Cilia and flagella are hair-like structures that extend from the surface of many cells. They are primarily used for movement. Cilia are short and numerous, often covering the entire surface of a cell, while flagella are longer and usually occur singly or in pairs. Both structures are made of microtubules and are powered by the movement of these filaments. These structures play crucial roles in various organisms. In humans, cilia help move mucus in the respiratory tract, while in sperm cells, flagella enable swimming. Both cilia and flagella are essential for the proper functioning of many cells and organisms.