Which structures are used by bacteria to provide movement?

• A. Flagella
• B. Pili
• C. Capsule
• D. Endospores

Answer: (A)

Flagella are the whip-like appendages that bacteria use to move. They rotate like tiny propellers, driven by a motor in the cell envelope powered by the proton gradient, which lets the cell swim through liquids. This active movement lets bacteria move toward nutrients or away from harm, a behavior often called chemotaxis.

Pili are mainly for attachment and for DNA transfer between cells, and while some forms of movement can occur with pili, it’s not the typical propulsion mechanism taught for bacterial motility. The capsule is a protective layer that helps cells resist drying and immune defenses, not movement. Endospores are dormant, highly resistant forms that survive harsh conditions, not motile structures.