Cilia-and-Flagella

Cilia and Flagella: Comparison, Distribution, Structure and Working

Cilia and Flagella

Cilia and Flagella are the microscopic, motile, filamentous projections from the cytoplasm of the cell. They help in locomotion, and sensory functions and perform other mechanical functions of cells. Based on appearance, both cilia and flagella are identical structures but they can be distinguished by the functions they perform, their size, and numbers.

Comparison of Flagella and Cilia

Flagella are less in number and occur at one or two ends of the cell while cilia are many and can occur throughout the surface of the cell. The flagella are longer whereas the cilia are shorter in length. Flagella usually beat independently but cilia tend to beat in a coordinated rhythm. Flagella extends from the plasma membrane. On the other hand, cilia are appendages of the cytoplasm.

The basic difference between cilia and flagella is in the movement. Flagella show undulatory motion while cilia have biphasic movement i.e., the movement consists of two phases the one being effective stroke and the other being recovery stroke (generally, this can be observed in paramecium).

Distribution of the Cilia and Flagella

The protozoans such as flagellates, choanoflagellates, and spermatozoa of Metazoans contain flagella. In plants, gamete cells exhibit flagellum. The cilia occur on the external body surface of some animals including Platyhelminthes, Annelids, Mollusca, Echinodermata.

Structure of Cilia and Flagella

Regardless of their different pattern of beating, cilia and flagella are equivalent structurally. All cilia and flagella are built on a typical essential plan:

Matrix

The bounded space of the cilium consists of a watery substance called matrix. In the ciliary matrix are embedded eleven microtubules of the axoneme and other adjoining proteins.

Axoneme

The axial fundamental microtubular structure of cilia and flagella is called the axoneme. It is the necessary motile element of these organelles. The axoneme is about 0.2 to 10 μm in size and may range from a few microns to 1 to 2 mm in length. The cilia might be thicker at the base and might end up being thinner slowly along the length.

The axonemal components of nearly all cilia and flagella (along with the tails of sperm cells) include the very same 9 + 2 arrangement of microtubules. In the center of the axoneme are two singlet microtubules or fibrils that run along the length of the cilium. Each of the main microtubules (25 nm in size) is composed of 13 protofilaments. The central fibrils, each have a wall of 6 nm thick and are located 35 nm away from each other. Both main fibrils are linked by a bridge and are confined in a common main sheath.

Further Reading:  Electrophoresis: Principle, Applications and Types of Electrophoresis

A plane perpendicular to the line joining the two central tubules divides the axoneme into a right and a left in symmetry half. It is typically accepted that the plane of the ciliary beat is perpendicular to this plane of symmetry.

Working of Cilia and Flagella

In eukaryotes

Using ATP produced by mitochondria near the base of the cilium or flagellum as fuel, the dynein arms push on the nearby external doublets, forcing a sliding movement to occur between adjacent outer doublets. Since the arms are activated in a stringent sequence both around and along the axoneme and since the amount of moving is limited by the radial spokes and inter-doublet links, sliding is converted into bending.

In prokaryotes

Bacterial flagella use various systems. Like the propeller of a boat, the movement of the bacterial flagellum is driven by the rotary motor at its base. The bacterial flagellum itself is a specialized piece of the extracellular cell wall, made from one protein (flagellin) that has no resemblance to tubulin or dynein. Cilia and flagella are full of cytosol all the way to their edges and utilize the ATP because cytosol produces force along their length.

Functions of Cilia and Flagella

The cilia and flagella serve many physiological activities of the cell, such as locomotion, alimentation, circulatory flow, respiration, excretion, and perception of sense.

  • Some cilia and flagella enable cells to sense changes in their environments which in turn enables the cells to react properly.
  • Some cells cannot only trap but also guide the transportation of the offered products. This might serve to swallow up such product into the cell or prevent unwanted material/particles/microorganisms from getting into the cell or tissue.
  • The eggs of amphibians and mammals are eliminated from the oviduct with the help of vibratile cilia.
  • The ciliary and flagellar movements provide the locomotion to cells or organisms like paramecium and bacteria respectively.
  • Creates food currents in aquatic animals.

