What are the functions of cilia?

• A. They form the nucleus.
• B. They anchor the cell to the basement membrane.
• C. They sense environmental pH.
• D. They move material along the apical surface.

Answer: (D)

Cilia are motile, hairlike projections on the apical surface of some epithelial cells. Their primary role is to move material along that surface by coordinated beating. In places like the airways, cilia propel mucus and trapped debris upward toward the throat, helping keep the cavity clear. This movement relies on a microtubule-based axoneme with dynein motors that generate the rhythmic bending waves driving flow.

So the best match is moving material along the apical surface. The other statements don’t fit because forming the nucleus is the job of the nuclear envelope and its contents, not cilia; anchoring the cell to the basement membrane uses adhesion complexes like hemidesmosomes, not cilia; and sensing environmental pH isn’t a standard function attributed to cilia.