NCERT Solutions for Class 11 Biology Chapter 10: Cell Cycle and Cell Division (NCERT 2026–27)

These Class 11 Biology Chapter 10 solutions cover Cell Cycle and Cell Division with every NCERT exercise question reproduced verbatim and solved in clear, exam-ready prose. The chapter explains how a single cell duplicates its genome and divides — through the ordered phases of the cell cycle, the equational division of mitosis, and the reductional division of meiosis that produces gametes. Updated for session 2026–27.

Class: 11 Subject: Biology Chapter: 10 Name: Cell Cycle and Cell Division Exercises: 16 questions (solved) Session: 2026–27
On this page

Class 11 Biology Chapter 10 Solutions – Overview

According to the cell theory, all cells arise from pre-existing cells through cell division. Every sexually reproducing organism begins life as a single-celled zygote, and the orderly cycle of growth and division allows that one cell to build a body of millions of cells. The cell cycle is the sequence of events by which a cell duplicates its genome, synthesises other cell constituents and divides into two daughter cells. It is split into the interphase (G1, S and G2 — the preparation phase lasting over 95% of the cycle) and the M phase (mitosis). Mitosis is an equational division that conserves chromosome number, while meiosis is a reductional division that halves the chromosome number to form haploid gametes and, through crossing over, introduces the genetic variation that drives evolution.

Key Concepts & Definitions

Cell cycle: the sequence of events by which a cell duplicates its genome, synthesises other constituents and divides into two daughter cells. In a typical human cell it lasts about 24 hours.

Interphase: the “resting” preparatory phase between two M phases; divided into G1 (cell grows, no DNA replication), S (DNA replication — DNA doubles from 2C to 4C but chromosome number stays the same), and G2 (proteins synthesised, cytoplasmic growth before mitosis).

G0 (quiescent stage): an inactive stage that non-dividing cells (e.g. heart cells) enter from G1; they stay metabolically active but stop dividing.

Karyokinesis: division of the nucleus; Cytokinesis: division of the cytoplasm. Together they complete cell division.

Mitosis (equational division): nuclear division with four stages — prophase, metaphase, anaphase, telophase — producing two diploid daughter cells genetically identical to the parent.

Meiosis (reductional division): two sequential divisions (meiosis I and II) but only one round of DNA replication, producing four haploid cells; involves synapsis, crossing over and recombination.

Synapsis, bivalent & chiasmata: the pairing of homologous chromosomes (synapsis) forms a bivalent/tetrad; the X-shaped crossover points are chiasmata.

NCERT Exercises — Solutions

All questions below are reproduced verbatim from the NCERT textbook; answers are original and written in CBSE exam-ready style.

1. What is the average cell cycle span for a mammalian cell?

ANSWER The average cell cycle span for a typical mammalian cell (illustrated by human cells in culture) is about 24 hours. Within this period, the actual cell division (M phase) lasts only about 1 hour, while the interphase occupies more than 95% of the cycle. This duration varies with organism and cell type — yeast, for example, completes its cycle in about 90 minutes.

2. Distinguish cytokinesis from karyokinesis.

ANSWER
KaryokinesisCytokinesis
Division of the nucleus.Division of the cytoplasm.
Involves the separation of duplicated chromosomes into two daughter nuclei.Involves the splitting of the cell body into two daughter cells.
Occurs in four stages: prophase, metaphase, anaphase, telophase.Occurs by a furrow (animal cells) or a cell plate (plant cells).
Always precedes cytokinesis.Usually follows karyokinesis; if absent, a multinucleate syncytium forms (e.g. coconut endosperm).

3. Describe the events taking place during interphase.

ANSWER Interphase is the phase between two successive M phases during which the cell prepares for division through orderly cell growth and DNA replication. It is divided into three sub-phases: G1 phase (Gap 1): the interval between mitosis and the start of DNA replication. The cell is metabolically active and grows continuously but does not replicate its DNA. Most organelle duplication also occurs here. S phase (Synthesis): DNA replication takes place and the amount of DNA per cell doubles (from 2C to 4C), but the chromosome number does not change (a 2n cell stays 2n). In animal cells the centriole also duplicates in the cytoplasm during this phase. G2 phase (Gap 2): proteins required for mitosis are synthesised and cytoplasmic growth continues while the cell prepares to divide.

