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Question

Select true or false
i. Shortening of sarcomere occurs when Z lines attached to actin filaments are pushed outwards.
ii. During contraction, I bands retain their lengths. 
iii. During contraction, A bands get reduced in length.
 


A
I- True, ii- False, iii-False
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B
I- False, ii- True, iii-True
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C
I- False, ii- False, iii-False
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D
I- True, ii- True, iii-False
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Solution

The correct option is A I- False, ii- False, iii-False
The A band contains thick and thin filaments overlapping with each other. The I band is formed only of thin actin filaments. The H zone is formed only of thick myosin filaments. The region between consecutive Z lines is a single sarcomere.
During muscle contraction, the I band is reduced in size as the overlap between the thick and thin filaments increases. Consequently, the H zone also decreases in length. As the Z lines come closer together, the sarcomere shortens. So, the sarcomere, the I band, and the H zone decrease in length during muscle contraction. However, the A band does not change length during muscle contraction, since its length is the same as the length of the thick filaments.

Biology

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