Chapter 10: Cell Cycle and Cell Division Short Questions | biology Class 11 CBSE

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Chapter 10: Cell Cycle and Cell Division Short Questions | biology Class 11 CBSE | ByteNotes.in

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Question 1

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What is the cell cycle? State the two basic phases into which it is divided.

The cell cycle is the sequence of events by which a cell duplicates its genome, synthesises cellular constituents, and eventually divides into two daughter cells.
The two basic phases are Interphase (preparation phase) and M Phase (Mitosis phase, when actual division occurs).
In a human cell with a 24-hour cycle, the M phase lasts only about an hour while interphase occupies more than 95% of the cycle duration.

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Question 2

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Describe the events that occur during the G1 phase of interphase.

G1 phase (Gap 1) corresponds to the interval between mitosis and the initiation of DNA replication.
During G1, the cell is metabolically active and grows continuously, but does not replicate its DNA.
Cells that do not need to divide further exit G1 to enter the quiescent stage G0, remaining metabolically active but non-proliferating.

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Question 3

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What changes in DNA content occur during the S phase of the cell cycle?

During S phase (Synthesis phase), DNA synthesis or replication takes place, doubling the amount of DNA per cell.
If the initial DNA content is 2C, after S phase it becomes 4C.
Importantly, despite doubling of DNA content, the chromosome number does not increase — a cell with 2n chromosomes at G1 still has 2n chromosomes after S phase.

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Question 4

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What is the G0 stage of the cell cycle? Give one example of a cell type that enters G0.

G0 is the quiescent (inactive) stage of the cell cycle, entered by cells that exit G1 and no longer proliferate.
Cells in G0 remain metabolically active but do not divide further unless required by the organism.
Heart cells in adult animals are an example of cells that enter the G0 stage and do not normally divide.

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Question 5

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Why is mitosis called equational division?

Mitosis is called equational division because the chromosome number in the parent cell and the progeny (daughter) cells remains the same.
A diploid parent cell with 2n chromosomes produces two daughter cells, each also with 2n chromosomes.
Unlike meiosis which reduces chromosome number, mitosis maintains the genetic complement, hence the term 'equational'.

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Question 6

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List the key events that occur during prophase of mitosis.

Chromosomal material condenses to form compact mitotic chromosomes, each composed of two chromatids attached at the centromere.
The centrosome, which duplicated during interphase, begins to move towards opposite poles; each centrosome radiates microtubules called asters forming the mitotic apparatus.
By the end of prophase, the Golgi complexes, endoplasmic reticulum, nucleolus, and nuclear envelope disappear from view.

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Question 7

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What is the role of kinetochores during metaphase of mitosis?

Kinetochores are small disc-shaped structures located at the surface of centromeres of chromosomes.
During metaphase, kinetochores serve as the sites of attachment of spindle fibres from the opposite poles.
Through this attachment, chromosomes are moved to and aligned at the spindle equator, forming the metaphase plate.

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Question 8

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Describe the key events of anaphase of mitosis.

At the onset of anaphase, each chromosome at the metaphase plate splits simultaneously as the centromere divides.
The two daughter chromatids (now called daughter chromosomes) begin their migration towards the two opposite poles.
As chromosomes move, the centromere remains directed towards the pole at the leading edge, with chromosome arms trailing behind.

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Question 9

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What events characterise telophase of mitosis?

Chromosomes that have reached their respective poles decondense and lose their individuality; they can no longer be seen as discrete elements.
Nuclear envelopes develop around the chromosome clusters at each pole, forming two distinct daughter nuclei.
The nucleolus, Golgi complex, and endoplasmic reticulum reform during telophase.

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Question 10

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How does cytokinesis differ in plant cells compared to animal cells?

In animal cells, cytokinesis occurs by formation of a cleavage furrow in the plasma membrane that gradually deepens until the cytoplasm is divided into two.
In plant cells, due to the inextensible cell wall, cytokinesis occurs by formation of a cell-plate at the centre of the cell that grows outward to meet the lateral walls.
The cell-plate represents the future middle lamella between the walls of the two adjacent daughter cells.

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Question 11

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What is syncytium? How is it formed? Give an example.

Syncytium is a multinucleate condition arising in cells where karyokinesis (nuclear division) is not followed by cytokinesis (cytoplasmic division).
When multiple rounds of nuclear division occur without cell wall or membrane formation, a single cytoplasm contains many nuclei.
The liquid endosperm in coconut is a classic example of a syncytium.

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Question 12

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State two significant contributions of mitosis to the life of multicellular organisms.

Mitosis is responsible for growth of multicellular organisms by increasing cell numbers while maintaining identical genetic complements in daughter cells.
Mitosis plays a vital role in cell repair and replacement — cells of the upper epidermis, gut lining, and blood cells are constantly replaced by mitotic divisions.
Mitotic divisions restore the nucleo-cytoplasmic ratio that gets disturbed during cell growth.

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Question 13

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What is meiosis? State two of its key features that distinguish it from mitosis.

Meiosis is a specialised type of cell division that reduces the chromosome number by half, producing four haploid daughter cells from a single diploid parent cell.
Unlike mitosis, meiosis involves two sequential rounds of division (Meiosis I and Meiosis II) but only a single cycle of DNA replication.
Meiosis involves pairing of homologous chromosomes and crossing over (genetic recombination) between non-sister chromatids, which does not occur in mitosis.

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Chapter 10: Cell Cycle and Cell Division | Short Questions

What is the cell cycle? State the two basic phases into which it is divided.

Describe the events that occur during the G1 phase of interphase.

What changes in DNA content occur during the S phase of the cell cycle?

What is the G0 stage of the cell cycle? Give one example of a cell type that enters G0.

Why is mitosis called equational division?

List the key events that occur during prophase of mitosis.

What is the role of kinetochores during metaphase of mitosis?

Describe the key events of anaphase of mitosis.

What events characterise telophase of mitosis?

How does cytokinesis differ in plant cells compared to animal cells?

What is syncytium? How is it formed? Give an example.

State two significant contributions of mitosis to the life of multicellular organisms.

What is meiosis? State two of its key features that distinguish it from mitosis.

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