What are flagella and their functions

Flagella are long structures that function as locomotion organs in many organisms, especially bacteria. Flagella allow organisms to move actively through water or fluids.

What’s that

Flagella are a structure that can be found in various organisms, including bacteria, algae, protozoa, and sperm in animals. Flagella are long feather-like structures that are used for active movement of the organisms that contain them.


The flagella structure consists of three main parts: filament, hook, and basal body. The filament is the most visible and long part, made of a protein called flagellin. The hook is the connection between the filament and the basal body, while the basal body is a structure that is integrated with the cell membrane and is responsible for moving the flagella.

Usually, flagella consist of proteins arranged in a certain pattern, so they are similar to a tail that can move with a rotating or circular motion. Flagella movement is triggered by energy changes in the organism’s body, such as the flow of ions along the flagella tail or changes in the concentration of certain chemicals.

Bacterial flagella:

Flagella in bacteria can rotate like helicopter blades to produce forward or backward movement. This movement is controlled by motor structures located in the basal body. This flagellar motor is similar to an electric motor and produces the power used to rotate the flagella.

Flagella in bacteria have a variety of functions, including helping bacteria move towards sources of nutrition, avoid dangerous substances or extreme temperatures, and interact with other organisms. Flagella are also used by some organisms such as spermatozoa to move towards the egg cell.


The function of flagella varies according to the organism that has them. In bacteria, flagella play a role in helping bacteria move towards or away from a stimulus such as light or a source of nutrition. In protozoa, flagella function as the main means of movement to move places or find food.

In animal sperm, flagella also play an important role in their active movement towards the egg cell. Flagella are able to propulsion sperm following a chemical gradient released by the egg to achieve the goal of fertilization.

In general, flagella are important structures in allowing organisms to move for various purposes, such as obtaining nutrition, avoiding danger, or reproducing.

In some cases, some organisms have multiple flagella that work together to produce more powerful and efficient movements. For example, Escherichia coli has several flagella located in different parts of its body.

So, in general, flagella are structures used by organisms to move actively through water or liquids.

FAQs about Flagella

What are flagella?

Flagella (singular: flagellum) are whip-like appendages found on the surface of certain cells. They are slender, long structures that protrude from the cell and are involved in cell movement. Flagella can be found in various organisms, including bacteria, archaea, and eukaryotes.

What is the structure of flagella?

The structure of flagella can vary depending on the organism. In bacteria and archaea, flagella are composed of a protein called flagellin, which forms a helical filament. The filament is attached to a basal body embedded in the cell membrane. In eukaryotic cells, such as those of animals and protists, flagella have a 9+2 arrangement of microtubules covered by a plasma membrane.

How do flagella function?

Flagella function by propelling cells through a whipping or rotating motion. The movement is achieved through the coordinated bending or rotation of the flagellum. In bacteria and archaea, the rotation of the flagellum is powered by a motor complex located at the base of the flagellum. In eukaryotes, the bending of microtubules by motor proteins generates the movement.

What is the role of flagella in bacteria and archaea?

In bacteria and archaea, flagella play a crucial role in cell motility. They allow these microorganisms to move towards favorable conditions or away from unfavorable ones. Flagella enable bacteria and archaea to swim through liquid environments, such as water or mucus, and navigate their surroundings.

Do all cells have flagella?

No, not all cells have flagella. Flagella are not present in all types of cells. They are primarily found in certain types of bacteria, archaea, and eukaryotic cells. In eukaryotes, flagella are present in organisms such as protists, some algae, and sperm cells of animals.

Can flagella serve other functions besides cell movement?

Yes, flagella can serve additional functions besides cell movement. In some bacteria, flagella can act as sensory organelles, allowing cells to detect and respond to changes in their environment. Flagella can sense chemical gradients, temperature, light, and other external cues, helping cells navigate toward nutrients or away from harmful substances.

Are flagella the same as cilia?

Flagella and cilia are structurally and functionally similar but differ in size and abundance. Flagella are longer and usually occur singly or in pairs, while cilia are shorter and often present in large numbers on the cell surface. Both flagella and cilia facilitate cell movement, but cilia are typically involved in moving fluid or particles along the cell surface, such as in the respiratory tract or reproductive system.

Can flagella be found in human cells?

Flagella are not typically found in human cells. However, human sperm cells are an exception. Sperm cells possess a flagellum, which propels them towards the egg during fertilization. This flagellum enables sperm cells to swim through the female reproductive tract in their journey to fertilize an egg.

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