Why do Mary's muscles still feel sore after intense exercise?

• A. Because her muscles have run out of glucose and cannot contract.
• B. Because oxygen levels in her blood are higher than normal.
• C. Because her muscles are producing excess ATP through aerobic respiration.
• D. Because lactic acid has accumulated in her muscle cells due to anaerobic respiration.

Answer: (D)

Verified step by step guidance

1. Understand the context: During intense exercise, the body may not be able to supply enough oxygen to the muscles for aerobic respiration, leading to anaerobic respiration.
2. Recall the process of anaerobic respiration: In the absence of sufficient oxygen, muscle cells convert glucose into energy through glycolysis, producing pyruvate as a byproduct.
3. Learn what happens to pyruvate: Without oxygen, pyruvate is converted into lactic acid instead of entering the mitochondria for aerobic respiration.
4. Understand the effects of lactic acid: Lactic acid accumulation in muscle cells lowers the pH, causing discomfort and soreness in the muscles after exercise.
5. Connect the explanation to the problem: Mary's muscles feel sore because lactic acid has accumulated due to anaerobic respiration during her intense exercise.