The number of ATP formed directly by a single Krebs cycle is:
Correct answer: A. One ATP
- A. One ATP
- B. Two ATP
- C. 32 ATP
- D. 36 ATP
Explanation
The Krebs cycle, also known as the citric acid cycle, occurs in the mitochondria and is a critical part of cellular respiration. During each cycle, it directly produces one ATP (or GTP, which is energetically equivalent to ATP). Since the complete oxidation of one glucose molecule requires two turns of the Krebs cycle, two ATP molecules are formed per glucose molecule. The other options refer to the total ATP yield from the entire process of cellular respiration, not just the Krebs cycle. Thus, the correct answer is that a single Krebs cycle directly forms one ATP.
This question appeared on the ETEA MDCAT 2012 paper, which you can sit online with every answer explained.
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About Cellular Respiration
Cellular respiration releases energy from glucose through glycolysis, the link reaction, the Krebs cycle and the electron transport chain, producing ATP. The pathway differs in oxygen availability: aerobic respiration uses oxygen and yields more ATP, while anaerobic respiration produces much less ATP and forms lactic acid in muscles or ethanol and carbon dioxide in yeast.
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