Question

ATP is stored on the myosin cross bridges for immediate energy. After 5 to 6 seconds, this supply is exhausted and the muscle must rely on ________ to quickly produce more ATP.

• A. Phosphocreatine
• B. Lactic acid
• C. Acetyl choline
• D. Pyruvic acid

Answer 1

The correct option is B Lactic acid

• Myofibril activity is required for muscle contraction on the molecular level.
• When ATP binds to myosin, it separates from the actin of the myofibril, which causes a contraction.
  
• The muscle contraction cycle is triggered by calcium ions binding to the protein complex troponin, exposing the active-binding sites on the actin.
  
• ATP then binds to myosin, moving the myosin to its high-energy state, releasing the myosin head from the actin active site.
• When ATP is exhausted lactic acid is produced

So, the correct option is 'lactic acid'.