Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892



Biology: The Dynamic Science (Mind...

4th Edition
Peter J. Russell + 2 others
ISBN: 9781305389892
Textbook Problem

In muscle fiber in a completely relaxed state:

a. sarcomeres are regions between two H zones.

b. discs of M line proteins called the A band separate the thickfilaments.

c. I bands are composed of the same thick filaments seen in theA bands.

d. Z lines are adjacent to H zones, which attach thick filaments.

e. dark A bands contain overlapping thick and thin filamentswith a central thin H zone composed only of thick filaments.

Summary Introduction


The skeletal muscle consists of muscle fibers that are cylindrical and run along the entire length of the skeletal muscle. The muscle fibers consist of many fibrils that give a striated appearance to the muscle. The muscle fibers are multinucleated and supply nutrients and oxygen to the muscles tissue.


Justification/explanation for the correct answer:

Option (e) states that the dark A bands consist of overlapping thick and thin filaments and the and the central thin H zone, composed of thick filaments, is also present in the A band. In the resting state, the arrangement of muscle fibers is of this type because in the contact state, the H zone is composed of thick and thin filaments both so this is the correct state of myofibrils in the relaxed state of the muscle. Hence, option (e) is correct.

Explanation for the incorrect answer:

Option (a) states that the region between the two H zones is the sarcomere. This statement is incorrect because sarcomere consists of H zones. Sarcomere is the basic unit of contraction of the myofibril. So, it incorrect.

Option (b) states that thick filaments are separated by the disc of the M line protein called the A band...

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