NEET · Biology · STD 11 - 17. Locomotion and movement

During muscle contraction in humans, the

A sarcomere does not shorten
B A band remains same
C \(A, H\) and \(I\) bands shorten
D actin filaments shorten.

Verified Solution

Answer & Solution

Correct Answer

(B) A band remains same

Step-by-step Solution

Detailed explanation

(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.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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