4. What is G0 (quiescent phase) of cell cycle?

ANSWER G0, the quiescent stage, is an inactive resting stage that certain cells enter by exiting the G1 phase instead of proceeding to the S phase. Cells such as heart cells, which do not divide further, and others that divide only occasionally to replace lost cells, move into G0. These cells remain metabolically active but no longer proliferate unless they are specifically signalled to divide according to the requirement of the organism.

5. Why is mitosis called equational division?

ANSWER Mitosis is called the equational division because the number of chromosomes in the parent cell and in the daughter cells remains exactly the same (equal). A diploid (2n) parent cell produces two diploid (2n) daughter cells with an identical genetic complement. This is possible because the chromosomes replicate during the S phase, and at anaphase the two sister chromatids of each chromosome separate equally into the two daughter nuclei — so the chromosome number is conserved across the division.

6. Name the stage of cell cycle at which one of the following events occur: (i) Chromosomes are moved to spindle equator. (ii) Centromere splits and chromatids separate. (iii) Pairing between homologous chromosomes takes place. (iv) Crossing over between homologous chromosomes takes place.

ANSWER (i) Metaphase (of mitosis / metaphase I of meiosis) — chromosomes align at the spindle equator (metaphase plate). (ii) Anaphase (of mitosis / anaphase II of meiosis) — centromeres split and sister chromatids separate towards opposite poles. (iii) Zygotene of Prophase I (meiosis) — homologous chromosomes pair by synapsis. (iv) Pachytene of Prophase I (meiosis) — crossing over occurs between non-sister chromatids of homologous chromosomes.

7. Describe the following: (a) synapsis (b) bivalent (c) chiasmata Draw a diagram to illustrate your answer.

ANSWER (a) Synapsis: the close, point-by-point pairing of homologous chromosomes that begins during the zygotene stage of prophase I of meiosis. This pairing is accompanied by the formation of the synaptonemal complex between the two homologues. (b) Bivalent (tetrad): the complex formed by a pair of fully synapsed homologous chromosomes. Since each homologue has two sister chromatids, a bivalent contains four chromatids and is therefore also called a tetrad; it becomes clearly visible at the pachytene stage. (c) Chiasmata: the X-shaped structures seen at the diplotene stage where the recombined homologous chromosomes begin to separate from each other but remain held together at the points where crossing over has occurred. Each chiasma marks a site of genetic exchange. Diagram: Draw two homologous chromosomes (each with two chromatids) lying side by side and overlapping at one or two points; label the side-by-side pairing as synapsis, the whole four-chromatid group as a bivalent (tetrad), and the X-shaped crossing points as chiasmata.

8. How does cytokinesis in plant cells differ from that in animal cells?

ANSWER
Cytokinesis in animal cellsCytokinesis in plant cells
Occurs by a cleavage furrow.Occurs by the formation of a cell plate.
A furrow appears in the plasma membrane, deepens and joins in the centre to divide the cell.A cell plate begins in the centre of the cell and grows outward to meet the existing lateral walls.
Division proceeds from the outside (periphery) towards the inside (centripetal).The new wall develops from the inside (centre) towards the outside (centrifugal).
No new cell wall is formed (animal cells lack a rigid wall).The cell plate forms the middle lamella between the walls of the two new cells, because the cell is enclosed by a relatively inextensible wall.

9. Find examples where the four daughter cells from meiosis are equal in size and where they are found unequal in size.

ANSWER Equal in size: During spermatogenesis (formation of male gametes) in animals, one primary spermatocyte undergoes meiosis to give four equal-sized haploid spermatids, which mature into four functional sperms. In plants, microsporogenesis (pollen formation) similarly yields four equal microspores. Unequal in size: During oogenesis (formation of the female gamete) in animals, meiosis of one primary oocyte produces a single large, functional ovum and three tiny, non-functional polar bodies — so the four daughter cells are markedly unequal in size.

