What is anaerobic respiration?

• A. Cellular respiration with oxygen.
• B. Conversion of glucose to water and carbon dioxide.
• C. Electron transport chain without ATP production.
• D. Cellular respiration without oxygen, producing less ATP and often lactate or ethanol.

Answer: (D)

Anaerobic respiration happens when oxygen isn’t available. Without oxygen, cells can’t run the full oxidative phosphorylation step, so glycolysis still breaks down glucose to pyruvate and makes a small amount of ATP. To keep glycolysis going, the cell regenerates NAD+ through fermentation. This produces end products like lactate in animals or ethanol and CO2 in yeast. So the description of cellular respiration without oxygen, yielding less ATP and often lactate or ethanol, fits what actually occurs.