Final answer:
Sex pili are the bacterial structures that facilitate the transfer of DNA into or out of a bacterial cell, particularly during the process of bacterial conjugation.
Step-by-step explanation:
The bacterial structures involved in the passage of DNA into or out of the cell are known as sex pili. Sex pili are a type of pilus and are not to be confused with fimbriae, which allow a bacterial cell to attach to surfaces and other cells, or with flagella, which are used by cells to move in aqueous environments. Specifically, the F pilus or sex pilus plays a crucial role in the process of bacterial conjugation, where two bacterial cells physically connect and transfer genetic material.