Centrosome and Centrioles Notes for NEET 2026 | Structure, Functions & Diagram

 Centrosome and Centrioles NEET Notes: 9×3 Arrangement Explained 

Structure of centrosome and centriole showing the characteristic 9×3+0 microtubule arrangement and cartwheel organization.

- Dr.Sanjaykumar Pawar 

Centrosome and Centrioles 

Centrosome

1. Centrosome is a cell organelle present mainly in animal cells.
2. It is located near the nucleus.
3. A centrosome usually contains two centrioles.
4. The two centrioles are surrounded by a protein-rich material called pericentriolar material (PCM).
5. The centrosome acts as the microtubule-organizing centre (MTOC) of the cell.
6. It helps in the formation of spindle fibres during cell division.

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Structure of Centrioles

1. Centrioles are cylindrical structures.
2. The two centrioles in a centrosome are arranged perpendicular (90°) to each other.
3. Each centriole shows a cartwheel-like arrangement.
4. A centriole is made up of nine peripheral fibrils.
5. These fibrils are composed of tubulin protein.
6. Each peripheral fibril consists of three microtubules, therefore called a triplet.
7. Thus, the arrangement is called 9 × 3 arrangement (9 triplets).
8. There are no microtubules in the centre of the centriole.
9. Adjacent triplets are connected with each other by protein linkers.

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Cartwheel Structure

1. The central region of the proximal part contains a protein structure called the hub.
2. The hub is present at the centre of the cartwheel.
3. The hub is connected to peripheral triplets by radial spokes.
4. Both the hub and spokes are made of protein.
5. This arrangement gives the centriole its characteristic cartwheel appearance.

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Functions of Centrioles and Centrosome

1. Centrioles help in the formation of basal bodies.
2. Basal bodies give rise to cilia and flagella.
3. Centrosomes organize microtubules in the cell.
4. They form spindle fibres during cell division.
5. Spindle fibres together form the spindle apparatus.
6. The spindle apparatus helps in the equal distribution of chromosomes during cell division.
7. Therefore, centrosomes play an important role in mitosis and meiosis.

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NEET Important Points (One-Liners)

• Centrosome = Two centrioles + pericentriolar material (PCM).
• Centrioles are usually present in animal cells.
• Two centrioles are arranged at right angles (90°).
• Centriole shows 9 triplet microtubules (9 × 3 arrangement).
• Centriole has no central microtubules.
• Microtubules are made of tubulin protein.
• Central proteinaceous region = Hub.
• Hub is connected to triplets by radial spokes.
• Centrioles form basal bodies of cilia and flagella.
• Centrosome forms spindle fibres during cell division.

NEET Memory Trick

"Centriole = 9 Triplets, No Centre"

➡️ Centriole → 9 × 3 + 0 arrangement
➡️ Cilia/Flagella (axoneme) → 9 + 2 arrangement (different from centriole)

This distinction is frequently asked in NEET.

CENTROSOME & CENTRIOLES

│

├── Centrosome

│   │

│   ├── Present mainly in animal cells

│   ├── Located near nucleus

│   ├── Contains two centrioles

│   ├── Surrounded by pericentriolar material (PCM)

│   └── Functions

│       ├── Organizes microtubules

│       ├── Forms spindle fibres

│       └── Helps in cell division

│

├── Centrioles

│   │

│   ├── Cylindrical structures

│   ├── Two centrioles arranged at 90°

│   ├── Cartwheel-like organization

│   └── Made of tubulin protein

│

├── Structure of Centriole

│   │

│   ├── 9 peripheral fibrils

│   ├── Each fibril = 3 microtubules

│   │   └── Called triplet

│   ├── Arrangement = 9 × 3 + 0

│   ├── No central microtubules

│   └── Adjacent triplets linked together

│

├── Cartwheel Structure

│   │

│   ├── Central hub (proteinaceous)

