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Flagella vs. Pili: What's the Difference?

Edited by Aimie Carlson || By Harlon Moss || Published on January 29, 2024
Flagella are long, whip-like structures used by cells for movement, while pili are shorter, hair-like structures used primarily for attachment to surfaces or other cells.

Key Differences

Flagella and pili are distinct cellular appendages found in bacteria and some other microorganisms. Flagella are longer, slender, whip-like structures that propel cells through liquid environments. Pili, on the other hand, are shorter and thinner, functioning mainly in adhesion to surfaces and in genetic exchange between bacteria (conjugation).
In terms of structure, flagella are composed of a protein called flagellin and are connected to a rotary motor in the cell membrane, allowing them to rotate and propel the cell. Pili are made of pilin protein and are non-motile, serving as rigid structures that adhere to other cells or surfaces, facilitating processes like biofilm formation.
The primary function of flagella is locomotion. Bacteria use flagella to move towards nutrients or away from harmful substances (chemotaxis). Pili, however, are primarily involved in attachment and colonization, and in some species, in the transfer of genetic material through a process called bacterial conjugation.
The formation of flagella is a complex process involving many genes and proteins, reflecting their role in motility and environmental sensing. Pili formation, while also complex, is more associated with bacterial adhesion and interaction with their environment, including host tissues during infection.
From an evolutionary perspective, flagella and pili have adapted to serve their specific functions efficiently. The mobility provided by flagella is crucial for survival in diverse environments, while pili play a key role in bacterial communities and pathogenicity by enabling adherence and genetic exchange.

Comparison Chart


Cell movement
Cell attachment and genetic exchange


Long, whip-like, composed of flagellin
Shorter, hair-like, composed of pilin


Rotates for propulsion
Non-motile, used for adhesion

Role in Microorganisms

Chemotaxis, environmental sensing
Adhesion, biofilm formation, bacterial conjugation

Formation Process

Complex, involves multiple genes and proteins
Involves specific proteins, crucial for adhesion

Flagella and Pili Definitions


Flagella are tail-like structures that enable bacterial motility.
The bacterium used its flagella to swim towards the nutrient source.


They facilitate bacterial attachment.
The pili played a key role in forming a biofilm on the surface.


They rotate to propel cells through environments.
The flagella's rotation helped the cell navigate through the liquid.


Composed of pilin protein.
The pili’s structure was determined by its pilin protein composition.


Flagella are involved in chemotaxis.
The cell's flagella moved it away from the toxic substance.


Pili are involved in genetic exchange during conjugation.
Bacterial conjugation was facilitated by the transfer of DNA through pili.


Flagella are connected to a rotary motor.
The bacterial flagella's rotary motor allowed for efficient movement.


Pili are small, hair-like structures on bacterial surfaces.
The bacteria used pili to adhere to the host's cells.


Composed of flagellin protein.
The flagella’s structure was analyzed to understand its flagellin composition.


Pili help in colonization and biofilm formation.
The bacteria formed a robust biofilm thanks to its pili.


Plural of flagellum.


Plural of pilus.


Plural of flagellum


A tropical tree, Canarium ovatum, native to maritime Southeast Asia, New Guinea and northern Australia, and cultivated in the Philippines for its nuts.


The edible nut of the tree.


What are flagella made of?

A protein called flagellin.

Do all bacteria have pili?

Many, but not all, have pili.

What are flagella?

Long, whip-like structures for bacterial movement.

How do flagella function?

They rotate to propel bacteria through liquids.

What are pili?

Short, hair-like structures for attachment and genetic exchange.

What is the main function of pili?

To adhere to surfaces and facilitate genetic transfer.

What is chemotaxis in flagella?

Movement towards or away from chemical stimuli.

How do pili help in bacterial conjugation?

They form a bridge for DNA transfer.

Are flagella visible under a microscope?

Yes, with proper staining and magnification.

Do flagella help in bacterial attachment?

Their primary role is in movement, not attachment.

How many flagella can a bacterium have?

It varies, from one to several.

How are flagella different from cilia?

Flagella are longer and fewer in number than cilia.

What are pili made of?

A protein called pilin.

Can pili be seen under a microscope?

Yes, but they are smaller and harder to see than flagella.

Can flagella be found on all bacteria?

No, only on some bacteria.

Can the presence of pili affect antibiotic resistance?

Yes, they can play a role in resistance mechanisms.

What role do pili play in biofilms?

They help bacteria adhere and form biofilms.

Do pili vary in number on bacterial cells?

Yes, the number of pili can vary.

Can flagella be used for diagnosis?

Yes, they can be indicators of certain bacterial species.

Are pili important in bacterial infections?

Yes, especially in adhesion to host tissues.
About Author
Written by
Harlon Moss
Harlon is a seasoned quality moderator and accomplished content writer for Difference Wiki. An alumnus of the prestigious University of California, he earned his degree in Computer Science. Leveraging his academic background, Harlon brings a meticulous and informed perspective to his work, ensuring content accuracy and excellence.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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