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STD 11 - 17. Locomotion and movement — BIOLOGY STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceBIOLOGYSTD 11 - 17. Locomotion and movement1 Mark
MCQ
During muscle contraction in humans, the
  • A
    sarcomere does not shorten
  • ✓
    A band remains same
  • C
    $A, H$ and $I$ bands shorten
  • D
    actin filaments shorten.
✓

Answer

Correct option: B.
A band remains same
b
(b) : According to sliding­filament theory of muscle contraction, the actin and myosin filaments slide past each other with the help of cross­bridge to reduce the length of the sarcomeres. The smallest unit of muscle contraction is a sarcomere (which is delineated by $Z$ ­lines). As a muscle contracts, the $Z$ lines come closer together (shortening sarcomere), the width ofthe $I$ bands decreases, the width of the $H$ zones decreases, but there is no change in the width of the $A$ band. During relaxation, cross­bridges disappear and actin filaments slide back from A­bands, the width of the $I$ bands and $H$ zones increases, but there is still no change in the width of the A band.

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