Cell Cycle and Cell Division (NCERT Practice Paper)
Q1. The term 'equational division' is applied to:
Correct Answer: (d)
Both mitosis and meiosis II are equational because the chromosome number remains unchanged after division. In mitosis, diploid → diploid; in meiosis II, haploid → haploid (after reduction in meiosis I). Meiosis I is reductional.
Q2. Assertion: In S phase, the chromosome number per cell doubles.
Reason: DNA replication takes place during S phase.
Correct Answer: (d)
The assertion is false: chromosome number does not double during S phase; only the DNA content doubles. The reason is true (DNA replication occurs in S phase). Therefore, assertion is false, but reason is true.
Q3. Which statements about Cytokinesis are correct? (i) In animals, it occurs by a furrow in the plasma membrane. (ii) In plants, it starts in the centre and grows outward. (iii) Cell plate represents the middle lamella.
Correct Answer: (c)
Animal cytokinesis uses a cleavage furrow (i). Plant cytokinesis forms a cell plate that grows centrifugally (ii). The cell plate becomes the middle lamella (iii). All correct.
Q4. Nuclear envelope and nucleolus disappear during:
Correct Answer: (a)
By late prophase, the nuclear envelope breaks down and the nucleolus disintegrates. This allows the spindle apparatus to interact with chromosomes. The nuclear envelope reforms during telophase.
Q5. Assertion: In animal cells, the centrioles move towards opposite poles during prophase.
Reason: Centrioles undergo duplication during the G2 phase.
Correct Answer: (c)
The assertion is true: centrioles migrate to poles during prophase. But the reason is false because centrioles duplicate during S phase, not G2. Thus, assertion true, reason false.
Q6. Which statements about the G0 stage are correct? (i) Cells remain metabolically active. (ii) Cells no longer proliferate unless called upon. (iii) Heart cells are an example of cells that do not divide often.
Correct Answer: (c)
G0 cells are metabolically active (i). They do not proliferate unless stimulated (ii). Heart cells are often in G0 (iii). All statements are correct.
Q7. Centriole duplication in animal cells occurs during:
Correct Answer: (c)
Centrioles duplicate in the cytoplasm during the S phase, along with DNA replication. This ensures that each daughter cell receives a centrosome during mitosis. Centriole duplication is not a feature of plant cells, which lack centrioles.
Q8. The sequence of events by which a cell duplicates its genome and eventually divides into two daughter cells is termed:
Correct Answer: (b)
The cell cycle is the ordered series of events that lead to cell duplication and division. It includes interphase (preparation) and M phase (division). Generation time is the duration of the entire cycle, not the sequence itself.
Q9. Assertion: Crossing over is important for evolution.
Reason: It produces new combinations of genes and increases genetic variability.
Correct Answer: (a)
Crossing over creates new allelic combinations, which are a source of genetic variation. This variation is essential for evolution by natural selection. Thus, the reason correctly explains the evolutionary importance of crossing over.
Q10. Match the following for Prophase I phases based on sequence:
Order
Phase
1st
Leptotene
2nd
Zygotene
3rd
Pachytene
4th
Diplotene
5th
Diakinesis
Correct Answer: (a)
The correct order of prophase I sub‑stages is: Leptotene → Zygotene → Pachytene → Diplotene → Diakinesis. The given sequence matches this order exactly. Thus, it is correct.
Q11. Regarding Prophase I, which are correct? (i) It is typically longer and more complex than prophase of mitosis. (ii) It is divided into five phases based on chromosomal behaviour. (iii) Zygotene involves the formation of the synaptonemal complex.
Correct Answer: (c)
Prophase I is long and complex (i). It has five sub‑stages (ii). Zygotene includes synaptonemal complex formation (iii). All are correct.
Q12. Meiosis results in the formation of how many haploid cells?
Correct Answer: (c)
Meiosis produces four haploid daughter cells from one diploid parent cell. Each of the four cells has half the chromosome number (n) and is genetically distinct. These cells are gametes or spores.
Q13. Regarding Mitosis in plants, which are true? (i) Occurs in both haploid and diploid cells. (ii) Apical and lateral cambium show mitotic divisions. (iii) Leads to continuous growth throughout life.
Correct Answer: (c)
Mitosis occurs in haploid (gametophytes) and diploid (sporophytes) plant cells (i). Cambium tissues divide mitotically (ii). Plants grow continuously due to meristems (iii). All correct.
