Which metabolic waste product accumulates in muscle tissue during excessive exertion?

• A. Lactic acid
• B. Ammonia (\(\mathrm{NH_3}\))
• C. Urea
• D. Carbon dioxide (\(\mathrm{CO_2}\))

Answer: (A)

Verified step by step guidance

1. Understand the context: During excessive exertion, muscle cells may experience a lack of oxygen, leading to anaerobic respiration instead of aerobic respiration.
2. Recall the process of anaerobic respiration: In the absence of sufficient oxygen, glucose is broken down into pyruvate through glycolysis. Pyruvate is then converted into lactic acid to regenerate NAD+, which is needed for glycolysis to continue.
3. Identify the metabolic waste product: Lactic acid accumulates in muscle tissue as a byproduct of anaerobic respiration during intense physical activity.
4. Clarify why other options are incorrect: Ammonia (\(\mathrm{NH_3}\)) and urea are nitrogenous waste products primarily associated with protein metabolism and excreted by the kidneys, not muscle activity. Carbon dioxide (\(\mathrm{CO_2}\)) is a byproduct of aerobic respiration, which requires oxygen.
5. Conclude: The correct answer is lactic acid, as it is specifically produced in muscle tissue during anaerobic respiration under conditions of excessive exertion.