Yeast fermentation requires hydration and warm temperature

Steps:

• Dry yeast must be rehydrated in water to activate enzymes for respiration.
• Fermentation proceeds at optimal temperatures around 20°C, where enzymes function efficiently.
• At 4°C, low temperature slows or stops metabolic processes in yeast.
• Evaluate options: only warm, hydrated setup enables visible CO2 production in one hour.

Why D is correct:

• Provides water for hydration and 20°C temperature, enabling yeast enzymes to catalyze anaerobic respiration and produce detectable CO2 gas, per biological requirement for optimal yeast activity.

Why the others are wrong:

• A: 4°C inhibits enzyme activity, preventing fermentation despite hydration.
• B: Lacks water, so dry yeast remains inactive and cannot respire.
• C: 4°C suppresses metabolic rate, halting fermentation even in anaerobic conditions.

Final answer: D