Flagella are long, whip-like structures that extend from the surface of some cells, enabling them to move. They are primarily found in certain types of microorganisms, such as bacteria and protozoa, and can also be present in the sperm cells of animals. Flagella work by rotating or waving, propelling the cell through its environment. The structure of flagella consists of a core called the axoneme, surrounded by a membrane. In bacteria, flagella are made of a protein called flagellin, while in eukaryotic cells, they are composed of microtubules arranged in a specific pattern. This unique design allows for efficient movement in various aquatic environments.