MCQs about Cilia and Flagella

  1. What are Cilia and Flagella?
    • A) Non-motile projections
    • B) Filamentous cytoplasmic projections
    • C) Photosynthetic structures
    • D) Cell wall components
    • Answer: B
  2. How do cilia and flagella contribute to cell functions?
    • A) Photosynthesis
    • B) Locomotion, sensory functions, and mechanical functions
    • C) Cell division
    • D) Energy production
    • Answer: B
  3. How are cilia and flagella distinguished based on appearance?
    • A) Size and numbers
    • B) Color and shape
    • C) Length and structure
    • D) Density and arrangement
    • Answer: A
  4. Where do flagella usually occur in cells?
    • A) Throughout the cell surface
    • B) At the cell membrane
    • C) At one or two ends of the cell
    • D) Inside the nucleus
    • Answer: C
  5. What is the primary difference in movement between cilia and flagella?
    • A) Undulatory motion
    • B) Circular motion
    • C) Spiral motion
    • D) Biphasic movement
    • Answer: D
  6. Which organelle is responsible for the motile element of cilia and flagella?
  7. What is the size range of the axoneme in cilia and flagella?
    • A) 0.2 to 10 nm
    • B) 1 to 2 mm
    • C) 25 nm
    • D) 35 nm
    • Answer: A
  8. How are the axonemal components arranged in cilia and flagella?
    • A) 7 + 3 arrangement
    • B) 9 + 2 arrangement
    • C) 5 + 5 arrangement
    • D) 12 + 1 arrangement
    • Answer: B
  9. What is the function of the matrix in cilia and flagella?
    • A) Energy production
    • B) Structural support
    • C) Watery substance
    • D) Sensory perception
    • Answer: C
  10. How does the movement of cilia and flagella occur in eukaryotes?
  • A) Gravity-driven
  • B) Chemotaxis
  • C) Sliding movement
  • D) Electrical impulses
  • Answer: C
  1. What is the fuel source for the movement of cilia and flagella in eukaryotes?
  • A) Glucose
  • B) ATP produced by mitochondria
  • C) Ribosomes
  • D) Endoplasmic reticulum
  • Answer: B
  1. How do bacterial flagella move in prokaryotes?
  • A) Sliding movement
  • B) Undulatory motion
  • C) Rotary motor-driven
  • D) Contractile movement
  • Answer: C
  1. Which protein is the bacterial flagellum made from?
  • A) Tubulin
  • B) Dynein
  • C) Flagellin
  • D) Actin
  • Answer: C
  1. What physiological activities do cilia and flagella contribute to in cells?
  • A) Cell division and energy production
  • B) Locomotion, alimentation, and circulatory flow
  • C) Photosynthesis and respiration
  • D) Sensory perception and excretion
  • Answer: B
  1. In which organisms do cilia occur on the external body surface?
  • A) Plants
  • B) Protozoans
  • C) Bacteria
  • D) Fungi
  • Answer: B
  1. How are ciliary and flagellar movements involved in the removal of eggs in amphibians and mammals?
  • A) Vibratile movements
  • B) Spiral movements
  • C) Circular movements
  • D) Undulatory movements
  • Answer: A
  1. What purpose do some cilia and flagella serve in guiding transportation?
  • A) Energy production
  • B) Structural support
  • C) Trapping and guiding materials
  • D) Sensory perception
  • Answer: C
  1. Which cells use ciliary and flagellar movements for locomotion?
  • A) Plant cells
  • B) Bacterial cells
  • C) Animal cells
  • D) Fungal cells
  • Answer: C
  1. What is the size range of the axoneme in cilia and flagella?
  • A) 0.2 to 10 nm
  • B) 1 to 2 mm
  • C) 25 nm
  • D) 35 nm
  • Answer: A
  1. What is the common structural arrangement in the axoneme of cilia and flagella?
  • A) 9 + 2 arrangement
  • B) 7 + 3 arrangement
  • C) 5 + 5 arrangement
  • D) 12 + 1 arrangement
  • Answer: A
  1. In which organisms do flagella occur in gamete cells?
  • A) Plants
  • B) Protozoans
  • C) Animals
  • D) Fungi
  • Answer: B
Further Reading:  Nutrition, Respiration and Reproduction in Bacteria and Importance of Bacteria

 

Summary

In conclusion, the tutorial on Cilia and Flagella covers the microscopic, motile, filamentous projections from the cell cytoplasm, emphasizing their roles in locomotion, sensory functions, and other mechanical functions. The comparison between flagella and cilia highlights distinctions in number, length, and beating patterns. Flagella exhibit undulatory motion, while cilia demonstrate biphasic movement.

The distribution of cilia and flagella varies across organisms, with flagella found in protozoans and plant gamete cells, and cilia present on the external surfaces of certain animals. Structurally, both organelles share common elements, such as the matrix and axoneme, which consists of microtubules arranged in a 9 + 2 pattern.

The working mechanism of cilia and flagella differs in eukaryotes and prokaryotes. In eukaryotes, ATP-driven dynein arms induce sliding movements, converting them into bending. Prokaryotic bacterial flagella, on the other hand, rely on a rotary motor for propulsion.

The functions of cilia and flagella encompass various physiological activities, including locomotion, alimentation, circulatory flow, respiration, excretion, and sensory perception. They enable cells to:

  • Sense changes in their environment for proper reactions.
  • Trap and guide the transportation of substances, preventing unwanted material from entering cells or tissues.
  • Aid in the elimination of eggs from the oviduct using vibratile cilia.
  • Provide locomotion to cells or organisms, such as paramecium and bacteria, through ciliary and flagellar movements.
  • Create food currents in aquatic animals.
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