Centerioles | Centerioles structure and function | class 11
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Notes
Centrioles
#### 1. Definition and Occurrence
Centrioles are non-membranous cell organelles found mainly in animal cells.
They are also found in fungi-like protists such as slime molds and water molds.
#### 2. Structure
Centrioles are rod-shaped structures and usually occur in pairs.
These pairs occur at right angles to each other near one pole of the nucleus.
Each centriole is composed of nine triplets of microtubules circularly arranged around a central axis.
#### 3. Role in Cell Division
Just before cell division, the pair of centrioles duplicates, becoming two pairs.
These pairs then migrate to opposite sides of the nucleus.
Both centriole pairs give rise to microtubules, also known as spindle fibers, during cell division.
The entire structure of spindle fibers is known as the mitotic apparatus.
The mitotic apparatus helps in the distribution of chromosomes between the daughter cells during cell division.
#### 4. Additional Functions
Centrioles also give rise to basal bodies of cilia and flagella.
MCQs
Important MCQs
1. *Where are centrioles primarily found?*
A) Plant cells
B) Animal cells
C) Bacterial cells
D) Viruses
*Answer:* B) Animal cells
2. *What is the typical shape of centrioles?*
A) Spherical
B) Rod-shaped
C) Cuboidal
D) Flat
*Answer:* B) Rod-shaped
3. *How are the microtubules arranged within a centriole?*
A) In pairs
B) In quadruplets
C) In triplets
D) In doublets
*Answer:* C) In triplets
4. *What structure do centrioles help form during cell division?*
A) Chromosomes
B) Ribosomes
C) Spindle fibers
D) Plasma membrane
*Answer:* C) Spindle fibers
5. *What is the name of the entire structure formed by spindle fibers during cell division?*
A) Cytoskeleton
B) Mitotic apparatus
C) Chromatin
D) Nuclear envelope
*Answer:* B) Mitotic apparatus
6. *Centrioles give rise to which of the following structures?*
A) Lysosomes
B) Basal bodies of cilia and flagella
C) Golgi apparatus
D) Mitochondria
*Answer:* B) Basal bodies of cilia and flagella
7. *The cytoskeleton is a network of fibers that extends from the nucleus to the:*
A) Endoplasmic reticulum
B) Plasma membrane
C) Mitochondria
D) Golgi apparatus
*Answer:* B) Plasma membrane
8. *Which of the following is NOT a component of the cytoskeleton?*
A) Microfilaments
B) Microtubules
C) Intermediate filaments
D) Ribosomes
*Answer:* D) Ribosomes
9. *What are microfilaments composed of?*
A) Actin
B) Tubulin
C) Keratin
D) Collagen
*Answer:* A) Actin
10. *Which cytoskeletal component is primarily responsible for maintaining the cell's shape?*
A) Microfilaments
B) Microtubules
C) Intermediate filaments
D) All of the above
*Answer:* D) All of the above