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NEETZoologyLocomotion and Movement

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): During muscle contraction, the length of the 'A' band remains unchanged while the 'I' band shortens. Reason (R): During contraction, the thick filaments (myosin) slide inward over the thin filaments (actin) towards the M line. In the light of the above statements, choose the most appropriate answer

Options

  1. ABoth Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A)
  2. BAssertion (A) is true but Reason (R) is false
  3. CAssertion (A) is false but Reason (R) is true
  4. DBoth Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A)

Correct answer

B. Assertion (A) is true but Reason (R) is false

Step-by-step solution

Assertion (A) is true because during muscle contraction, the actin (thin) filaments are pulled inwards towards the centre of the 'A' band. This causes the 'Z' lines to be pulled inwards, leading to the shortening of the 'I' bands, while the 'A' bands retain their original length. Reason (R) is false because according to the sliding filament theory, muscle contraction occurs by the sliding of the thin filaments (actin) over the thick filaments (myosin), not the other way around. The thick filaments remain stationary

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