Many examples of organisms that use cilia and flagella can be given. For example, in the human body, motile cilia in the lungs keep dust and dirt out of the bronchi (your breathing tubes) by moving a layer of sticky mucous along that keeps the area clean. Humans also have nonmotile cilia in their kidneys that bend with the urine flow and send signals to alert the cells that urine is flowing. Human (or any mammalian) sperm cells—the cells with the “long, undulating tails” that allow sperm to swim through the oviduct fluids of the female reproductive tract to reach the egg cell—are a classic example of flagella.

In other organisms, flagella and cilia are used for a multitude of processes and movements and for a variety of reasons. For example, several protists such as paramecium also have cilia and produce movement by shifting the cilia through liquid similar to how an oar propels a boat through water. Clams and mussels use cilia for obtaining food as ocean and fresh waters flow by. The ulcer-causing bacteria Helicobacter pylori use multiple flagella to move through mucous in order to reach the stomach’s lining (epithelium).