10. Distinguish anaphase of mitosis from anaphase I of meiosis.

ANSWER
Anaphase of mitosisAnaphase I of meiosis
The centromere of each chromosome splits.The centromeres do not split.
Sister chromatids (daughter chromosomes) separate and move to opposite poles.Whole homologous chromosomes separate; sister chromatids stay joined at their centromeres.
Each pole receives the same number of chromosomes as the parent (no reduction).Each pole receives half the chromosome number of the parent (reduction occurs).
Daughter nuclei remain diploid.Daughter nuclei become haploid.

11. List the main differences between mitosis and meiosis.

ANSWER
MitosisMeiosis
One division of the nucleus.Two successive divisions (meiosis I and II).
One round of DNA replication followed by one division.One round of DNA replication followed by two divisions.
Produces two daughter cells.Produces four daughter cells.
Daughter cells are diploid (2n) — same number as parent.Daughter cells are haploid (n) — half the parent number.
No pairing of homologous chromosomes, no crossing over.Homologous chromosomes pair (synapsis) and undergo crossing over.
Daughter cells are genetically identical to the parent.Daughter cells are genetically different (variation).
Occurs in somatic cells; meant for growth and repair.Occurs in reproductive (germ) cells; meant for gamete formation.

12. What is the significance of meiosis?

ANSWER Meiosis is biologically very significant for two main reasons. First, it is the mechanism that conserves the specific chromosome number of a species across generations in sexually reproducing organisms: although meiosis itself halves the chromosome number (reduction division), the subsequent fusion of two haploid gametes at fertilisation restores the diploid number, keeping it constant generation after generation. Second, meiosis increases genetic variability in a population through crossing over (recombination between non-sister chromatids) and the independent assortment of chromosomes. Such variations are the raw material on which natural selection acts and are therefore essential for the process of evolution.

13. Discuss with your teacher about (i) haploid insects and lower plants where cell-division occurs, and (ii) some haploid cells in higher plants where cell-division does not occur.

ANSWER (i) In haploid insects such as the male honey bee (drone), which develops from an unfertilised egg, the haploid cells divide by mitosis to build the body and to form gametes. In many lower plants (e.g. mosses, ferns, algae), the haploid gametophyte generation grows and is maintained by repeated mitotic divisions of haploid cells — an example of mitosis occurring in the haploid phase. (ii) In higher plants, certain haploid cells do not divide further. For instance, the synergids and antipodal cells of the embryo sac, and the mature male gametes within a pollen grain, are haploid cells that normally do not undergo any further cell division; they either degenerate or function directly without dividing.

14. Can there be mitosis without DNA replication in ‘S’ phase?

ANSWER No. Mitosis cannot occur without prior DNA replication in the S phase. DNA replication during S phase produces two identical sister chromatids for each chromosome; it is these duplicated chromatids that are equally distributed to the two daughter nuclei during mitosis. Without S-phase replication there would be no sister chromatids to separate, so the two daughter cells could not each receive a complete, intact genome. Hence DNA replication is an essential prerequisite for mitosis.

15. Can there be DNA replication without cell division?

ANSWER Yes. DNA replication can occur without it being followed by cell division. When karyokinesis (and DNA replication) takes place repeatedly without cytokinesis, the cell becomes multinucleate or its DNA content (ploidy) keeps increasing. A familiar example is the formation of the multinucleate syncytium, such as the free-nuclear liquid endosperm of coconut, where nuclear divisions occur without the cell dividing into separate cells.

16. Analyse the events during every stage of cell cycle and notice how the following two parameters change (i) number of chromosomes (N) per cell (ii) amount of DNA content (C) per cell

ANSWER Taking a diploid cell with 2n chromosomes and 2C DNA at the start of G1, the two parameters change as follows:
Stage of cell cycleNumber of chromosomes (N)Amount of DNA (C)
G1 phase2n2C
S phase (DNA replicates)2n (unchanged)increases from 2C to 4C
G2 phase2n4C
Mitosis – Prophase & Metaphase2n4C
Mitosis – Anaphase (centromeres split)4n (momentarily, chromatids counted separately)4C
Mitosis – Telophase / each daughter cell2n2C
Key point: the DNA content doubles during S phase (2C → 4C) but the chromosome number stays the same until anaphase, when chromatids separate. After mitosis each daughter cell is restored to 2n and 2C. In meiosis, by contrast, two divisions follow a single S phase, so the final four cells are reduced to n chromosomes and C DNA each.

