The contractile unit in the muscle cell is called the
a. z-line
b. myofilament
c. sarcomere
d. myosin

c. Sarcomere

Explanation:

Sarcomere is one of the basic components of striated muscle that allows muscle contraction. That is, it is the contractile unit in the muscle cell.

The sarcomere is made up of a protein complex, the most important of which are actin and myosin. In the presence of Ca2 +, the ends of the myosin bind to nearby actin molecules and fold with great velocity. The actin filament then moves to the center of the sarcomere, triggering the approach of the two Z lines. This causes the sarcomere to shrink and, to a large extent, lead to contraction of the entire muscle.

yes? sounds right, but you didn’t ask a question.

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these macromolecules could either be amino acids, proteins or nucleic acids. they are responsible for the chemical changes and reactions that affects largely the cell and its composition. take for instance the cytoplasm of the cell where these organelles are settled. these simple organelles are composed of macromolecules which ignites and catalyses different functions that enables cells, in macro-perspective in motion and metabolism. in intestines for example, metabolism happens and breaking down parts of a food to simpler compounds that are used and these nutrients delivered throughout the body and again broken down by into smaller components.