___ are found in humans on sperm only and are involved in the motility of these cells.

The structures you are referring to are flagella. Flagella are long, whip-like appendages that are found on sperm cells and are crucial for their motility. In humans, the presence of flagella allows sperm to swim and navigate through the female reproductive system to reach the egg for fertilization.

The movement of the flagellum is powered by microtubules arranged in a specific pattern in a structure known as the axoneme, which is a part of the sperm's tail. This movement is essential for reproductive success, as sperm must travel significant distances to reach the ovum. Overall, the flagellum plays a vital role in male fertility.