Final answer:
Cilia are short, hair-like projections that extend from cells and have various functions, such as trapping and removing dust and pathogens in the respiratory system and protecting the eyes from irritants. They beat in unison and move fluids as well as trapped particles.
Step-by-step explanation:
Cilia are short, hair-like projections that extend from some cells, such as cells lining the airways. They are microscopic extensions of the apical cell membrane that are supported by microtubules. Cilia beat in unison and move fluids as well as trapped particles. They have various functions, such as trapping and removing dust and pathogens in the respiratory system, circulating cerebrospinal fluid in the brain's ventricles, and protecting the eyes from irritants as eyelash hair.