Which of the following is a correct statement about the energy systems and fuels used by the body during cellular respiration?

• A. Fatty acids are directly converted into ATP during glycolysis.
• B. Oxygen is not required for any stage of cellular respiration.
• C. Glucose is the primary fuel molecule used in glycolysis to produce ATP.
• D. Proteins are the first choice of fuel for cellular respiration under normal conditions.

Answer: (C)

Verified step by step guidance

1. Step 1: Begin by understanding the process of cellular respiration, which is the metabolic pathway that converts biochemical energy from nutrients into ATP, the energy currency of the cell. Cellular respiration primarily involves glycolysis, the citric acid cycle, and oxidative phosphorylation.
2. Step 2: Analyze the role of glucose in glycolysis. Glycolysis is the first stage of cellular respiration and occurs in the cytoplasm. Glucose is the primary fuel molecule used in glycolysis, where it is broken down into pyruvate, producing ATP and NADH.
3. Step 3: Clarify why fatty acids are not directly converted into ATP during glycolysis. Fatty acids undergo beta-oxidation in the mitochondria to produce acetyl-CoA, which enters the citric acid cycle. This process is separate from glycolysis.
4. Step 4: Address the requirement of oxygen in cellular respiration. Oxygen is essential for the electron transport chain during oxidative phosphorylation, where the majority of ATP is produced. However, glycolysis itself does not require oxygen and can occur anaerobically.
5. Step 5: Explain why proteins are not the first choice of fuel under normal conditions. Proteins are typically used for structural and functional roles in the body. They are only broken down into amino acids for energy production during prolonged fasting or starvation, making glucose the preferred fuel molecule under normal conditions.