Q14. Centrosome duplication in interphase happens during:
Correct Answer: (b)
The centrosome (containing centrioles in animal cells) duplicates during S phase. This ensures that each daughter cell receives one centrosome to organise spindle fibres. Centrosome duplication is coordinated with DNA replication.
Q15. The complex formed by a pair of synapsed homologous chromosomes is called:
Correct Answer: (b)
A bivalent (or tetrad) is the structure formed by two homologous chromosomes during synapsis. It comprises four chromatids (two from each homologue). Bivalents are visible during prophase I and metaphase I.
Q16. X-shaped structures observed during Diplotene are called:
Correct Answer: (b)
Chiasmata are the X‑shaped junctions where crossing over has occurred. They represent the physical manifestation of genetic recombination. Chiasmata hold homologous chromosomes together until anaphase I.
Q17. Meiosis I is initiated after the parental chromosomes have replicated to produce identical sister chromatids at:
Correct Answer: (c)
DNA replication occurs during the S phase of interphase, preceding meiosis. Thus, at the start of meiosis I, each chromosome consists of two sister chromatids. This is necessary for crossing over and proper segregation.
Q18. Cells that do not divide further exit G1 phase to enter an inactive stage called:
Correct Answer: (d)
Cells that are not destined to divide enter a resting state known as G0 phase. In G0, cells remain metabolically active but do not proliferate unless stimulated. Examples include neurons, heart cells, and differentiated cells that rarely divide.
Q19. Small disc-shaped structures at the surface of centromeres are called:
Correct Answer: (c)
Kinetochores are proteinaceous discs that assemble on the centromere region. They serve as attachment points for spindle microtubules during chromosome movement. Without kinetochores, proper segregation during mitosis/meiosis would fail.
Q20. If a cell has 2C amount of DNA at G1, what will be the DNA content after S phase?
Correct Answer: (c)
During S phase, the entire genome is replicated, so the DNA content doubles from 2C to 4C. The 'C' value represents the haploid DNA content. Chromosome number (2n) remains unchanged despite the doubling of DNA.
Q21. Match the following cell types with their division patterns:
Column I
Column II
A. Diploid somatic cells
(I) Mitosis in animals
B. Male honey bees
(II) Haploid mitosis
C. Specialized diploid cells
(III) Meiosis
Correct Answer: (a)
Diploid somatic cells undergo mitosis (I). Male honey bees are haploid and divide by mitosis (II). Specialized diploid cells produce gametes by meiosis (III). So A–I, B–II, C–III.
Q22. Identify the correct features of Telophase: (i) Chromosomes decondense and lose their individuality. (ii) Nuclear envelope develops around chromosome clusters. (iii) Nucleolus and Golgi reform.
Correct Answer: (c)
In telophase, chromosomes decondense (i). Nuclear envelope re‑forms (ii). Nucleolus and Golgi reappear (iii). All are true.
Q23. Identify the stage: (i) Chromosomes move to opposite poles. (ii) Centromere splitting does not occur. (iii) Sister chromatids stay together.
Correct Answer: (b)
In Anaphase I of meiosis, homologous chromosomes move to poles, but sister chromatids remain joined. Centromeres do not split. This distinguishes it from mitotic anaphase and anaphase II.
Q24. During which phase is the cell metabolically active and continuously growing but does not replicate DNA?
Correct Answer: (b)
G1 phase is a period of intense metabolic activity and cell growth. DNA replication does not occur in G1; that happens in the subsequent S phase. Cells may also enter G0 from G1 if they are not dividing.
Q25. Chromosomes move to opposite poles during Anaphase by the shortening of:
Correct Answer: (c)
Anaphase movement is powered by the shortening of kinetochore microtubules. These microtubules pull chromosomes towards the poles by depolymerising at the kinetochore ends. This is a dynamic process involving motor proteins.
Q26. Which of the following is correct? (i) Antonie Von Leeuwenhoek first saw a live cell. (ii) Robert Brown discovered the nucleus. (iii) Every chromosome has a centromere.
Correct Answer: (c)
Leeuwenhoek observed live cells (i). Brown identified the nucleus (ii). All chromosomes possess a centromere (iii). Thus, all statements are correct.
Q27. Assertion: The interphase is called the resting phase.
