Cilia and Flagella: Structure, Function & 9+2 Arrangement (NEET Notes)

 Cilia vs Flagella: Easy NEET Biology Notes with Diagram & Mind Map 

Structure of cilia and flagella showing the 9+2 microtubule arrangement and basal body in a eukaryotic cell.

- Dr. Sanjay Kumar Pawar 

Cilia and Flagella – Basic Idea

• Cilia and flagella are hair-like structures present on the surface of the cell.
• They are extensions of the cell membrane.

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Cilia

• Cilia are short and numerous hair-like structures.
• They move in a coordinated, oar-like motion (like rowing a boat).
• Function:
  • Help in movement of the cell (e.g., Paramecium).
  • Or move fluid/particles around the cell (e.g., in respiratory tract).

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Flagella

• Flagella are long, whip-like structures.
• Usually present in fewer numbers (1 or 2 per cell).
• Function:
  • Responsible for movement of the whole cell (e.g., sperm cell).

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Difference between Prokaryotic and Eukaryotic Flagella

• Prokaryotic flagella (bacteria):
  • Structurally different from eukaryotic flagella.
• Eukaryotic flagella:
  • Have a complex microtubule structure.

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Structure (Electron Microscope View)

• Cilia and flagella are covered by the plasma membrane.
• Inside is a core called the axoneme.

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Axoneme Structure

• Axoneme contains microtubules (tubulin protein tubes).
• These microtubules run parallel to the long axis of cilium/flagellum.

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9 + 2 Arrangement (Very Important for NEET)

• Axoneme shows a special pattern called 9 + 2 arrangement:
  • 9 peripheral microtubule doublets arranged in a circle.
  • 2 single central microtubules in the center.

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Details of 9 + 2 Structure

• Central two microtubules:

  • Surrounded by a central sheath.
  • Connected to each other by bridges.

• Peripheral microtubules:

  • Each doublet is connected to central sheath by radial spokes.
  • Total 9 radial spokes present.

• Peripheral doublets are:

  • Interconnected by linker proteins.

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Basal Body (Important Point)

• Both cilia and flagella arise from a structure called the basal body.
• Basal body is similar to a centriole in structure.

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Quick NEET Revision Points

• Cilia = short, many, movement of fluid/cell
• Flagella = long, few, movement of cell
• Core = axoneme
• Key pattern = 9 + 2 microtubule arrangement
• Origin = basal body (centriole-like)

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Cilia and Flagella
├── Definition
│ ├── Hair-like outgrowths of cell membrane
│ ├── Made of microtubules
│
├── Cilia
│ ├── Short, numerous
│ ├── Beat like oars
│ ├── Function
│ │ ├── Move cell (e.g., Paramecium)
│ │ └── Move fluid over cell surface (e.g., respiratory tract)
│
├── Flagella
│ ├── Long, few (1–2 per cell)
│ ├── Whip-like movement
│ ├── Function
│ │ └── Movement of entire cell (e.g., sperm)
│
├── Structure
│ ├── Covered by plasma membrane
│ ├── Core = Axoneme
│ │ ├── Microtubules arranged longitudinally
│ │ ├── 9 + 2 arrangement
│ │ │ ├── 9 peripheral microtubule doublets
│ │ │ └── 2 central microtubules
│ │ ├── Central pair
│ │ │ ├── Connected by bridges
│ │ │ └── Surrounded by central sheath
│ │ ├── Radial spokes
│ │ │ └── Connect peripheral doublets to central sheath
│ │ └── Linkers between peripheral doublets
│
├── Basal Body
│ ├── Origin of cilia and flagella
│ ├── Similar to centriole
│
└── Key Difference (Prokaryote vs Eukaryote)
├── Prokaryotic flagella → structurally different
└── Eukaryotic flagella → 9 + 2 microtubules structure 

Internal Links

/cell-structure

/cell-organelles-notes

/microtubules-and-cytoskeleton

/neat-biology-notes

/eukaryotic-cell-structure

/difference-between-cilia-and-flagella

/biology-diagrams-for-neet

/axoneme-structure-explained

Cilia and Flagella - Complete Question Bank (Class 11 CBSE)

Very Short Answer Questions

Q1. What are cilia and flagella?

Ans: Hair-like outgrowths of the cell membrane involved in movement.

Q2. What is the core of cilia and flagella called?

Ans: Axoneme.

Q3. What is the basic structural pattern of axoneme?

Ans: 9 + 2 arrangement.

Q4. From where do cilia and flagella arise?

Ans: Basal body.

Q5. Name a protein found in microtubules.

Ans: Tubulin.

Short Answer Questions

Q1. Differentiate between cilia and flagella.

Ans: Cilia are short and numerous, help in movement of fluid or cell. Flagella are long and few, help in movement of the whole cell.

Q2. Write any two functions of cilia.

Ans: Movement of cell (Paramecium) and movement of mucus in respiratory tract.

Q3. What is 9 + 2 arrangement?

Ans: It is the arrangement of microtubules in axoneme with 9 peripheral doublets and 2 central microtubules.

Q4. What is basal body?

Ans: A centriole-like structure from which cilia and flagella arise.

Long Answer Questions

Q1. Explain the structure of cilia and flagella.

Ans:
- Covered by plasma membrane
- Core is axoneme
- 9 + 2 microtubule arrangement
- 9 peripheral doublets
- 2 central microtubules
- Central pair connected by bridges
- Surrounded by central sheath
- Radial spokes connect central sheath to peripheral doublets
- Peripheral doublets connected by linkers
- Arise from basal body

Q2. Explain functions of cilia and flagella.

Ans:
- Cilia help in movement of cell and fluid
- Flagella help in locomotion of cell
- Cilia remove dust in respiratory tract
- Flagella help sperm movement

MCQs

Q1. Axoneme shows which arrangement?

Ans: B. 9 + 2

Q2. Cilia and flagella arise from?

Ans: C. Basal body

Q3. Microtubule protein is?

Ans: C. Tubulin

Q4. Cilia mainly help in?

Ans: B. Movement of cell or fluid

Q5. Flagella are?

Ans: B. Long and few

Fill in the Blanks

Q1. Axoneme shows ______ arrangement.

Ans: 9 + 2

Q2. Cilia and flagella are covered by ______ membrane.

Ans: Plasma

Q3. Microtubules are made of ______.

Ans: Tubulin

Q4. Basal body is similar to ______.

Ans: Centriole

Assertion and Reason

Q1.

Assertion: Cilia and flagella have 9 + 2 arrangement.
Reason: It consists of 9 peripheral doublets and 2 central microtubules.
Ans: Both are true and Reason explains Assertion.

Q2.

Assertion: Flagella are longer than cilia.
Reason: Flagella help in movement of whole cell.
Ans: Both are true but Reason does not explain Assertion.

Match the Following

Cilia → Short structures
Flagella → Long structures
Axoneme → 9 + 2 arrangement
Basal body → Centriole-like
Tubulin → Microtubule protein

Case Study

Passage:

Cilia and flagella are cell organelles involved in movement. They have axoneme with 9 + 2 arrangement and arise from basal bodies.

Questions & Answers:

Q1. Core of cilia and flagella? Ans: Axoneme
Q2. Arrangement? Ans: 9 + 2
Q3. Origin? Ans: Basal body
Q4. Covering? Ans: Plasma membrane
Q5. Protein? Ans: Tubulin