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State Board · Class 11 · Biology

Lesson 7: Cell Division

7 concepts · 56 practice questions with answers · Free to read

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Cell cycle and interphase

Link to Std 9–10

This is the detailed stage of the simple mitosis and meiosis of Std 9–10, taking each phase in order.

From daily life

Before a building rises, the foundation, materials and plan are ready; likewise a cell grows, doubles DNA and prepares before dividing: the interphase.

Simple definition

Cell cycle = the sequence of events in a dividing cell: interphase (G1, S, G2) and M-phase (karyokinesis + cytokinesis). Interphase is the longest phase.

Phases of the cell cycleG18 h+S6–8 hG22–5 hM1–3 hCell cycleInterphase = G1 + S + G2G1growth; RNA, protein, membraneSDNA replication (doubles); histonesG2nucleus grows; division proteinsMKaryokinesis + cytokinesisG0resting / non-dividing stateInterphase = the longest phaseDNA doubles in S; chromosome number sameCentriole pair duplicates (animal cells)‘M’ = mitosis or meiosis

In the figure : Cell cycle: G1 (8 h+), S (6–8), G2 (2–5), M (1–3) and G0.

Rule 1 : Three parts of interphase — G1 (first gap): cell grows; mRNA, rRNA, tRNA, proteins and membranes made. S (synthesis): DNA replication – DNA doubles, histones made. G2: nucleus grows; division proteins made; a new centriole pair appears in animal cells.

  • Easy : S doubles DNA, but chromosome number stays the same.
  • Medium : G1 + S + G2 = interphase; M = division.
  • Exam-type (CET) : G0 = resting non-dividing state (e.g. neurons).

Rule 2 : M-phase — ‘M’ = mitosis or meiosis. Two parts: karyokinesis = nuclear division (two nuclei) and cytokinesis = cytoplasmic division (two cells). A multicellular organism begins from a single zygote; growth depends on cell division.

  • Easy : Karyo = nucleus; cyto = cytoplasm.
  • Medium : M-phase is the shortest (1–3 h).
  • Exam-type (CET) : ‘Every cell from a cell’ – Virchow; growth and wound healing by division.
Remember

G1 growth; S DNA replication; G2 preparation; M division.

Common mistake and CET trap

‘Chromosome number doubles in S’ is wrong (DNA doubles). Trap: ‘interphase = rest’ is wrong (highly active).

Shortcut

Memory clue : "G1 = Grow, S = Synthesise DNA, G2 = Get ready, M = Multiply".

Spot the difference

PhaseEventDuration
G1Growth, RNA, protein8 h+
SDNA replication6–8 h
G2Nucleus grows2–5 h

Practice questions

Easy
  1. 1Two main phases of the cell cycle.
  2. 2Three subphases of interphase.
  3. 3In which phase does DNA replicate?
Medium
  1. 4When are histones made?
  2. 5Define karyokinesis and cytokinesis.
  3. 6What is G0 phase?
Challenging
  1. 7Why is interphase the longest?
  2. 8Difference between S and G2.
Show answers (try them yourself first)
  1. 1Interphase and M-phase.
  2. 2G1, S, G2.
  3. 3S-phase.
  4. 4In S-phase.
  5. 5Nuclear division / cytoplasmic division.
  6. 6A resting state where the cell stops dividing.
  7. 7Growth, DNA replication and preparation need time.
  8. 8S doubles DNA; G2 makes division proteins and enlarges nucleus.

Types of division; prophase and metaphase of mitosis

From daily life

A wound heals as nearby cells make new cells by mitosis; but sperm and eggs need a different division – meiosis.

Simple definition

Three kinds: amitosis (direct), mitosis (indirect, 2 identical cells), meiosis (reductional). Mitosis: prophase, metaphase, anaphase, telophase + cytokinesis.

