The structures that help some bacteria to attach to rocks and/or host tissues are

Explanation

Fimbriae are indeed small, bristle-like structures that extend from the surface of bacterial cells and are crucial for adhesion to various surfaces, including rocks and host tissues. They allow bacteria to establish themselves in suitable environments, such as the urinary tract in the case of Neisseria gonorrhoeae. In contrast, mesosomes are involved in other cellular processes but do not primarily function in attachment. Holdfasts are specialized attachment structures, but they are not as ubiquitous as fimbriae across different bacterial species. Rhizoids, while serving a similar anchoring function in other organisms, are not characteristic of bacteria.