Cilia and Flagella: Structure and Functions

The hair-like extended portion of the cell surface bounded by the cell membrane and containing microtubules and responsible for cell motility are known as cilia and flagella. The cilia and flagella are widely distributed in both the animal and plant cells.

Flagella (singular = flagellum) are complex filamentous, long, thread-like structures that extend from the plasma membrane. They are un-branched, mostly composed of the protein flagellin. The cell contains one or a few flagella, which are primarily used for locomotion. They protrude from the body of the cell and perform their functions effectively. Flagella are longer in size, which grows up to 150 um in length. Flagella are found in both prokaryotic and eukaryotic cell and serve the same functions in both types of cells but are structurally different. The majority of bacteria possess flagella that are used for locomotion.

Cilia (singular = cilium) are microscopic, hair-like, slender, and membrane-bound structures that extend from the surface of many eukaryotic cells. They are short in length(5-20 um)  and perform to move entire cells or move substances around cells. Cilia of the fallopian tubes help to move the ovum towards the uterus and cilia of the respiratory tract move particulate matter toward the throat.

Where Found

Cilia are found in:

  • Ciliate protozoans, such as Paramacium
  • Flame cells of flatworms
  • Many larval forms of invertebrates such as bipinnaria larva, tornaria larva, Trochophore larva, Amphilinidea larva, etc.
  • Epithelium of respiratory tract
  • Fallopian tube
  • Renal tubules
  • Fern sperms
  • Cycad sperms
  • Various gametes of slime molds, fungi, and animals.
image of Paramacium

Paramacium Shows Cilia 

Flagella are found in:

  • All flagellate protozoans such as Euglena, Clamydomonas, Phacus, etc.
  • Choanocytes of sponges
  • Gastrodermal cells of Cnidaria
  • Sperms of animals.
  • Sperms of bryophytes and pteridophytes
  • Gametes of many algae, etc.
image of Euglena

Euglena shows Flagellum

Parts of Ciliary Apparatus

The ciliary apparatus is composed of the following parts:

The shaft: It is the slender cylindrical process that projects from the surface of the cell. It lies external to the cell. In cilia, it is short (3-10 µm), but in flagella, it is longer (up to 150 µm). The axis of cilium consists of 2 central microtubules surrounded by nine pairs of microtubules (9+2) pattern), which is embedded in the ciliary matrix. It is covered by the ciliary membrane, which is the extension of the cell membrane. The basic microtubular framework, i.e., the axis of cilia and flagella, is called axoneme.

The basal body  or granule: The basal body or granule is a centriole-like cellular organelle that is arranged in rows beneath the cell membrane. From this, the body of the cilium originates. The basal body is also known as kinestosome.

Basal Plate: It is a plate-like structure which is located between the basal body and the shaft. In this region, the central singlet fibrils develop.

The ciliary rootlets: These are third components consisting of fine fibrils or ciliary rootlets, which arise from the basal body and converge to form conical bundles that end near the nucleus.

image of Structure and parts of a Flagellum

Structure and Parts of a Flagellum

Types of Cilia and Flagella

There are two types of cilia, such as kinocilia and Stericilia. In this case, kinocilia are motile that have the axonema whereas the steriocilia are non-motile and lack the axonema.

Besides these, Flagella are also of two types, such as tinsel flagellum and whiplash flagellum. In this case, the tinsel flagellum contains hairy outgrowths known as mastigonemes. On the other hand, whiplash flagellum does not contain any hair-like outgrowth.

Bacterial Flagella

In the bacterial cell, the following four types of flagella are found:

Monotrichous: This type of flagellum is found in Vibrio cholera.

Amphitrichous. This flagellum is found in Alkaligens faecalis. It originates from both ends of the bacterium body.

Lophotrichous: They originate from one or both sides of the bacterium body, such as Spirillum.

Peritrichous: They originate from all over the bacterial body and numerous in numbers such as Salmonella Typhi.

image of Bacteria based on flagellum

Bacteria showing flagella

Functions of Cilia and Flagella

  • Flagellum acts as the locomotory organs in many algae and other protists.
  • In the aquatic medium, the flagellum of many organisms helps to capture food particles.
  • Flagellum circulates food in the gastro-vascular cavity in coelenterates or spongocoel (choanocytes) in sponges.
  • The cilia lining in the cells of the respiratory tract remove solid or dust particles from it.
  • In many aquatic organisms, cilia can create water current to receive oxygen (O2) and quick remove of CO2.
  • Cilia perform many essential tasks such as they help to the passage of eggs in the oviduct, passage of excretory substances in the kidneys, etc.
  • In many cases, cilia and flagella perform sensory functions such as sensitivity to changes in light, temperature, and contact, etc.

Difference Between Cilia and Flagella

Cillia

Flagella

Cilia are numerous in number.

Flagella are less (usually 1-2) in number.

Cilia may occur throughout the surface of the cell.

Flagella occur at one end of the cell.

The cilia are shorter in length(5-20µ).

The flagella are longer in size(150µ).

he movement of cilia takes place in coordinated rhythm.

Flagella move independently.

Cilia move in a sweeping or pendular stroke.

Flagella exhibit undulatory motion.

In cross section, Nexin arm is present.

In this case, Nexin arm is absent.

It is found in eukaryotic cells.

It is found in both eukaryotic and prokaryotic cell.

For performing the movement, they use kinesin which has an ATPase activity that produces energy.

Flagella perform functions powered by proton-motive force by the plasma membrane.

Cilia help in locomotion, feeding, aeration, etc.

It helps only in locomotion.

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