakdown of organic substrates, especially carbohydrates, to ethyl alcohol or organic acids. • Fermentation is performed primarily by yeasts, molds, and bacteria, and is usually accompanied by the production of a gas, such as carbon dioxide or hydrogen gas. • Fermentation occurs in the absence of oxygen, allowing microorganisms to survive anaerobically. • Two well-known examples are alcoholic fermentation and lactic acid fermentation. • Industrially, alcoholic fermentation is used to manufacture alcohols, acids, and certain foods, such as cheese. Fig. 1: Alcoholic fermentation occurs in yeasts. This process converts pyruvate—the end product of glycolysis—into ethyl alcohol (ethanol), yielding two adenosine triphosphate (ATP) molecules and reducing nicotinamide adenine dinucleotide (NAD+ to NADH). (Copyright © McGraw-Hill Education)

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