COMMUNICATION IN THE BIOLOGICAL SCIENCES
Department of Biology

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PLANNING AN ANSWER TO AN EXAM QUESTION

Your roommate decides to try his hand at home-brewing beer. He adds baker's yeast, malt, hops, and sugar into a gallon of water. He then puts this mix into a gallon bucket without a lid. You wait to see if he will cover the bucket, but he leaves the mixture exposed to the air. "You know you'll never get any alcohol or carbonation produced like that," you advise your roommate.

"What do you mean?" He replies. "I've got the right proportions of yeast and sugar. It should start fermenting any time now."

Help your roommate, and explain why he will not get enough fermentation to produce alcohol and carbonation.
 

A possible outline for your answer:

• Yeast are facultatively anaerobic.
  
  
• Bucket left open to air.
  
  
• With O₂, yeast will do electron transport.
  
  
• Alcohol & CO₂ are only produced under anaerobic conditions.

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