Question

When yeast ferments glucose, the products obtained are

• A. ethanol and ${\mathrm{CO}}_2$
• B. methanol and ${\mathrm{CO}}_2$
• C. ethanol and water
• D. water and ${\mathrm{CO}}_2$

Answer 1

The correct option is A ethanol and ${\mathrm{CO}}_2$

Fermentation can be defined as the anaerobic breakdown of carbohydrates and other organic compounds to produce alcohols, organic acids etc. with the help of microorganisms or their enzymes. When oxygen is not available (anaerobic condition) yeast and some other microbes convert pyruvic acid into ethyl alcohol. It is a two step process. In the first step pyruvic acid is decarboxylated to yield acetaldehyde and ${\mathrm{CO}}_2$.
${\mathrm{CH}}_3\mathrm{COCOOH}\stackrel{\mathrm{pyruvic}de\mathrm{carboxylase}}{\to }{\mathrm{CH}}_3\mathrm{CHO}+{\mathrm{CO}}_2$In the second step, acetaldehyde is reduced to ethyl alcohol by NADH (reduced nicotinamide adenine dinucleotide) formed in glycolysis.
${\mathrm{CH}}_3\mathrm{CHO}+\mathrm{NADH}+H^{+}\stackrel{\mathrm{alcohol}\mathrm{dehydrogenase}}{\to }{C}_2{H}_5\mathrm{OH}+{\mathrm{NAD}}^{+}$