Final answer:
The F pilus or sex pilus is the structure responsible for transferring genetic material from a donor cell to a recipient cell during bacterial conjugation, a key process in horizontal gene transfer in bacteria.
Step-by-step explanation:
The structure that physically transfers genetic material from a donor cell to a recipient cell in the process called bacterial conjugation is known as the F pilus, or sex pilus. During conjugation, the F pilus of the donor cell attaches to the recipient cell. The pilus then contracts, drawing the cells together so that their membranes merge, creating a cytoplasmic bridge. Through this bridge, genetic material, typically a plasmid, is moved from the donor cell into the recipient cell.
This process allows for horizontal gene transfer in bacteria, which can include the spread of antibiotic resistance genes via R plasmids or the integration of the F plasmid into the bacterial chromosome to create an Hfr cell. This genetic transfer enhances bacterial adaptability and diversity and has significant implications for biotechnology and medicine.