Reason: It is the time during which the cell is preparing for division by undergoing cell growth and DNA replication.
Correct Answer: (a)
Interphase is historically termed 'resting', but it is actually a period of intense activity. The reason accurately describes the preparatory events (growth and DNA replication). Thus, both statements are true, and the reason correctly explains why it is called resting (though it's a misnomer).
Q28. In oocytes of some vertebrates, which stage can last for months or years?
Correct Answer: (c)
Diplotene can be prolonged for months or years in vertebrate oocytes. During this extended stage, the oocyte grows and accumulates nutrients. This arrested stage allows the oocyte to complete meiosis later upon hormonal stimulation.
Q29. Match the following for plant growth:
Column I
Column II
A. Meristematic tissues
(I) Continuous growth in plants
B. Apical cambium
(II) Mitotic division location
C. Lateral cambium
(III) Mitotic division location
Correct Answer: (a)
Meristematic tissues are responsible for continuous growth (I). Both apical and lateral cambium are sites of mitotic divisions (II and III). Thus, A–I, B–II, C–III.
Q30. In plant cells, the precursor of the cell wall is called:
Correct Answer: (a)
In plant cells, vesicles from the Golgi fuse to form a cell plate at the equator. This plate grows outward and becomes the middle lamella and eventually the cell wall. This is a unique mechanism because plant cells are enclosed by a rigid wall and cannot form a furrow.
Q31. The production of haploid daughter cells from specialized diploid cells is achieved by:
Correct Answer: (b)
Meiosis is the specialized division that reduces the chromosome number from diploid (2n) to haploid (n). It involves two rounds of division (Meiosis I and II) and is essential for sexual reproduction. It produces gametes or spores.
Q32. Which organelle is distributed between daughter cells during cytokinesis?
Correct Answer: (c)
During cytokinesis, cytoplasmic organelles such as mitochondria and plastids are partitioned between daughter cells. These organelles are not synthesised de novo but are inherited through division. Their distribution is roughly equal, though not always exact.
Q33. The enzyme involved in crossing over is called:
Correct Answer: (c)
Recombinase is the key enzyme that mediates strand exchange during crossing over. It facilitates the breakage and rejoining of DNA molecules between non‑sister chromatids. This process increases genetic diversity.
Q34. The stage of mitosis where chromosomes are most easily studied under the microscope is:
Correct Answer: (b)
During metaphase, chromosomes are maximally condensed and aligned at the equatorial plate. This makes their morphology, including centromere position, most visible and distinct. Karyotyping is typically performed on metaphase chromosomes.
Q35. Identify the correct phylum/group being described: (i) These cells enter an inactive stage (G0). (ii) They remain metabolically active. (iii) Example: Heart cells.
Correct Answer: (a)
The description matches cells in G0 (quiescent stage). They are metabolically active but do not divide. Heart cells are a classic example of G0 cells.
Q36. Identify the features of Meiosis: (i) Two sequential cycles of nuclear division (Meiosis I and II). (ii) Only a single cycle of DNA replication. (iii) Homologous chromosomes pair and recombine.
Correct Answer: (c)
Meiosis has two divisions (I and II) (i). It involves one round of DNA replication (ii). Homologous chromosomes synapse and undergo crossing over (iii). All correct.
Q37. The reform of nucleolus, Golgi complex, and ER occurs in:
Correct Answer: (d)
Telophase is the reverse of prophase: the nuclear envelope reforms, chromosomes decondense, and organelles like nucleolus and Golgi reappear. This re‑establishes the interphase state in each daughter nucleus. It prepares the cell for cytokinesis.
Q38. Match the chromosome type with centromere position:
Column I
Column II
A. Metacentric
(I) Centromere close to one end
B. Sub-metacentric
(II) Middle centromere
C. Acrocentric
(III) Terminal centromere
D. Telocentric
(IV) Slightly away from middle
Correct Answer: (a)
Metacentric has centromere in the middle (II). Sub‑metacentric has centromere slightly off‑centre (IV). Acrocentric has centromere near one end (I). Telocentric has centromere at the terminal end (III). Thus, A–II, B–IV, C–I, D–III.
Q39. Which of the following describes the 'Dyad of cells'? (i) Formed at the end of Telophase I. (ii) Consists of two cells. (iii) Nuclear membrane and nucleolus reappear.
