Which mechanism involves the transfer of plasmids via a sex pilus in prokaryotic cells?

The mechanism that involves the transfer of plasmids via a sex pilus in prokaryotic cells is conjugation. This process is a form of horizontal gene transfer where one bacterium transfers genetic material to another through direct contact. The sex pilus, a filamentous structure that extends from the donor bacterium, facilitates this connection by attaching to the recipient bacterium, allowing the transfer of plasmid DNA.

During conjugation, the plasmid can carry various genes, including those that confer antibiotic resistance or other advantageous traits. This method is particularly significant in the spread of antibiotic resistance among bacterial populations, as it allows for rapid sharing of these traits.

In contrast, transduction involves the transfer of genetic material between bacteria via bacteriophages, which are viruses that infect bacteria. Transformation refers to the uptake and incorporation of free DNA from the environment into a bacterial cell. Binary fission, on the other hand, is the process of asexual reproduction in prokaryotes where a single cell divides into two identical daughter cells, and it does not involve the transfer of genetic material between cells. Thus, the unique characteristic of plasmid transfer through a sex pilus in conjugation clearly identifies it as the correct answer.