Extra Practice Questions

Short Answer Type Questions

Q1. Why is the S phase important in the cell cycle?

ANSWERDuring the S (synthesis) phase DNA replication occurs, doubling the DNA content from 2C to 4C so that each chromosome consists of two identical sister chromatids. This ensures that, after division, each daughter cell receives a complete and exact copy of the genome.

Q2. What is the synaptonemal complex and when does it form?

ANSWERThe synaptonemal complex is a protein structure that forms between paired homologous chromosomes during the zygotene stage of prophase I. It holds the homologues together during synapsis and provides the framework for crossing over.

Q3. Name the enzyme that mediates crossing over and state the stage at which it acts.

ANSWERThe enzyme is recombinase. It acts during the pachytene stage of prophase I at the recombination nodules, exchanging genetic material between non-sister chromatids of homologous chromosomes.

Q4. What is meant by the nucleo-cytoplasmic ratio, and how is it restored?

ANSWERIt is the ratio between the volume of the nucleus and that of the cytoplasm. As a cell grows, the cytoplasm increases and disturbs this ratio; the cell then divides by mitosis to restore the balanced nucleo-cytoplasmic ratio.

Q5. What is interkinesis?

ANSWERInterkinesis is the short stage between meiosis I and meiosis II. It is generally brief and, importantly, there is no DNA replication during interkinesis, after which prophase II begins.

Long Answer Type Questions

Q1. Describe the four stages of karyokinesis in mitosis.

ANSWERProphase: Chromosomal material condenses into compact chromosomes, each seen as two chromatids joined at the centromere. The centrosome (duplicated in S phase) moves to opposite poles, radiating asters; the spindle begins to form, and the golgi complex, ER, nucleolus and nuclear envelope disappear. Metaphase: The nuclear envelope completely disintegrates and chromosomes align at the equator on the metaphase plate, with spindle fibres attached to the kinetochores at the centromeres — chromosome morphology is clearest here. Anaphase: Centromeres split simultaneously and the two daughter chromatids (now daughter chromosomes) migrate to opposite poles, centromeres leading and arms trailing. Telophase: Chromosomes reach the poles, decondense and lose their identity; nuclear envelopes form around each cluster, and the nucleolus, golgi complex and ER reform, producing two daughter nuclei.

Q2. Explain the five sub-stages of prophase I of meiosis.

ANSWERLeptotene: chromosomes gradually become visible and begin to condense. Zygotene: homologous chromosomes pair by synapsis and the synaptonemal complex forms, creating bivalents. Pachytene: bivalents appear clearly as tetrads of four chromatids; recombination nodules appear and crossing over (exchange of genetic material via recombinase) occurs between non-sister chromatids. Diplotene: the synaptonemal complex dissolves and homologues separate except at the X-shaped chiasmata (sites of crossover). Diakinesis: chiasmata terminalise, chromosomes are fully condensed, the meiotic spindle assembles, and the nucleolus and nuclear envelope break down, marking the transition to metaphase I.

Q3. Discuss the significance of mitosis in the life of an organism.

ANSWERMitosis produces diploid daughter cells with an identical genetic complement, ensuring genetic stability. It is responsible for the growth of multicellular organisms, allowing a single zygote to develop into a body of millions of cells. It restores the nucleo-cytoplasmic ratio that is disturbed as a cell grows. A very significant role is cell repair and replacement — the cells of the upper epidermis, the gut lining and blood cells are continually renewed by mitosis. In plants, mitotic divisions in the meristematic tissues (apical and lateral cambium) bring about continuous growth throughout the plant’s life.

