What are the thread-like "tails" that help bacteria move through liquids called?

The correct answer is flagella. Flagella are long, whip-like structures that extend from the surface of many types of bacteria and some other microorganisms. They are primarily used for locomotion in liquid environments, allowing the bacteria to move toward nutrients or away from harmful substances. The movement of flagella is often described as a sort of swimming motion, which can vary in speed and direction depending on the needs of the organism.

In contrast, pili are shorter, hair-like structures that bacteria also possess, but they mainly function for attachment to surfaces or other cells rather than for movement. Cilia are similar to flagella but are typically shorter and more numerous and are more common in eukaryotic organisms rather than in bacteria. Fimbriae are also involved in adhesion but serve different roles from flagella, such as helping bacteria adhere to host tissues.

Understanding the function and significance of flagella in bacterial motility is essential in the study of microbiology, infection control, and the development of antibacterial treatments.