Difference between Cilia and Flagella

Cilia are the small and slender hair-like structures that are present on the surface of mammalian cells. They could be single or many and are primitive in nature. Cilia help in locomotion, and they are involved in mechanoreception. The organisms that have cilia are referred to as ciliates, and they use the cilia for feeding and movement. 

Cilia Could be of Two Types: Motile and Non-motile

The motile cilia are present in a huge number on the surface of the cells, and they are usually found in the respiratory epithelium in humans.

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On the other hand, the non-motile cilia act as the sensory cellular antenna that coordinates with a number of cellular signaling pathways. They also help in proper urine flow by signaling the kidney cells. Non-motile cilia are the primary cilia and help in permitting the transfer of the important particles from one side of the light-sensitive cells to another.

Structure of Cilia

The cilia are made up of microtubules that are coated in the plasma membrane. Each of the cilia consists of nine pairs of microtubules that form the outside ring while the two others make the central microtubules. This structure is known as the axoneme. The outer ring microtubules are made up of motor proteins called dynein. These allow the cilia to move. 

Function of Cilia

Cilia help in the locomotion and the sensory functions, and it plays a vital role in the cell cycle and the replication and thus in the development of humans and animals. Multiple cilia wave in a rhythmic motion helps in keeping the internal passageways free from any foreign agent and mucus. Also, they act as an antenna that aids in receiving the sensory information for the cells and executes these signals from the surrounding fluids. 

Production Of Cilia

Cilia are produced through a process known as ciliogenesis. During the first step, the basal body is docked to the growing ciliary membrane. After this, transition zones are formed. At the ciliary tips, the building blocks of the ciliary axoneme like tubulins are added. This addition takes place in the presence of some process that depends on intraflagellar transport. Few proteins of the basal body are required in the formation of the cilia and for their stability.

Flagella Overview  

Flagella are microscopic hair-like structures that are involved in the locomotion of the cells. The word ‘flagellum’ itself means ‘whip.’ Flagella are known to have a whip-like appearance, and they help a cell to propel through the liquid around it. There are a few organisms in which flagella act as sensory organs to assist in the change of pH and temperature. They are usually found in bacteria, archaea, and eukaryotes. There are four different types of flagella: monotrichous, lophotrichous, peritrichous, and amphitrichous. Monotrichous is a single flagellum that is present at one end or the other. These have the ability to rotate clockwise and anti-clockwise. The lophotrichous are the several flagellums that are attached at one end or the other. They can rotate clockwise and anti-clockwise. Peritrichous are the several flagellums that are attached all over the organism. They are non-polar, and they can rotate anti-clockwise. Amphitrichous are the single flagellum that is attached to both ends of the organism. They are polar and can rotate clockwise and anti-clockwise.  

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Structure of Flagella

The flagella are a helical-like structure that is composed of flagellin protein. The flagella structure can be divided into three parts, namely hook, basal body, and filament. The basal body is attached to the cell membrane and the cytoplasmic membrane. The hook is a broader area that is present at the base of the filament. It connects the filament to the motor protein in the base, and the hook length is a gram +ve bacteria. The filament is the hair-like structure that arises from the hook. 

Function of Flagella

Flagella helps an organism in movement, and they act as sensory organs to detect the pH and temperature changes. A few eukaryotes also use flagellum to increase reproduction rates. It has been found recently that the flagella are also used as a secretory organelle. 

Classification Of Flagella (Organism-Based)

There are three various kinds of flagella (Organism-Based). Underneath are the names and descriptions of these flagella.

• Bacterial Flagella - This type of flagella is discovered in Salmonella typhi, E. Colli. The structure of the bacterial flagella is like a bacterial filamentous structure. The movement of this flagella is like a screw. The bacteria show movement with the help of these structures. The prokaryotes show rotatory motion. The number of the flagellum in one cell can be one, two or more than two.

• Archaeal Flagella - These flagella have similarities to the bacterial flagella. The main difference between the archaeal flagella and the bacterial flagella is that there is no central channel in archaeal flagella but this channel is present in bacterial flagella.

• Eukaryotic Flagella - The eukaryotic flagella are very complex. They move from one place to another and return to their original position. They repeat this process again and again. For example, the sperm cell moves in the female reproductive organ with the help of this flagellum.

Difference between Cilia and Flagella

Cilia 

• They are present in large numbers.

• They are grouped into the category of protozoans, class Ciliata, in the Ciliated epithelium of the Metazoa and other classes.

• They form Cirri by fusing into some protozoans.

• It has similar structures and functions as that of flagella, but cilium is shorter, and movement is quite different.

• It exhibits radial motion.

• Its presence is found on the outer surface of some larvae like Mollusca, Annelida, and Nemertines, which therefore help it with the locomotion.

• Cilia often cover the entire cell.

• The length of the cilia varies between 5 - 10 micrometres. 

•  The thickness of this cell organelle is between 0.3 - 0.5 micrometres.

• The density of the cilia is a hundred or more than a hundred cilia per cell.

• The beating of the cilia is in coordination which means cilia start beating one after the other.

• Besides locomotion, the other functions of cilia are feeding, circulation, aeration, etc.

• The type of swimming motion of the cilia is like the breaststroke.

Flagella

• They are fewer in number.

• Flagella usually do not fuse.

• They are fairly long.

• These are present in protozoans, choanocyte cells of Metazoa, and in other classes- in plants, in gamete cells, and in algae.

• They are fewer in number.

• It exhibits coiled motion.

• They are usually found at one end of the cell.

• The length of the flagella is around 150 micrometers.

• Flagella are not thick. They are around 0.02 to 0.025 micrometers thin. 

• The density of the flagella is 10 or less than 10 flagella per cell.

• The beating of these cell organelle is not coordinated. The beating of each flagellum is independent of each other.

• The only function of the flagella is locomotion. 

• The type of swimming motion of the flagella is like the oar-like style.