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Which statement is correct for muscle contraction : -
More than one option is correct.
A
Length of H-zone decreases
B
Length of A-band remains constant
C
Length of I-band increases
D
Length of two Z-lines increases
Detailed Solution
According to the sliding filament theory, during contraction the thin (actin) filaments slide over the thick (myosin) filaments towards the centre of the sarcomere. The filaments themselves do not shorten.
The A-band equals the length of the thick filaments, so it remains constant.
The H-zone (part of the A-band without overlap) decreases, and may disappear.
The I-band decreases, and the Z-lines come closer, so the sarcomere shortens.
So both 'the length of the H-zone decreases' and 'the length of the A-band remains constant' are correct.
Note: the answer key of the source accepts both of these statements, so both are marked correct here.
The A-band equals the length of the thick filaments, so it remains constant.
The H-zone (part of the A-band without overlap) decreases, and may disappear.
The I-band decreases, and the Z-lines come closer, so the sarcomere shortens.
So both 'the length of the H-zone decreases' and 'the length of the A-band remains constant' are correct.
Note: the answer key of the source accepts both of these statements, so both are marked correct here.