Final answer:
Fimbriae and pili are protein appendages found on bacterial cells. Fimbriae are short bristle-like proteins that enable attachment to surfaces, while pili are longer protein appendages that aid in surface attachment and DNA transfer between cells.
Step-by-step explanation:
Fimbriae and pili are structurally similar and are often used interchangeably. Fimbriae refer to short bristle-like proteins that enable a cell to attach to surfaces and other cells. Pili, on the other hand, are longer and less numerous protein appendages that aid in surface attachment and can transfer DNA between bacterial cells. Both fimbriae and pili play important roles in bacterial colonization, infectivity, and biofilm formation.