Difference Between Cilia and Flagella

Edited By Irshad Anwar | Updated on Nov 08, 2024 09:54 AM IST

Cilia and flagella can be described as complex cellular structures present in living organisms and are involved in the locomotion of the organism and movement of fluids and in sensory functions too. Cilia and flagella are topics of the chapter Cell: The Unit of Life in Biology.

What are Cilia and Flagella?

Cilia and Flagella are slender and are made of microtubules nevertheless, they possess different functions and properties. Ependymal cilia are shorter and present in large numbers; they are involved in mechanisms such as the clearance of mucus in the respiratory system and signal elimination in sensory organs. Compared to them, flagella are longer, though fewer in number. Most of the structures in the cell shapes of the known microorganisms, which are mainly characterised by ciliary and flagellar beats, aid cell propulsion by undergoing rotational or wave-like motions.

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This Story also Contains

What are Cilia and Flagella?
Structure of Cilia and Flagella
Types and Classification
Function and Mechanism of Action
Key Differences Between Cilia and Flagella
Similarities Between Cilia and Flagella
Diseases and Disorders Related to Cilia and Flagella
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Difference Between Cilia and Flagella

Structure of Cilia and Flagella

The structure of cilia and flagella is given below-

Cilia

Structure:

Cilia are slender, tubular extensions from the cell membrane or surface of the cell. They are usually abundant on the cell membrane and have been noted to be essential components of the cell membrane.

Arrangement:

Cilia have a basic structural component called the axoneme which is composed of nine peripheral microtubule doublets and a central pair of microtubules.

Cilia structure

Flagella

Structure:

It is longer, thinner, and fewer than cilia; it has the movement of a whip. These come out of the cell surface and are concerned with cell movement.

Arrangement:

Just as it is in cilia, eukaryotic flagella possess a ‘9+2’ organization of microtubules in which nine outer doublets surround two central microtubules.

Flagella structure

Types and Classification

Cilia can be classified into:-

Cilia

Motile Cilia

Function: Motile cilia are involved in the movement and flow of fluids and therefore have crucial functions like mucus removal in the respiratory system, and movement of the eggs in the fallopian tubes.

Examples: Identified in the respiratory tract’s epithelial cells and the epithelium of the female reproductive system.

Non-motile Cilia

Function: Structural cilia mainly function as tabs that help in perceiving signals in the environment and transmitting them into the cell.

Examples: Located on olfactory neurons located in the nose and photoreceptor cells of the retina.

9+2 arrangement of cilia

Flagella

Given are the structure and function of flagella-

Prokaryotic Flagella

Structure: Flagella found in prokaryotic organisms are small structures made up of flagellin and are mainly involved in movement.

Movement: Rotational movement occurs with bacteria even as they propel themselves through the water as they search for nutrients.

Examples: Usually found in bacteria like E. coli and Salmonella

Eukaryotic Flagella

Structure: The eukaryotic flagella are elaborate structures that are made up of microtubules in the “9+2” formation.

Movement: They come in a sinusoidal pattern so that they help in the propulsion and the movement of the cell.

Examples: Present in sperms for movement, and some of the protozoa for their means of movement.

Eukaryotic and Prokaryotic Flagella

Function and Mechanism of Action

Following describe the function and mechanism of cilia and flagella-

Cilia

Movement and locomotion:

Cilia enable the movement and locomotion of several organisms ranging from single-celled; protists such as Paramecium to complex organisms which include; humans. In the animal Paramecium, the coordinated coordination of cilia is vital for the movement through water, in the respiratory tract the ciliary movement is very important in the removal of mucus and other materials.

Sensory functions:

Cilia are also involved in sensory functions to the environment to receive signals as well as translate these signals to the cell. It is noted that in the human body, primary cilia take part in the transduction of various signals which includes the sensory processes of kidneys and eyes.

Flagella

Locomotion and propelling cells:

While flagella are mostly involved in cell movement and navigation it has to be understood that the primary purpose of flagella is to allow an organism to move within its environment. In bacteria, moving by swimming and orienting in the space is facilitated by the flagella while in sperm cells, it moves the cell towards the egg during reproduction.

Sensory functions:

Like cilia, flagella occasionally have some sort of sensation function to feel changes in the surroundings and affect corresponding behavioural reactions. For instance, the bacterial flagella have chemotactic properties; this means that bacteria can feel chemical differences and can move in the direction of such differences to locate the best conditions.

Key Differences Between Cilia and Flagella

The following summarises the structural and functional differences between cilia and flagella.

Aspect	Cilia	Flagella
Structure	Shorter, numerous, "9+2" arrangement of microtubules	Longer, fewer, "9+2" arrangement of microtubules
	Present in large numbers on the cell surface	Typically fewer in number
	Primarily involved in locomotion and fluid movement	Mostly sensory roles
Function	Facilitate movement, fluid flow, and sensory perception	Enable cell propulsion and sensory functions
	Found in the respiratory tract, reproductive system, and sensory organs	Found in bacteria, sperm cells, and certain protists
Movement Mechanism	Coordinated beating pattern	Wave-like undulation or rotational movement
	Generates fluid movement or propels cells	Propels cells through a fluid medium

Similarities Between Cilia and Flagella

The following summarises the similarities between cilia and flagella.

Aspect	Cilia	Flagella
Shared Structural Components	Both are composed of microtubules and associated proteins	Microtubule-based structures with dynein arms
Common Origin	Evolved from ancestral motility structures	Shared evolutionary pathways
Functional resemblance	Are used to move liquid across the cells.	They also help to move liquids past the cells.

Diseases and Disorders Related to Cilia and Flagella

The diseases and disorders are explained below-

Ciliary Disorders

Primary ciliary dyskinesia: PCD is an inherited disease that is associated with a failure of ciliary motility resulting in repeated respiratory infections, sinus, bronchiectasis, and problems in conception.

Kartagener syndrome: Specifically, it is also called primary ciliary dyskinesia with situs inversus, and is featured by chronic respiratory infections, sinusitis, bronchiectasis, and inversion of the heart and liver.

Flagellar Disorders

Impact on fertility: Mutations in flagella in sperm can be a cause of male infertility due to the problems associated with the motility of sperm found in semen to subsequently fertilize the egg.

Bacterial infections: Flagella are involved in the pathogenesis and virulence of different bacteria, including Salmonella, and Pseudomonas aeruginosa because they facilitate the organisms’ invasion of host tissues and the development of infections.

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