Which component is responsible for muscular contraction and cleavage furrow formation?

The component responsible for muscular contraction and cleavage furrow formation is actin. Actin is a protein that polymerizes to form microfilaments, which are critical for various cellular processes, including movement and shape changes. During muscular contraction, actin filaments interact with myosin, another protein, enabling muscle contraction through a process called the sliding filament theory.

In terms of cleavage furrow formation, which occurs during cytokinesis (the final stage of cell division), actin filaments assemble at the cell's equatorial plane, driven by myosin activity. This interaction causes the contraction of the actin ring, leading to the physical pinching of the cell membrane and ultimately separating the two daughter cells. Therefore, the role of actin is central in both muscular contraction and the mechanics of cell division.

Other components like microtubules are important for structural support and movement of organelles but are not directly involved in the contraction mechanism or cleavage furrow formation. Myosin is a crucial player in muscle contraction as it interacts with actin; however, it is not the filament responsible for forming the structure that leads to the contraction itself. Filaments alone isn't specific enough to identify the type; actin is the relevant one in this context.