Which structure aids in adhesion and movement in prokaryotic cells?

The pilus is a crucial structure in prokaryotic cells that serves both adhesion and movement functions. This hair-like appendage extends from the surface of the cell and plays an important role in helping bacteria adhere to surfaces, including host tissues or biofilms. The capability of the pilus to facilitate adhesion is essential for colonization and infection in pathogenic bacteria.

Additionally, pili can also be involved in a mechanism known as twitching motility, which allows some bacteria to move across surfaces. By extending and retracting, the pilus can pull the bacterial cell closer to itself or propel it forward, thereby contributing to its movement.

In contrast, the other structures serve different purposes. The capsule provides a protective layer that helps prevent desiccation and shields against phagocytosis, but does not significantly contribute to movement. The flagella are primarily responsible for propelling the cell through liquid environments; while they assist in movement, they do not play a significant role in adhesion. The cell wall provides structural support and protection but does not directly facilitate adherence or movement in the same way that pili do.