Which of the following energy sources requires 2–3 minutes before it begins producing ATP during cellular respiration?

• A. Aerobic metabolism of fatty acids
• B. Phosphocreatine (PCr) system
• C. Direct ATP stores in the cytoplasm
• D. Anaerobic glycolysis

Answer: (A)

Verified step by step guidance

1. Understand the context of the question: The problem is asking about the time it takes for different energy systems to begin producing ATP during cellular respiration. Cellular respiration involves multiple pathways that provide energy to cells, each with varying speeds and durations of ATP production.
2. Review the energy systems mentioned: (1) Aerobic metabolism of fatty acids, (2) Phosphocreatine (PCr) system, (3) Direct ATP stores in the cytoplasm, and (4) Anaerobic glycolysis. Each system has a specific role and activation time in energy production.
3. Recall the characteristics of each system: (a) Direct ATP stores in the cytoplasm provide immediate energy but are depleted within seconds. (b) The Phosphocreatine (PCr) system is a rapid backup that regenerates ATP quickly, lasting for about 10–15 seconds. (c) Anaerobic glycolysis produces ATP without oxygen and activates within seconds, lasting for about 1–2 minutes. (d) Aerobic metabolism of fatty acids is slower to activate, requiring 2–3 minutes to begin producing ATP as it depends on oxygen and complex metabolic pathways.
4. Identify the correct energy source based on the activation time: The question specifies an energy source that takes 2–3 minutes to begin producing ATP. From the review, aerobic metabolism of fatty acids matches this description because it requires oxygen and involves slower, sustained energy production.
5. Conclude that the correct answer is 'Aerobic metabolism of fatty acids' and understand why the other options are incorrect based on their activation times and roles in cellular respiration.