Explain how yeast is employed in the industrial production of ethanol for bio‑fuel, specifying the biochemical pathway involved.
Answer
Ethanol is produced by Saccharomyces cerevisiae through alcoholic fermentation: glucose → pyruvate (glycolysis) → acetaldehyde → ethanol, regenerating NAD⁺.
Step-by-step solution
- State that the microorganism used is the yeast Saccharomyces cerevisiae.
- Mention that yeast first metabolises glucose via glycolysis, yielding two molecules of pyruvate and a net gain of 2 ATP and 2 NADH.
- Explain that under anaerobic conditions pyruvate is decarboxylated to acetaldehyde, releasing CO₂.
- Describe the reduction of acetaldehyde to ethanol by NADH, which regenerates NAD⁺ needed for glycolysis to continue.
- Summarise that the overall reaction is: C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂.
Common mistake: Describing ethanol formation as a product of aerobic respiration instead of anaerobic fermentation.
Concept tested: Alcoholic fermentation by yeast
Published · How this solution was prepared and checked
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