Correct Answer: (c)
At the end of Telophase I, two cells are formed (dyad) (i and ii). Nuclear membrane and nucleolus re‑form in Telophase I (iii). All correct.
Q40. Crossing over between non-sister chromatids occurs during:
Correct Answer: (b)
Pachytene is the stage where crossing over (genetic recombination) occurs. Enzymes like recombinase facilitate the exchange of segments between non‑sister chromatids of homologous chromosomes. This leads to new combinations of alleles.
Q41. Assertion: Diakinesis represents transition to metaphase.
Reason: By the end of diakinesis, the nuclear envelope breaks down.
Correct Answer: (a)
Diakinesis is the final stage of prophase I and leads directly into metaphase I. The nuclear envelope breaks down at the end of diakinesis, allowing spindle attachment. Thus, the reason correctly explains why it is a transition phase.
Q42. The interphase lasts for more than ____ of the total duration of the cell cycle.
Correct Answer: (d)
Interphase is the longest phase, occupying more than 95% of the cell cycle. This is because the cell must grow, replicate DNA, and prepare for division. M phase, including mitosis and cytokinesis, is relatively short.
Q43. Which statements about Anaphase are correct? (i) Centromeres split simultaneously. (ii) Chromatids move to opposite poles. (iii) Centromere of each chromosome remains directed towards the pole.
Correct Answer: (c)
Centromeres divide at anaphase (i). Sister chromatids (now chromosomes) move to poles (ii). Centromeres lead the way towards the poles (iii). All statements are correct.
Q44. In animal cells, cytokinesis is achieved by the appearance of a ______ in the plasma membrane.
Correct Answer: (b)
Animal cells divide by a process called cleavage, where a furrow ingresses from the periphery. The furrow deepens and pinches the cell into two daughter cells. This is possible because animal cells lack a rigid cell wall.
Q45. Which process increases genetic variability in the population from one generation to the next?
Correct Answer: (b)
Meiosis increases genetic variability through crossing over and independent assortment of chromosomes. These mechanisms create new combinations of alleles. Such variation is the raw material for evolution and natural selection.
Q46. Which statements about Diplotene are correct? (i) Dissolution of the synaptonemal complex. (ii) Homologous chromosomes tend to separate. (iii) Formation of X-shaped chiasmata.
Correct Answer: (c)
Diplotene: synaptonemal complex dissolves (i). Homologous chromosomes begin to separate (ii). Chiasmata become visible (iii). All correct.
Q47. Match the mitosis phase with its key feature:
Column I
Column II
A. Prophase
(I) Centromeres split
B. Metaphase
(II) Chromosomes decondense
C. Anaphase
(III) Initiation of condensation
D. Telophase
(IV) Alignment at equator
Correct Answer: (a)
Prophase: chromosomal material condenses (III). Metaphase: chromosomes align at the equatorial plate (IV). Anaphase: centromeres split and chromatids separate (I). Telophase: chromosomes decondense (II). Thus, A–III, B–IV, C–I, D–II.
Q48. Assertion: Interkinesis is a short-lived stage between Meiosis I and II.
Reason: There is no replication of DNA during interkinesis.
Correct Answer: (b)
Both statements are true: interkinesis is short, and no DNA replication occurs. However, the lack of DNA replication is not the cause of its short duration; it is simply a gap phase. Thus, reason is true but does not explain the shortness.
Q49. Assertion: Crossing over occurs between homologous chromosomes.
Reason: It occurs between sister chromatids of a bivalent.
Correct Answer: (c)
The assertion is true: crossing over involves homologous chromosomes. But the reason is false because crossing over occurs between non‑sister chromatids, not sister chromatids. Thus, assertion true, reason false.
Q50. Assertion: Cell division does not stop with the formation of the mature organism.
Reason: Cells are constantly being replaced for repair and growth.
Correct Answer: (a)
The assertion is true because even in adults, cell division occurs to replace worn‑out cells. The reason correctly explains this: repair (e.g., wound healing) and growth (e.g., hair, nails, blood cells) require ongoing mitosis. Thus, the reason is the correct explanation for the assertion.
Q51. Select correct statements about chromosomes in Metaphase I: (i) Bivalent chromosomes align on the equatorial plate. (ii) Microtubules from opposite poles attach to homologous chromosomes. (iii) Sister chromatids separate during this stage.
