Answer: I band and H zone decrease; A band stays same; Z discs come closer together.
- A The A band shortens noticeably while the I band stays mostly unchanged throughout contraction
- B I band and H zone decrease; A band stays same; Z discs come closer together
- C All visible bands of the sarcomere shorten by a roughly equal amount during contraction
- D Mainly the H zone changes noticeably, with little movement of the Z discs
Correct answer: B. I band and H zone decrease; A band stays same; Z discs come closer together
Explanation: During contraction: I band (thin filaments only) decreases; H zone (thick filaments only) decreases; A band (thick filaments throughout) stays the SAME length; Z discs move closer together. This is because filaments slide but do not shorten.
A sarcomere (Z line to Z line): during contraction the I band and H zone shorten as thin filaments slide over thick, while the A band stays the same length. Image: SlothMcCarty, CC BY-SA 3.0, via Wikimedia Commons.
Concept context
Types of movement, muscle contraction, skeletal system, joints, and disorders. Important for Class 11 and NEET.