Final answer:
The amino acid from the given list that is completely oxidized for energy within the muscle is leucine, as it is a ketogenic amino acid that cannot be converted back into glucose.
Step-by-step explanation:
The student's question asks about which of the given amino acids is completely oxidized for energy within the muscle. Amino acids serve as a source of energy production through the Krebs cycle, particularly in times like fasting or starvation when the body's carbohydrate and fat stores are low. These amino acids can enter metabolic pathways to become intermediates like pyruvate, acetyl CoA, and oxaloacetate, which are then utilized in the Krebs cycle.
While several amino acids can be used for energy in this way, the question specifies which is completely oxidized within the muscle. The answer lies in the amino acid's ability to be converted into intermediates that enter the Krebs cycle. Alanine is an amino acid that can be synthesized from pyruvate in the muscle and later converted to produce glucose through the process of gluconeogenesis. It is glucogenic, meaning it can result in the formation of glucose.
In contrast, leucine is a ketogenic amino acid because it can degrade into compounds that are precursors for ketone body formation and does not contribute to glucose production via gluconeogenesis. The question specifically asks for the one that is completely oxidized within the muscle. Among the options, leucine is the amino acid that fits this description because it is completely oxidized for energy within the muscle, as it cannot be converted back into glucose and is instead used directly in the energy production process.