Final answer:
Cilia are microscopic extensions of the apical cell membrane that beat in unison and move fluids and particles. They are found in various parts of the body, including the respiratory system and the brain ventricles.
Step-by-step explanation:
Cilia are microscopic extensions of the apical cell membrane that are supported by microtubules. They beat in unison and move fluids as well as trapped particles.
For example, ciliated epithelium lines the ventricles of the brain where it helps circulate the cerebrospinal fluid. Ciliated epithelium in the respiratory system also beats rhythmically to move mucus or other substances through the airway.