Which Structures Carry Out Cell Movement?

Some cells, including euglenas and various bacterial species, use tail-like projections called flagella to move across a surface. Other cells, including paramecia, use numerous hair-like projections called cilia for locomotion.

Cells may have one or several flagella. Sometimes all of the flagella are located on one side of the organism, and other times they are split between two or more sides. Most species that have flagella use a flagellum to pull themselves along, rather than to push across a surface. They tend to move in a corkscrew-like pattern. Flagella are anchored to cells by structures known as axoneme. Since the flagellum is a living part of the cell, it needs nutrients in order to survive. These materials are passed through the axoneme and into the cytosplasm inside the flagellum.

Cilia are tiny projections that generally cover the entire surface of a cell. A single cell may have thousands of cilia. They move in a coordinated back-and-forth rowing motion to propel the cell across a surface. Like flagella, cilia are mostly comprised of proteins. Some species also use their cilia for purposes other than locomotion. For example, the cilia may move in such as way as to push food into an oral groove or to propel offensive particles away from the cell's surface.