Flagella are long, whip-like structures that extend from the surface of many types of cells, including those of bacteria and some eukaryotic organisms. They are primarily used for movement, allowing cells to swim through liquids by rotating or waving in a coordinated manner. In bacteria, flagella can be found in various arrangements, such as single or multiple at one or both ends of the cell. In eukaryotic cells, such as those of sperm cells in animals, flagella are more complex and consist of a structure called the axoneme, which is made up of microtubules. This arrangement enables a different type of movement, often described as a whip-like motion. Flagella play a crucial role in the life cycles of many organisms, aiding in reproduction and nutrient acquisition.