Question

Which of the following occurs during muscle contraction?

• A. Reduction of ATP liberates oxygen
• B. Z lines move closer together
• C. Filaments of myosin slide past filaments of actin.
• D. Muscle fibres lengthen

Answer 1

The correct option is B Z lines move closer together

• 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.
• H zone disappears and Z zone moves towards each other.
• 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.

So, the correct option is 'Z lines move closer together'.