Division types; prophase and metaphaseThree kinds of cell divisionAmitosisMitosisMeiosisdirect; nucleus pinchesbacteria, old cellsindirect; 2 identical cellsbody growthreductional; 4 haploid cellsreproductive cellsProphaseMetaphasechromosomes condense; envelope fadescentrosomes move to poleschromosomes at the equatorspindle fibres on centromeres

In the figure : Three kinds of division; prophase and metaphase of mitosis.

Live figure

Types of division; prophase and metaphase of mitosis

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Rule 1 : Types of division — Amitosis: nucleus elongates and constricts, unequal halves; bacteria, old cells, foetal membranes. Mitosis: in haploid and diploid cells. Meiosis: only in diploid cells. E.g. honey-bee drones from haploid eggs; Marchantia spores form gametophyte by mitosis.

  • Easy : Amitosis = simplest; no spindle.
  • Medium : Mitosis = equational (number unchanged).
  • Exam-type (CET) : Meiosis = reductional (number halved).

Rule 2 : Prophase and metaphase — Prophase: chromatin condenses into chromosomes (two sister chromatids + centromere); nucleolus and nuclear membrane vanish; centrosomes move to poles; spindle forms. Metaphase: chromosomes maximally condensed, lined at the equator (metaphase plate); spindle fibres attach to centromeres; centromeres divide.

  • Easy : Best phase to count chromosomes = metaphase.
  • Medium : The nucleolus disappears in prophase.
  • Exam-type (CET) : Metaphase plate = line of chromosomes at the equator.
Remember

Prophase = condense + envelope vanishes; metaphase = line at equator.

Common mistake and CET trap

‘Chromatids go to poles in metaphase’ is wrong (anaphase). Trap: ‘meiosis in haploid cells’ is wrong.

Shortcut

Memory clue : "PMAT: Prophase, Metaphase, Anaphase, Telophase (‘Please Make Another Twin’)".

Spot the difference

TypeResultExample
Amitosis2 unequalBacteria
Mitosis2 identicalSomatic cells
Meiosis4 haploidGerm cells

Practice questions

Easy
  1. 1Where does amitosis occur?
  2. 2Four stages of mitosis.
  3. 3What disappears in prophase?
Medium
  1. 4What is the metaphase plate?
  2. 5Best phase to count chromosomes?
  3. 6Spindle fibres attach to?
Challenging
  1. 7Why is mitosis equational?
  2. 8Prophase vs metaphase.
Show answers (try them yourself first)
  1. 1Bacteria, old cells, foetal membrane.
  2. 2Prophase, metaphase, anaphase, telophase.
  3. 3Nucleolus and nuclear membrane.
  4. 4Chromosomes arranged at the equator.
  5. 5Metaphase.
  6. 6Centromere (kinetochore).
  7. 7Chromosome number stays the same.
  8. 8Prophase: condensing, envelope vanishes; metaphase: lined at equator.

Anaphase, telophase, cytokinesis and significance of mitosis

From daily life

In tug-of-war two teams pull a rope apart; in anaphase spindle fibres pull the chromosomes to opposite poles.

Simple definition

Anaphase: sister chromatids separate and daughter chromosomes move to poles. Telophase: nuclei re-form. Cytokinesis: division of cytoplasm – cleavage furrow in animals, cell plate in plants.

Anaphase to cytokinesisAnaphaseTelophaseCytokinesischromatids separate to polestwo nuclei; nucleolus returnscytoplasm dividesAnimal cellcleavage furrow (pinch inward)Plant cellcell plate (centre outward) = middle lamellavs

In the figure : Anaphase, telophase and cytokinesis; animal vs plant cells.

Rule 1 : Anaphase and telophase — Anaphase: centromeres divide; chromatids = daughter chromosomes; kinetochore fibres contract and polar fibres elongate → banana-bunch look. Telophase: chromosomes uncoil; nucleolus and nuclear membrane reappear; spindle dissolves; two nuclei.

  • Easy : Anaphase = chromosomes to poles; telophase = nuclei form.
  • Medium : Telophase reverses prophase.
  • Exam-type (CET) : Result: 2 nuclei but still one cell.

