Tendons through which muscles are connected to bones are tightly compacted bundles of which one of the following long fibrous protein ?

Tendons are dense fibrous connective tissues that serve the critical function of connecting muscles to bones, facilitating the transmission of force for movement. Structurally, tendons are primarily composed of collagen, specifically Type I collagen, which accounts for approximately 65% to 80% of their dry weight [1]. These collagen fibers are highly aligned and tightly compacted into bundles to provide high tensile strength and structural integrity [1]. While tendons also contain small amounts of elastin (roughly 1% to 2%) to provide some elasticity, collagen is the predominant long fibrous protein that forms the basic structural framework [3]. Other options like fibrin are involved in blood clotting, and cellulose is a structural carbohydrate found in plant cell walls, not animal connective tissues.

Sources

1. [1] https://www.sciencedirect.com/topics/engineering/tendon-tissue
2. [3] https://pmc.ncbi.nlm.nih.gov/articles/PMC4041869/