What is the process by which cells release energy in the absence of oxygen?

What is the process by which cells release energy in the absence of oxygen?

• A. Fermentation
• B. Glycolysis
• C. Cellular respiration
• D. Adaptation

Answer: (A)

When oxygen isn’t available, cells switch to fermentation to keep producing ATP. Glycolysis can still occur in the absence of oxygen and produces a small amount of ATP, but to keep glycolysis going, NAD+ must be regenerated. Fermentation accomplishes this by converting pyruvate into either lactate or ethanol (plus CO2), using NADH and restoring NAD+. With NAD+ replenished, glycolysis can continue and a little more ATP is produced without oxygen. So fermentation is the energy-releasing pathway in anaerobic conditions, whereas cellular respiration requires oxygen and glycolysis is just the initial step in both aerobic and anaerobic pathways.

When oxygen isn’t available, cells switch to fermentation to keep producing ATP. Glycolysis can still occur in the absence of oxygen and produces a small amount of ATP, but to keep glycolysis going, NAD+ must be regenerated. Fermentation accomplishes this by converting pyruvate into either lactate or ethanol (plus CO2), using NADH and restoring NAD+. With NAD+ replenished, glycolysis can continue and a little more ATP is produced without oxygen. So fermentation is the energy-releasing pathway in anaerobic conditions, whereas cellular respiration requires oxygen and glycolysis is just the initial step in both aerobic and anaerobic pathways.