The chemical action of yeast on sugars is called what?

• A. Glycolysis
• B. Fermentation
• C. Krebs Cycle
• D. Oxidative Phosphorylation

Answer: (B)

Fermentation is the process by which yeast converts sugars into ethanol and carbon dioxide when oxygen is limited. It starts with glycolysis, which splits glucose into pyruvate and yields a small amount of ATP and NADH. In the absence of oxygen, pyruvate is then converted to ethanol and CO2, regenerating NAD+ so glycolysis can continue and provide some ATP. This distinguishes fermentation from glycolysis alone (the initial sugar breakdown) and from the Krebs cycle and oxidative phosphorylation, which are parts of aerobic respiration that require oxygen and produce much more ATP. So the chemical action of yeast on sugars in the common sense is fermentation.