Correct Answer: (a)
In Metaphase I, bivalents align at the equator (i). Spindle fibres attach to homologous chromosomes (ii). Sister chromatids do NOT separate in Metaphase I; they separate in Anaphase II (iii). Thus, only (i) and (ii) are correct.
Q52. Match the stages of Prophase I with characteristic events:
Column I
Column II
A. Zygotene
(I) Crossing over
B. Pachytene
(II) Synapsis
C. Diplotene
(III) Terminalisation of chiasmata
D. Diakinesis
(IV) Chiasmata formation
Correct Answer: (a)
Zygotene is characterised by synapsis (II). Pachytene is the stage of crossing over (I). Diplotene shows chiasmata formation (IV). Diakinesis is marked by terminalisation of chiasmata (III). So A–II, B–I, C–IV, D–III.
Q53. Match the following significance:
Column I
Column II
A. Mitosis
(I) Conservation of chromosome number
B. Meiosis
(II) Production of diploid daughter cells
C. Crossing over
(III) Cell repair
D. Mitosis
(IV) Genetic variability
Correct Answer: (a)
Mitosis produces diploid daughter cells (II) and aids in cell repair (III). Meiosis conserves chromosome number across generations by halving and then restoring via fertilisation (I). Crossing over generates genetic variability (IV). Thus, A–II, B–I, C–IV, D–III.
Q54. Assertion: Mitosis is called equational division.
Reason: The number of chromosomes in parent and progeny cells is the same.
Correct Answer: (a)
The assertion is correct: mitosis maintains chromosome number. The reason provides the direct explanation: parent and daughter cells have the same chromosome count (2n). Thus, both are true and the reason correctly explains the assertion.
Q55. A cell in G0 phase is:
Correct Answer: (b)
Cells in G0 are metabolically active but have withdrawn from the cell cycle and do not divide. They may re‑enter the cycle if stimulated (e.g., liver cells). Examples include fully differentiated cells like neurons and muscle cells.
Q56. Identify the correct events of Prophase: (i) Initiation of condensation of chromosomal material. (ii) Centrosome begins to move towards opposite poles. (iii) Nuclear envelope disintegrates.
Correct Answer: (c)
Prophase includes chromosome condensation (i). Centrosomes migrate to opposite poles (ii). The nuclear envelope breaks down by late prophase (iii). All are correct.
Q57. Correct statements about the cell cycle: (i) Cells vary in their shape and size. (ii) All cells start their life from a single cell. (iii) Cycles of growth and division allow one cell to form millions of cells.
Correct Answer: (c)
Cells are diverse in shape and size (i). All cells originate from a single cell (zygote) (ii). Repeated cycles generate multicellular organisms (iii). All correct.
Q58. Match the phases of Meiosis II:
Column I
Column II
A. Metaphase II
(I) Tetrad of cells
B. Anaphase II
(II) Alignment at equator
C. Telophase II
(III) Splitting of centromere
Correct Answer: (a)
Metaphase II: chromosomes align at equator (II). Anaphase II: centromeres split (III). Telophase II results in four cells (tetrad) (I). So A–II, B–III, C–I.
Q59. Assertion: Synapsis occurs during the zygotene stage of Prophase I.
Reason: It involves the pairing of homologous chromosomes.
Correct Answer: (a)
Synapsis is the pairing of homologous chromosomes, which indeed occurs during zygotene. The reason defines synapsis correctly. Hence, the reason is the correct explanation for the assertion.
Q60. Significance of Mitosis includes: (i) Production of diploid daughter cells with identical genetic complement. (ii) Growth of multicellular organisms. (iii) Cell repair and replacement of blood cells.
Correct Answer: (c)
Mitosis produces genetically identical diploid cells (i). It is essential for organismal growth (ii). It replaces damaged cells, e.g., blood cells (iii). All are correct.
Q61. Match the sub-phases of Interphase with their descriptions:
Column I
Column II
A. G1 phase
(I) DNA replication
B. S phase
(II) Centriole duplication in cytoplasm
C. G2 phase
(III) Metabolically active, no DNA replication
D. S phase (animal)
(IV) Protein synthesis for mitosis
Correct Answer: (a)
G1 phase is metabolically active with no DNA replication (III). S phase is dedicated to DNA replication (I). G2 phase involves protein synthesis and preparation for mitosis (IV). In animal cells, centriole duplication occurs during S phase (II). Thus, A–III, B–I, C–IV, D–II is correct.
