Both flagella and cilia have a common structural arrangement of microtubules referred to as "9 + 2 array." A single cilium or flagellum is made up of string of nine microtubule doublets that surround a single microtubule doublet in the center.
Flagella are hair-like structures which are usually long and they extend from the plasma membrane. They are used to propel or move an entire cell, for example sperm cell.
Cilia are short hair-like structures that are used to move entire cells. An example is paramecia. Cilia can also be found lining the outer surface of cells such as those of the respiratory tract where they move trapped particles up toward the nose and mouth.
