What is the function of pili in bacteria?

Pili, also known as fimbriae, are hair-like structures on the surface of many bacteria that serve crucial functions, primarily in attachment and gene transfer. Their primary role is to facilitate the adherence of bacteria to surfaces, including host tissues or other bacterial cells. This ability to attach is vital for colonization and infection in many pathogenic bacteria.

Additionally, certain types of pili, particularly sex pili, are instrumental in horizontal gene transfer through a process called conjugation. This process involves the direct transfer of DNA between bacteria, promoting genetic diversity and the spread of traits such as antibiotic resistance.

The other options do not accurately describe the primary function of pili. For example, while some structures in bacteria can provide protection against phagocytosis, this is not a primary function of pili. Likewise, pili do not play a direct role in energy production or DNA synthesis; these processes are related to other cellular components and mechanisms. Thus, the correct answer highlights the pivotal roles of pili in both attachment to surfaces and facilitating horizontal gene transfer in bacterial populations.