Cilia and Flagella

Cilia and flagella are two cell organelles primarily found in protozoa, such as amoeba, paramecium, and euglena. However, they are also found in other microorganisms, such as bacteria, algae, and fungi, and in animals, except for higher plants.

They are motile cellular appendages made of microtubules and remain covered by the plasma membrane. Both cilia and flagella aid in movement.

Compare and Contrast Cilia and Flagella

Although cilia and flagella share many characteristics, they are also different in a number of ways.

Difference between Cilia and Flagella

Cilia are short, microscopic, hair-like structures or organelles extending in large numbers from the surface of eukaryotic cells. In contrast, flagella are long, complex filamentous cytoplasmic structures protruding through the cell wall.

Basis	Cilia	Flagella
1. Found	Only in eukaryotes such as areas of the respiratory tract and female reproductive track	Both eukaryotes and prokaryotes
2. Composed Of	Polymers of globular proteins called tubulin, the motor protein called dynein, and nexin	Polymers of tubulin and dynein. Bacterial flagella also contain flagellin
3. Structure and Organization	Length: Short, hair-like, (5-10)µ in length Thickness: Around 0.3 to 0.5 μm in thickness Organization: Possess a central bundle of microtubules called the axoneme 9 outer doublet microtubules surround a central pair of singlet microtubules When viewed under an electron microscope, the cross-section of the axoneme shows the characteristic 9 + 2 arrangement	Length: Long, whip-like, or thread-like organelle. 150µ in length Thickness: Around 0.02 to 0.025 μm in thickness Organization: Eukaryotic flagella are remarkably similar in their organization to cilia, showing the characteristic 9 + 2 arrangement of microtubules Prokaryotic flagella are simpler structures made up of flagellin
4. Functions	Helps primarily in locomotion. It also helps in feeding circulation, aeration, and respiration	Help mainly in locomotion
5. Beating Pattern	Complicated, can move in a wide range of motions	Circular, wave-like, or propeller-like motion
6. Distribution in Cell	Distributed throughout the cell surface	Present at one end or two ends or all over the surface
7. Density	Numerous, approximately hundreds per cell	Fewer than cilia, less than 10 per cell
8. Energy Requirement	Use ‘kinesin,’ having an ATPase activity that produces energy to perform the movement	Powered by the proton-motive force generated in the plasma membrane in prokaryotes. It is ATP-driven in eukaryotes
9. Position In Cell	Present throughout the surface of the cell	Either present at both the ends of the cell or all over the surface
10. Types	Two types: motile or non-motile	Three types: bacterial, archaeal, and eukaryotic

11. Types of Motion	a) Rotational, like a motor b) Very fast-moving	a) Wave-like, sinusoidal undulating movement b) Slow moving
12. Beating Pattern	Beating in a coordinated rhythm either simultaneously (synchronous) or one after the other (metachronous)	Beating is independent of each other
13. Cross section	Nexin arm present	Nexin arm absent

How are Cilia and Flagella Alike

Although they differ in many aspects, cilia and flagella have similarities. They are

Function primarily in locomotion.
Arise from the basal body, a centriole-like structure
Develop from the cell’s plasma membrane
Have an axoneme, a central filament. Axoneme has 11 microtubules, of which 9 are in pairs (doublet), and the remaining 2 are located in the center (singlet)., showing the typical 9+2 arrangement of microtubules

Conclusion

Cilia and flagella are two significant microscopic appendages of cells. Cilia are present in both animals and microorganisms but absent in higher plants. In contrast, flagella are used for mobility in bacteria and gametes (sperm and egg cells) of eukaryotes. Both cilia and flagella serve locomotory functions but in different manners. Both rely on dynein, a motor protein, and microtubules to work.

References
- 1. Flagella and Cilia – Openoregon.pressbooks.pub
  2. What Are the Main Functions of Cilia & Flagella? – Sciencing.com
  3. Cilia and Flagella – Micro.magnet.fsu.edu
  4. Cilia and Flagella: Structure and Movement – Ncbi.nlm.nih.gov