Yeast activation and temperature for fermentation

Steps:

• Dry yeast must be mixed with water to rehydrate and activate enzymes for metabolism.
• Fermentation (anaerobic respiration) in yeast produces CO2 gas, visible as bubbles or foam, but requires optimal temperature.
• At 4°C, metabolic processes slow dramatically due to reduced enzyme activity.
• At 20°C, hydrated yeast ferments quickly, showing signs within an hour.

Why D is correct:

• Yeast performs anaerobic respiration (glycolysis yielding ethanol and CO2) efficiently when hydrated and at 20°C, where enzymes function optimally per the Arrhenius equation on reaction rates.

Why the others are wrong:

• A: Dry yeast remains inactive without water; cold temperature further inhibits any potential activity.
• B: Dry yeast cannot hydrate or metabolize without water, preventing fermentation regardless of temperature.
• C: Water hydrates yeast, but 4°C slows enzyme kinetics too much for visible signs in one hour.

Final answer: D