Flagella

The flagellum is one of the most crucial entities in most unicellular organisms. Its presence helps such organisms in more than one way. All of these make it vital for us to learn more about its fundamental aspects to become familiar with its functioning. 

With that being said, let’s quickly go through the basics of flagella including – flagella structure and its function in brief.

What is Flagella?

Flagella are whip-like structures which facilitate movement in specific unicellular organisms. They help cells and organisms to move linearly. These filamentous structures are made up of microtubules. They are found in bacteria, archaea and eukaryotes. 

A flagellum is usually 15-20nm in diameter. After staining with a clear stain, it can be seen under a light microscope. Typically, the staining process helps to increase its diameter.

Flagella Structure 

Essentially, a flagellum is helical in structure and is composed of flagellin protein or globular protein. There are three distinct parts of flagellum –

1. Filament

It is located outside the cell and arises from the hook. It has a structure that resembles thin hair. 

2. Hook

It is the broader region situated at the filament’s base. It is relatively longer in Gram +ve bacteria when compared to gram –ve bacteria. Also, it serves as a connector of filament and motor protein that is present in the base. 

3. Basal Body 

This part is attached to the cytoplasmic and cell membrane, consisting of rings which are surrounded by Mot (a pair of proteins).  These following rings are present in this part –

  • L-ring: This ring is present in Gram –ve bacteria and is attached to the lipopolysaccharide. 

  • P-ring: It is fixed to the cell wall’s peptidoglycan layer.

  • M-S ring: It is fixed to the cytoplasmic membrane.

Check out this figure below to gain a more distinct idea of the structure of a bacterial flagellum. 


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DIY: Draw a diagram of bacterial flagella and label its parts accurately.

Types of Flagella

Flagella are of 6 types. These are listed below.

1. Atrichous

There is no flagellum in organisms. Lactobacillus and Pasteurella are well-suited examples. 

2. Monotrichous

It has a single flagellum on end, which is known as a polar flagellum. It can rotate both clockwise and anti-clockwise. Its clockwise movement helps organisms to move forward, whereas its anti-clockwise movement draws organisms back. Vibrio cholera is an example of Monotrichous.

3. Amphitrichous

There is one flagellum at each end, which is known as a polar flagellum. It can rotate both clockwise and anti-clockwise. The movement is the same as that in Monotrichous. 

4. Peritrichous

Several flagella are present overall. Peritrichous rotates anti-clockwise and aids organisms to move towards one direction. These are also characteristic as the organism cannot move towards any direction or may also tumble if a few flagella break. It may begin to rotate clockwise instead. E. coli is an example of Peritrichous.

5. Lophotrichous

Several flagellums at any of the two ends or both ends are also known as polar flagella. It can also rotate in the clockwise and anti-clockwise direction, wherein the former movement propels an organism forward and the latter draws them back. Spirillum is a suitable example of Lophotrichous.

6. Cephalotrichous

Several flagella are present at both ends of organisms. Both movement and method of locomotion is similar to other polar flagella.  Pseudomonas is a suitable example. 

This figure shows the accurate flagella diagram.

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Function of Flagella

In case you are wondering what do flagellum do, these following will absolve your query –

  • Facilitates locomotion in organisms.

  • Helps to detect a change in pH level and temperature. 

  • Assists eukaryotes to boost their reproductive rate.

  • It is vital for identifying specific organisms.

Test Your Knowledge: The primary flagella function is:

 a) Producing Heat

 b) Locomotion

 c) Producing energy. 

Flagella versus Cilia

This figure highlights the fundamental difference between flagella and cilia

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Find out more about the flagella structure and difference between flagella and cilia by joining our free live classes online. You can also access free PDF solutions and get all your doubts cleared effectively.

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FAQ (Frequently Asked Questions)

1. What is the Role of Flagella in a Bacterial Cell?

Ans. Flagellum helps organisms to move and to detect changes in temperature and pH level. It further helps to identify certain organisms quickly. Also, it accelerates the rate of reproduction in eukaryotes.

2. Where is Flagella Found?

Ans. Flagella is located at the back of a unicellular organism or cell body. A flagellum has a tail-like appearance, and it is primarily responsible for locomotion in organisms. 

3. What are the Types of Flagellation? 

Ans. There are 6 types of bacterial flagellation – i. Atrichous ii. Monotrichous iii. Amphitrichous iv. Cephalotrichous v. Lophotrichous vi. Peritrichous. Notably, each of them has a distinct structure that sets them apart.