Q. What are flagella and cilia and how do these structures acquire movement? What are some examples of flagellated and ciliated cells in humans?
Flagella and Cilia are structures found in some prokaryotes as well in some eukaryotic cells. They play protection, nutrition and movement roles for the cell. In eukaryotic cells of protists and animals they originate from centrioles that migrate towards the plasma membrane and differentiate into structures projected outside the cell. Each flagellum or cilium is made of nine peripheral pairs of microtubules and one central pair all covered by membrane in bacteria, flagella are made of a protein named flagellin and there can also be fimbria made of pilin
In the fixation base of each flagellum or cilium in the plasma membrane there are proteins that work as molecular motors providing movement for these structures with energy spending. Due to this energy spending flagellated or ciliated eukaryotic cells have a large number of mitochondria.
In humans ciliated cells can be found, for instance, in the tracheal and bronchial epithelium. In these tissues the cilia have the defensive function of sweeping mucous and foreign substances that go into the airways. Sperm cells are a typical instance of flagellated cells, their flagellum is the propulsion equipment for the movement to the ovule.