Rule 2 : Cytokinesis and significance — Animals: cleavage furrow at the equator, contractile ring of microfilaments; perpendicular to spindle. Plants: wall is rigid, so a cell plate (Golgi vesicles) grows outward from the centre = middle lamella. Significance: constant chromosome number; growth; replacing old cells; asexual reproduction; nucleo-cytoplasmic ratio. Limitation: no variation.

  • Easy : Furrow pinches inward; cell plate grows outward.
  • Medium : Mitosis = growth + repair + asexual reproduction.
  • Exam-type (CET) : Mitosis does not create variation.
Remember

Anaphase = separate; telophase = nuclei; cytokinesis = cells separate; plants = cell plate.

Common mistake and CET trap

‘Plants form a cleavage furrow’ is wrong. Trap: ‘mitosis creates variation’ is wrong.

Shortcut

Memory clue : "Animal = Pinch; Plant = Plate".

Spot the difference

PointAnimalPlant
CytokinesisCleavage furrowCell plate
DirectionOutside inCentre outward
ReasonNo wallRigid wall

Practice questions

Easy
  1. 1What happens in anaphase?
  2. 2Two features of telophase.
  3. 3What is cytokinesis?
Medium
  1. 4What forms the cell plate?
  2. 5Why no furrow in plants?
  3. 6Three significances of mitosis.
Challenging
  1. 7Limitation of mitosis?
  2. 8Kinetochore vs polar fibres.
Show answers (try them yourself first)
  1. 1Sister chromatids separate and move to poles.
  2. 2Nucleolus and envelope return; spindle disappears.
  3. 3Division of cytoplasm.
  4. 4Golgi vesicles; becomes middle lamella.
  5. 5Rigid cell wall.
  6. 6Growth; repair; asexual reproduction.
  7. 7Does not create new gene combinations.
  8. 8Kinetochore fibres contract; polar fibres elongate.

Meiosis: overview and prophase I

From daily life

A child gets half its chromosomes from each parent, so germ cells must first halve their chromosomes – the job of meiosis.

Simple definition

Meiosis (J. B. Farmer, 1905) = reductional division in germ cells; one diploid cell → four haploid cells. Two parts: Meiosis I (heterotypic) and Meiosis II (homotypic).

Meiosis outline and prophase IMeiosis: two divisions, four haploid cells2n → n + nMeiosis In,n → 4 × nMeiosis IIheterotypic/ homotypicProphase ILeptotenebouquetZygotenesynapsisPachytenecrossing overDiplotenechiasmataDiakinesisterminalisationHomologous chromosomes: one maternal + one paternalCrossing over = segment exchange between non-sister chromatids (recombination)Term meiosis: J. B. Farmer, 1905; meiocytes = dividing cellsProphase I is the longest; order L-Z-P-D-D

In the figure : Outline of meiosis and the five substages of prophase I.

Live figure

Meiosis: overview and prophase I

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Rule 1 : Outline of meiosis I — Meiosis I = diploid cell → two haploid cells (chromosome number halved). Stages: prophase I, metaphase I, anaphase I, telophase I, cytokinesis I. Prophase I is the longest and holds the special features of meiosis.

  • Easy : Meiocytes = cells that undergo meiosis.
  • Medium : Meiosis I is heterotypic – the type changes (2n → n).
  • Exam-type (CET) : Meiosis occurs only in reproductive cells.

Rule 2 : Five substages of prophase I — Leptotene: long thread-like chromosomes; bouquet. Zygotene: homologues pair – synapsis (synaptonemal complex). Pachytene: tetrads (4 chromatids); crossing over (between non-sister chromatids). Diplotene: chiasmata visible; desynapsis. Diakinesis: terminalisation; nucleolus and envelope vanish.