MCQs & Assertion–Reason

1. The interphase of a typical human cell cycle lasts about:

(a) 50% of the cycle    (b) less than 5%    (c) more than 95%    (d) exactly 1 hour

2. DNA replication takes place during which phase?

(a) G1 phase    (b) S phase    (c) G2 phase    (d) M phase

3. Cells that stop dividing exit G1 to enter:

(a) S phase    (b) G2 phase    (c) G0 (quiescent) stage    (d) prophase

4. Chromosomes align at the metaphase plate during:

(a) prophase    (b) metaphase    (c) anaphase    (d) telophase

5. Splitting of centromeres and separation of chromatids occurs in:

(a) prophase    (b) metaphase    (c) anaphase    (d) telophase

6. Crossing over between homologous chromosomes occurs at:

(a) leptotene    (b) zygotene    (c) pachytene    (d) diakinesis

7. Synapsis (pairing of homologous chromosomes) begins during:

(a) leptotene    (b) zygotene    (c) diplotene    (d) diakinesis

8. The X-shaped structures seen at diplotene are called:

(a) bivalents    (b) kinetochores    (c) chiasmata    (d) asters

9. Number of daughter cells produced at the end of meiosis is:

(a) two diploid    (b) two haploid    (c) four haploid    (d) four diploid

10. Cytokinesis in plant cells is achieved by:

(a) cleavage furrow    (b) cell plate formation    (c) constriction ring    (d) budding

Answer key: 1-(c), 2-(b), 3-(c), 4-(b), 5-(c), 6-(c), 7-(b), 8-(c), 9-(c), 10-(b).

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: Mitosis is called equational division.

Reason: The chromosome number of the parent cell is conserved in the daughter cells.

A-R 2. Assertion: During the S phase the chromosome number doubles.

Reason: DNA replication takes place during the S phase.

A-R 3. Assertion: Meiosis increases genetic variability in a population.

Reason: Crossing over and recombination occur during prophase I of meiosis.

A-R 4. Assertion: Cells in the G0 stage are metabolically inactive and dead.

Reason: G0 cells permanently lose the ability to respond to any signal.

A-R 5. Assertion: There is no DNA replication during interkinesis.

Reason: Meiosis involves two divisions but only a single round of DNA replication.

Answer key: 1-(A), 2-(C), 3-(A), 4-(D), 5-(A).

Common Mistakes to Avoid

Watch out for these

  • Saying the chromosome number doubles in S phase — only the DNA content doubles (2C → 4C); the chromosome number stays the same.
  • Confusing karyokinesis (nuclear division) with cytokinesis (cytoplasmic division).
  • Stating that centromeres split in anaphase I of meiosis — they do not; only homologous chromosomes separate while sister chromatids stay joined.
  • Mixing up the order of prophase I sub-stages — remember L Z P D D: Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis.
  • Thinking G0 cells are dead — they are alive and metabolically active, just not dividing.
  • Writing that plant cells divide by a furrow — plant cells use a cell plate that grows from the centre outward.

How to score full marks in this chapter

Learn the cell-cycle parameters as a small table (N and C at G1, S, G2, anaphase, telophase) — one-mark numericals are guaranteed. Memorise the five prophase-I sub-stages in order and pair each with its event (zygotene = synapsis, pachytene = crossing over, diplotene = chiasmata). For difference-based questions (mitosis vs meiosis, anaphase vs anaphase I, plant vs animal cytokinesis), always answer in a two-column table. Use exact NCERT terms — equational/reductional division, synaptonemal complex, recombinase, kinetochore, metaphase plate — to earn keyword marks.

Frequently Asked Questions

What is Class 11 Biology Chapter 10 about?

Chapter 10, Cell Cycle and Cell Division, explains the cell cycle (interphase with G1, S, G2, and the M phase), the four stages of mitosis (equational division), and meiosis (reductional division with meiosis I and II), along with their significance in growth, repair, gamete formation and evolution.

What is the difference between mitosis and meiosis in short?

Mitosis is a single division producing two genetically identical diploid cells for growth and repair, with no pairing or crossing over. Meiosis involves two divisions after one DNA replication, producing four genetically different haploid cells (gametes), and includes synapsis and crossing over.

Why does the DNA content double but the chromosome number stays the same in S phase?

During the S phase each chromosome is copied to form two identical sister chromatids joined at the centromere. The DNA amount therefore doubles (2C to 4C), but since the two chromatids stay attached, they still count as one chromosome — so the chromosome number is unchanged until they separate at anaphase.

Are these Class 11 Biology Chapter 10 solutions free?

Yes. All solutions are free and follow the official NCERT Biology textbook for session 2026–27, with every exercise question solved.

← Chapter 9: Biomolecules All Biology Chapters Chapter 11: Photosynthesis in Higher Plants →
Scroll to Top