│   ├── Hub present in proximal region

│   ├── Radial spokes arise from hub

│   └── Spokes connect hub to triplets

│

├── Functions of Centrioles

│   │

│   ├── Form basal bodies

│   ├── Give rise to cilia

│   ├── Give rise to flagella

│   └── Participate in spindle formation

│

└── NEET Quick Facts

    │

    ├── Centrosome = 2 Centrioles + PCM

    ├── Centriole = 9 triplets, no centre

    ├── Protein of microtubules = Tubulin

    ├── Central region = Hub

    ├── Hub connected by radial spokes

    ├── Forms basal bodies

    └── Forms spindle apparatus during cell division

MEMORY TRICK

Centriole → 9 × 3 + 0

Cilia/Flagella (Axoneme) → 9 + 2 

 Internal Links

Cell: The Unit of Life Notes for NEET

Cell Organelles Complete Revision Notes

Microtubules, Microfilaments and Cytoskeleton

Cilia and Flagella Structure Explained

Cell Cycle and Cell Division Notes

Mitosis and Meiosis Comparison

Animal Cell vs Plant Cell Differences

Biomolecules Notes for NEET

Nucleus Structure and Functions

NEET Biology Chapter-wise Revision Notes

CBSE Class 11 Biology

Centrosome and Centrioles - Question Bank with Answers

A. Multiple Choice Questions (MCQs)

1. The centrosome is mainly found in:

a) Plant cells
b) Animal cells
c) Fungal cells
d) Bacterial cells

Answer: b) Animal cells

2. A centrosome usually contains:

a) One centriole
b) Two centrioles
c) Three centrioles
d) Four centrioles

Answer: b) Two centrioles

3. The two centrioles are arranged at:

a) 45°
b) 60°
c) 90°
d) 180°

Answer: c) 90°

4. Microtubules are made of:

a) Actin
b) Myosin
c) Tubulin
d) Keratin

Answer: c) Tubulin

5. The arrangement of microtubules in a centriole is:

a) 9+2
b) 9+0
c) 9×3+0
d) 13+2

Answer: c) 9×3+0

B. Very Short Answer Questions

1. What is a centrosome?

Answer: Centrosome is a cell organelle containing two centrioles surrounded by pericentriolar material (PCM).

2. Where is the centrosome located?

Answer: Near the nucleus.

3. Name the protein present in microtubules.

Answer: Tubulin.

4. How many triplets are present in a centriole?

Answer: Nine triplets.

5. What is PCM?

Answer: Pericentriolar Material.

C. Short Answer Questions

1. Define centrosome and mention its components.

Answer:

• Centrosome is a cell organelle present mainly in animal cells.
• It contains two centrioles.
• The centrioles are surrounded by pericentriolar material (PCM).

2. Describe the arrangement of centrioles.

Answer:

• Centrioles are cylindrical structures.
• Two centrioles are arranged perpendicular to each other.
• Each centriole contains nine triplet microtubules.
• The arrangement is called 9 × 3 + 0.

3. What is the cartwheel structure?

Answer:

• The cartwheel structure contains a central hub.
• Radial spokes arise from the hub.
• The spokes connect the hub to peripheral triplet microtubules.

D. Long Answer Questions

1. Explain the structure and functions of centrioles.

Structure:

• Centrioles are cylindrical organelles.
• Present in pairs inside the centrosome.
• Arranged at right angles (90°).
• Made up of nine peripheral triplet microtubules.
• Show a 9 × 3 + 0 arrangement.
• Contain a cartwheel structure with hub and radial spokes.

Functions:

• Form basal bodies.
• Give rise to cilia and flagella.
• Participate in spindle fibre formation.
• Help in chromosome movement during cell division.

2. Explain the structure and functions of centrosome.

Structure:

• Located near the nucleus.
• Contains two centrioles.
• Surrounded by pericentriolar material (PCM).
• Acts as the microtubule-organizing centre (MTOC).

Functions:

• Organizes microtubules.
• Forms spindle fibres.
• Produces spindle apparatus.
• Helps in mitosis and meiosis.
• Ensures equal chromosome distribution.

E. Assertion and Reason Questions

1. Assertion (A): Centrioles have a 9 × 3 arrangement.
Reason (R): Each peripheral fibril consists of three microtubules.

Answer: Both A and R are true and R is the correct explanation of A.

2. Assertion (A): Centrosomes are important during cell division.
Reason (R): They form spindle fibres.

Answer: Both A and R are true and R is the correct explanation of A.

3. Assertion (A): Centrioles contain central microtubules.
Reason (R): Centrioles show a 9 × 3 + 0 arrangement.

Answer: Assertion is false but Reason is true.

F. Fill in the Blanks

1. Centrosome contains ______ centrioles. Answer: Two
2. Microtubules are made of ______ protein. Answer: Tubulin
3. The central region of cartwheel is called ______. Answer: Hub
4. Centrioles show ______ arrangement. Answer: 9 × 3 + 0
5. Centrioles help in the formation of ______ bodies. Answer: Basal

G. Match the Columns

Column A	Column B
PCM	Pericentriolar Material
Microtubule	Tubulin Protein
Centriole	9 × 3 Arrangement
Basal Body	Formation of Cilia and Flagella

Answers

PCM → Pericentriolar Material
Microtubule → Tubulin Protein
Centriole → 9 × 3 Arrangement
Basal Body → Formation of Cilia and Flagella

H. Case Study Questions

A student observed a cell organelle near the nucleus containing two cylindrical structures arranged at right angles. Each cylindrical structure had nine triplet microtubules made of tubulin protein. The organelle was involved in spindle formation during cell division.

1. Name the organelle.

Answer: Centrosome

2. Name the cylindrical structures.

Answer: Centrioles

3. What is the arrangement of microtubules?

Answer: 9 × 3 + 0 arrangement

4. Which protein forms these microtubules?

Answer: Tubulin

5. Mention one function of the organelle.

Answer: Formation of spindle fibres during cell division.

I. Statement Based Questions

1. Centrioles are present mainly in animal cells. Answer: True

2. A centriole contains nine doublet microtubules. Answer: False

3. PCM surrounds centrioles. Answer: True

4. Hub is connected to triplets by radial spokes. Answer: True

5. Basal bodies form cilia and flagella. Answer: True

Quick Revision

• Centrosome = 2 Centrioles + PCM
• Centriole = 9 × 3 + 0 arrangement
• Microtubule protein = Tubulin
• Central region = Hub
• Hub connected by radial spokes
• Basal bodies form cilia and flagella
• Centrosome forms spindle fibres during cell division
• Two centrioles are arranged at 90°