Final answer:
Cilia are microscopic extensions of the apical cell membrane that move fluids and trapped particles. They have a 9+2 array structure, with nine microtubule doublets surrounding a single microtubule doublet in the center. A basal body attaches the cilium to the cell.
Step-by-step explanation:
Cilia (singular: cilium) 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.
Cilia are composed of a ring of nine microtubule doublets surrounding a single microtubule doublet in the center, forming a structure called a "9 + 2 array." A basal body, which attaches the cilium to the cell, is composed of an array of triplet microtubules embedded in the plasma membrane.