  • Easy : LZPDD = Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis.
  • Medium : Crossing over = pachytene; chiasmata visible = diplotene.
  • Exam-type (CET) : Synapsis = zygotene.
Remember

Synapsis (zygotene), crossing over (pachytene), chiasmata visible (diplotene), terminalisation (diakinesis).

Common mistake and CET trap

‘Crossing over in zygotene’ is wrong (pachytene). Trap: ‘meiosis in somatic cells’ is wrong.

Shortcut

Memory clue : "Lazy Zebras Play Dodge-ball Daily: L Z P D D".

Spot the difference

SubstageKey event
LeptoteneBouquet
ZygoteneSynapsis
PachyteneCrossing over, tetrad
DiploteneChiasmata, desynapsis

Practice questions

Easy
  1. 1Who coined meiosis?
  2. 2Result of meiosis?
  3. 3Five substages of prophase I.
Medium
  1. 4What is synapsis?
  2. 5When and between which?
  3. 6What are chiasmata?
Challenging
  1. 7Which is the bouquet stage?
  2. 8Why is meiosis I heterotypic?
Show answers (try them yourself first)
  1. 1J. B. Farmer (1905).
  2. 21 diploid → 4 haploid.
  3. 3Leptotene, zygotene, pachytene, diplotene, diakinesis.
  4. 4Pairing of homologous chromosomes.
  5. 5Pachytene; non-sister chromatids.
  6. 6X-shaped points of crossing over.
  7. 7Leptotene.
  8. 82n → n; chromosome number changes.

Metaphase I to meiosis II

From daily life

A bag of balls is split into two groups, then each is split again – four small groups in two rounds; so too meiosis.

Simple definition

Meiosis I: metaphase I (tetrads at equator), anaphase I (homologues separate – disjunction), telophase I. Meiosis II: mitosis-like; sister chromatids separate; four haploid cells.

Late meiosis I and meiosis IIMiddle and final stages of Meiosis IMetaphase IAnaphase ITelophase Itetrads at equatorhomologues separate (disjunction)2 haploid cells (interkinesis)Meiosis II (mitosis-like) → 4 haploid cellsProphase IIMetaphase IIAnaphase IITelophase IIMeiosis I = reductional | II = equational; sister chromatids split in II

In the figure : Metaphase–anaphase–telophase of meiosis I and the four phases of meiosis II.

Rule 1 : Rest of meiosis I — Metaphase I: tetrads at the equator; centromeres towards poles, arms towards equator. Anaphase I: homologous chromosomes separate (disjunction); sister chromatids do not separate. Telophase I: haploid sets at poles; two nuclei. Cytokinesis I: two haploid cells; a short interkinesis (sometimes absent).

  • Easy : Anaphase I = homologues separate; anaphase II = chromatids separate.
  • Medium : No DNA replication in interkinesis.
  • Exam-type (CET) : Recombination makes sister chromatids genetically different.

Rule 2 : Meiosis II — The two haploid cells divide again (mitosis-like; homotypic). Prophase II: chromosomes visible; centrioles to poles. Metaphase II: at equator; centromeres divide. Anaphase II: sister chromatids to poles. Telophase II + cytokinesis II: four haploid cells in all → gametes.

  • Easy : Meiosis II = equational.
  • Medium : One meiocyte gives 4 cells; 80 sperms = 20 meiocytes.
  • Exam-type (CET) : Chromosome number does not change in meiosis II.
Remember

Anaphase I = homologues; anaphase II = sister chromatids; finally 4 haploid cells.

Common mistake and CET trap

‘Chromatids separate in anaphase I’ is wrong. Trap: ‘meiosis II is reductional’ is wrong (equational).

Shortcut

Memory clue : "I = Homologues part; II = Chromatids part".

