Which condition causes anaerobic metabolism?

• A. Too little oxygen
• B. Too much oxygen
• C. Adequate oxygen
• D. Low carbon dioxide

Answer: (A)

When cells don’t receive enough oxygen, they can’t run the full aerobic energy system efficiently. In this low-oxygen state, cells switch to anaerobic metabolism, mainly glycolysis, to keep making some ATP. This produces far less ATP than aerobic metabolism—about 2 ATP per glucose—and creates lactic acid as a byproduct, which can lead to acidosis if the supply of oxygen remains insufficient. In emergency scenarios, hypoxia from respiratory failure, severe bleeding/shock, or airway obstruction can trigger this shift. Restoring adequate oxygen delivery allows cells to resume aerobic metabolism, increasing energy production and reducing lactic acid buildup. The other conditions—too much oxygen, adequate oxygen, or low carbon dioxide—do not force the switch to anaerobic metabolism.