Cilia vs Flagella- Definition and 19 Major Differences


Cilia and flagella are hair-like structures that extend from the surface of some cells and help them to move or to sense their environment. They are found in both prokaryotes (bacteria and archaea) and eukaryotes (protists, animals, plants and fungi). Cilia and flagella have different functions and structures depending on the type of cell they belong to.

Cilia are usually shorter and more numerous than flagella. They can be arranged in rows or clusters on the cell surface. Cilia can beat in a coordinated way to create a wave-like motion that propels the cell or moves fluids over it. For example, cilia on the cells lining the respiratory tract help to clear mucus and dust from the lungs. Cilia can also act as sensory organelles that detect chemical or mechanical signals from the environment. For example, cilia on the cells of the inner ear help to transmit sound vibrations to the brain.

Flagella are usually longer and fewer than cilia. They can be located at one or both ends of the cell or along its sides. Flagella can rotate or whip to create a thrust that pushes or pulls the cell through a fluid medium. For example, flagella on sperm cells help them to swim towards the egg. Flagella can also act as sensory organelles that detect changes in temperature, pH, light or chemical gradients. For example, flagella on some bacteria help them to move towards nutrients or away from toxins.

Cilia and flagella have a similar basic structure in eukaryotes. They consist of a core of microtubules arranged in a "9+2" pattern, surrounded by a membrane and anchored to a basal body. The microtubules are connected by dynein motors that generate the bending movement of the cilia and flagella. The movement is regulated by ATP and calcium ions.

Cilia and flagella have a different structure in prokaryotes. They consist of a single protein filament called flagellin that is attached to a hook and a basal body. The flagellin filament rotates around its axis by the action of a motor protein that is powered by proton flow across the membrane. The direction of rotation can be changed by chemotaxis proteins that sense environmental signals.

Cilia and flagella are important for many biological processes such as locomotion, feeding, reproduction, development, defense and communication. They also have medical relevance as defects in their function or formation can cause diseases such as primary ciliary dyskinesia, Kartagener syndrome, polycystic kidney disease, Chlamydia infection and infertility.

In this article, we will compare and contrast cilia and flagella in terms of their definition, characteristics and key differences.