Spot the difference

PointMeiosis IMeiosis II
SeparatesHomologuesSister chromatids
TypeReductionalEquational
Result2 haploid4 haploid

Practice questions

Easy
  1. 1Chromosomes in metaphase I?
  2. 2What is disjunction?
  3. 3What does not separate in anaphase I?
Medium
  1. 4What is interkinesis?
  2. 5Why is meiosis II homotypic?
  3. 6How many meiocytes for 80 sperms?
Challenging
  1. 7Chromatids in anaphase I of 2n = 20?
  2. 8Two differences between meiosis I and II.
Show answers (try them yourself first)
  1. 1Tetrads at the equator.
  2. 2Separation of homologous chromosomes.
  3. 3Sister chromatids.
  4. 4Short pause between meiosis I and II.
  5. 5Chromosome number same; mitosis-like.
  6. 620.
  7. 740.
  8. 8Homologues / sister chromatids separate; reductional / equational.

Significance of meiosis and mitosis versus meiosis

From daily life

Siblings from the same parents differ because meiosis shuffles chromosomes into new mixtures each time.

Simple definition

Significance of meiosis: forms gametes/spores; keeps chromosome number constant across generations; crossing over gives variation (raw material for evolution). Mitosis = 2 identical cells; meiosis = 4 different haploid cells.

Mitosis vs meiosisMitosisMeiosis2n2n2n1 division → 2 identical cells2nnnnnnn2 divisions → 4 haploid cellsWheresomatic cellsgerm cellsVariationnonecrossing over → variationRolegrowth, repairgametes/sporesMitosis = equational | Meiosis I = reductional

In the figure : Mitosis vs meiosis: number of cells and chromosome sets.

Rule 1 : Significance of meiosis — Without meiosis the chromosome number would double each generation, causing abnormalities. Meiosis + fertilisation keep a species' number constant. Crossing over and independent assortment of homologues → genetic variation → evolution.

  • Easy : Meiosis: 2n → n; fertilisation: n + n → 2n.
  • Medium : Variation = raw material of evolution.
  • Exam-type (CET) : Meiosis aids evolution (new gene combinations).

Rule 2 : Mitosis vs Meiosis — Mitosis: somatic cells; one division; 2 cells, 2n; same number (equational); no crossing over; growth/repair. Meiosis: germ cells; two divisions; 4 cells, n; halved number (reductional); synapsis + crossing over; variation.

  • Easy : Synapsis and chiasmata occur only in meiosis.
  • Medium : Mitosis daughters are identical to the parent.
  • Exam-type (CET) : Meiosis I = reductional; meiosis II = equational.
Remember

Mitosis 2 × 2n identical; meiosis 4 × n different; crossing over only in meiosis.

Common mistake and CET trap

‘Meiosis causes growth’ is wrong. Trap: ‘synapsis in mitosis’ is wrong.

Shortcut

Memory clue : "Mitosis = Make Identical Twins; Meiosis = Makes gametes + Variety".

Spot the difference

PointMitosisMeiosis
Cells2 (2n)4 (n)
Crossing overNoYes
RoleGrowth, repairGametes, variation

Practice questions

Easy
  1. 1Two significances of meiosis.
  2. 2What if there were no meiosis?
  3. 3How many cells does mitosis form?
Medium
  1. 4And meiosis?
  2. 5Why is crossing over important?
  3. 6Onion leaf cell has 16; root and pollen?
Challenging
  1. 7Three differences of mitosis and meiosis.
  2. 8How does meiosis cause evolution?
Show answers (try them yourself first)
  1. 1Constant chromosome number; variation.
  2. 2Chromosome number would double each generation causing abnormalities.
  3. 32.
  4. 44 haploid.
  5. 5Genetic variation.
  6. 6Root 16; pollen 8.
  7. 7Cells 2/4; 2n/n; no/yes crossing over.
  8. 8Creates variation that natural selection acts on.

Cell cycle control, cell death and applied counts

From daily life

Like traffic signals, the cell cycle has checkpoints; if they fail, cells grow out of control – cancer.

Simple definition

Cell cycle control: cyclins, CDKs (cyclin-dependent kinases) and MPF. Necrosis = cell death by injury; apoptosis = programmed cell death (‘cellular suicide’).

