What are flagella also commonly known as?

Flagella are commonly known as cilia in a broader sense when discussing motile structures. However, it's essential to understand that flagella and cilia have distinct differences. Both are hair-like structures that extend from the surface of a cell; they aid in movement and are composed of microtubules.

Flagella are typically longer and usually occur singly or in pairs, while cilia are shorter and more numerous on a cell's surface. Each of these structures plays a critical role in the locomotion of microorganisms and the movement of fluids across cell surfaces in multicellular organisms.

The other options, such as microvilli, fimbriae, and villi, refer to different anatomical structures or functions. Microvilli enhance surface area for absorption, fimbriae are involved in attachment to surfaces or other cells, and villi are found in the intestines and serve to increase surface area for absorption. Therefore, recognizing the context and function of each term is essential for understanding the correct identification of flagella.