d
(d) : Fimbriae are small bristle­like solid structures arising from bacterial cell surface. There are \(300-­400\) of fimbriae per cell. Their diameter is \(3­-10\ nm\) while length is \(0.5-­1.5\ \mu m\). Fimbriae are involved in attaching bacteria to solid surfaces ( \(e.g.\), rock in water body) or host tissues ( \(e.g.\), urinary tract in Neisseria gonorrhoeae). Some fimbriae cause agglutination of \(RBCs\). They also help in mutual clinging of bacteria.