Control, cell death and countsControl of the cell cycleG1 → SG2 → MMetaphasecheckpointsCyclins + CDKs (kinases) + MPF decide the next phaseLost control → uncontrolled division = cancerNecrosis: injury kills cellApoptosis: programmed death≠e.g. cells between embryonic fingersCounts: 2n = 16 (onion)root cell 16 | pollen 8 | each meiotic product 880 sperms → 20 meiocytes (4 each)2n = 20: anaphase I has 40 chromatids, 20 chromosomes

In the figure : Checkpoints, necrosis vs apoptosis and chromosome-count examples.

Rule 1 : Control and cell death — Cyclins, MPF (maturation promoting factor) and CDKs drive the cycle forward; checkpoints at G1/S, G2/M and metaphase. Loss of control causes cancer. Necrosis: caused by injury/chemical; apoptosis: cells between embryonic fingers die; cancer cells eliminated.

  • Easy : Apoptosis benefits the organism; necrosis harms it.
  • Medium : Cyclin = cycle signal; CDK = kinase enzyme.
  • Exam-type (CET) : Cancer = failure of cell-cycle control.

Rule 2 : Chromosome and cell-count problems — Rules: mitosis keeps 2n; meiosis gives n; cells: mitosis ×2, meiosis ×4. E.g. onion 2n = 16: root 16, pollen 8. 80 sperms → 20 meiocytes. 2n = 20: anaphase I has 40 chromatids, 20 chromosomes; anaphase II has 20 chromosomes in each cell (40 in the two cells together).

  • Easy : Chromatids = chromosomes × 2 after S-phase.
  • Medium : Sperms ÷ 4 = meiocytes.
  • Exam-type (CET) : In anaphase II chromatids become independent chromosomes.
Remember

Control: cyclin-CDK-MPF; apoptosis = programmed; meiocytes = sperms ÷ 4.

Common mistake and CET trap

‘Necrosis is programmed’ is wrong. Trap: ‘chromatids separate in anaphase I’ is wrong.

Shortcut

Memory clue : "Necro = Nasty (injury); Apo = Appointed (planned)".

Spot the difference

PointNecrosisApoptosis
CauseInjuryProgrammed signal
EffectHarmUseful

Practice questions

Easy
  1. 1Expand MPF.
  2. 2What is a checkpoint?
  3. 3Example of apoptosis.
Medium
  1. 4Necrosis vs apoptosis.
  2. 5Onion 2n = 16; chromosomes in pollen?
  3. 6Meiocytes for 80 sperms?
Challenging
  1. 7Chromatids in anaphase I if 2n = 20?
  2. 8Why does cancer arise?
Show answers (try them yourself first)
  1. 1Maturation promoting factor.
  2. 2A control point in the cell cycle.
  3. 3Death of cells between embryonic fingers.
  4. 4By injury / programmed; harmful / useful.
  5. 58.
  6. 620.
  7. 740.
  8. 8Loss of cell-cycle control causes uncontrolled division.

Quick revision of the whole lesson

ConceptKey fact
Cell cycleG1 → S (DNA) → G2 → M; interphase longest
MitosisPMAT; equational; 2 × 2n
CytokinesisAnimal: furrow; plant: cell plate
Prophase IL-Z-P-D-D; synapsis; crossing over
Meiosis I / IIHomologues / chromatids separate; 4 × n
SignificanceConstant number; variation; evolution
Death / countsNecrosis vs apoptosis; 80 sperms = 20 meiocytes

🎯 Most important points for the exam

  • Functions of G1, S, G2, M.
  • Mitosis stages and animal/plant cytokinesis.
  • Substages of prophase I and crossing over.
  • Differences of meiosis I and II.
  • Mitosis vs meiosis table.
  • Chromosome / chromatid / cell-count problems.
Study mantra

Understand the concept → draw the figure → memorise the key points → solve questions yourself.