Yeast respires anaerobically to convert simple sugar to carbon (IV) oxide and?

Analyze the question: The question asks what yeast produces, along with carbon (IV) oxide, when it respires anaerobically (without oxygen) using simple sugar.

Explain the concept: Anaerobic respiration in yeast is called alcoholic fermentation. Without oxygen, yeast cannot break glucose down completely. It converts glucose into ethanol (alcohol) and carbon (IV) oxide, and releases a small amount of energy.

Show the solution:

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + energy

(glucose → ethanol + carbon (IV) oxide + energy)

Check each option:

• A. Alcohol: Correct. Ethanol is the second product of this reaction.
• B. Acid: Lactic acid is produced in anaerobic respiration in animal muscles, not in yeast.
• C. Oxygen: Oxygen is not produced. Anaerobic respiration happens in its absence.
• D. Water: Water is a product of aerobic respiration (C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy), not of yeast fermentation.

Answer: The correct option is A. alcohol.

Exam tip: Remember the contrast:

• Yeast (anaerobic): alcohol + CO₂ + energy
• Muscles (anaerobic): lactic acid + energy
• Aerobic respiration: CO₂ + water + energy

Yeast = alcohol, which is why it's used in brewing and in baking, where the CO₂ makes dough rise. You've got this!