Which structure is essential for bacterial motility?

The flagella are the structures that are essential for bacterial motility. Flagella are long, whip-like appendages that rotate to propel the bacterial cell forward through liquid environments. This movement allows bacteria to navigate toward nutrients, away from harmful substances, or towards favorable environments, a behavior known as chemotaxis.

In contrast, other structures mentioned serve different functions. The pilus, for example, is primarily involved in adhesion and facilitating genetic exchange between bacterial cells rather than motility. The capsule plays a role in protecting the bacterial cell and evading the immune response but does not contribute to movement. Lastly, the cell wall provides structural support and shape to the bacterium but does not aid in locomotion. Hence, flagella are uniquely suited for movement, making them essential for bacterial motility.