Q62. Assertion: Adult human haemoglobin consists of 4 subunits.
Reason: Mitosis produces daughter cells with identical genetic complements.
Correct Answer: (b)
Both statements are true, but they are unrelated facts. The haemoglobin structure does not explain mitosis, nor vice versa. Thus, both true but reason is not a correct explanation.
Q63. Terminalisation of chiasmata occurs during:
Correct Answer: (c)
Diakinesis is the final stage of prophase I, marked by the terminalisation (movement to the ends) of chiasmata. This ensures that homologous chromosomes are ready to separate in anaphase I. The nuclear envelope breaks down by the end of diakinesis.
Q64. In the cell cycle, DNA synthesis occurs during:
Correct Answer: (c)
The S (synthesis) phase is specifically dedicated to DNA replication. During this phase, the amount of DNA per cell doubles while chromosome number remains unchanged. G1 and G2 are growth phases, and M phase is division.
Q65. Multinucleate condition arising when karyokinesis is not followed by cytokinesis is called:
Correct Answer: (c)
A syncytium is a cell containing multiple nuclei within a common cytoplasm. This occurs when nuclear division (karyokinesis) occurs without cytoplasmic division (cytokinesis). Examples include liquid endosperm in plants and some muscle cells.
Q66. Match the following for cytokinesis:
Column I
Column II
A. Animal cell
(I) Cell plate formation
B. Plant cell
(II) Furrow appearance
C. Liquid endosperm
(III) Middle lamella precursor
D. Cell plate
(IV) Syncytium example
Correct Answer: (a)
Animal cells: furrow formation (II). Plant cells: cell plate formation (I). Liquid endosperm: example of a syncytium (IV). Cell plate is the precursor of the middle lamella (III). So A–II, B–I, C–IV, D–III.
Q67. Regarding S phase, which statements are true? (i) DNA amount doubles. (ii) Chromosome number remains the same. (iii) Centriole duplicates in animal cells.
Correct Answer: (c)
In S phase, DNA content doubles (i). Chromosome number stays constant (ii). Centriole duplication occurs in animal cells during S phase (iii). Thus, all are correct.
Q68. Assertion: Plant cells undergo cytokinesis by a different mechanism than animal cells.
Reason: Plant cells are enclosed by a relatively inextensible cell wall.
Correct Answer: (a)
Plant cells cannot form a cleavage furrow because of their rigid cell wall. Instead, they form a cell plate by vesicle fusion. Thus, the reason correctly explains the different mechanism.
Q69. Assertion: Mitosis helps in cell repair.
Reason: Cells of the upper layer of epidermis and lining of the gut are constantly being replaced.
Correct Answer: (a)
Mitosis is essential for replacing damaged or dead cells. The reason gives specific examples (epidermis, gut lining) where rapid cell replacement occurs. Thus, the reason correctly explains why mitosis is important for repair.
Q70. Assertion: Meiosis maintains the specific chromosome number of each species across generations.
Reason: It involves two sequential cycles of DNA replication.
Correct Answer: (c)
The assertion is true: meiosis halves the chromosome number, and fertilisation restores it, maintaining species constancy. But the reason is false because meiosis involves only one cycle of DNA replication (before meiosis I), not two. Thus, assertion true, reason false.
Q71. Assertion: Meiosis I is called reduction division.
Reason: It reduces the chromosome number by half.
Correct Answer: (a)
Meiosis I is indeed the reduction division because homologous chromosomes separate, halving the chromosome number from 2n to n. The reason directly explains this reduction. Thus, both are true and the reason is correct.
Q72. Assertion: The period between two successive M phases is called interphase.
Reason: Cell division proper lasts for only about an hour in a 24-hour cycle.
Correct Answer: (b)
Interphase is indeed the interval between M phases. It is true that M phase (division) is short relative to the total cycle. However, the short duration of M phase is not the definition of interphase; interphase is defined by its preparatory activities.
Q73. Which of the following statements about cell growth is correct? (i) Cell growth (cytoplasmic increase) is a continuous process. (ii) DNA synthesis occurs only during one specific stage. (iii) All cell cycle events are under genetic control.
Correct Answer: (c)
Cell growth is continuous throughout interphase (i). DNA synthesis is restricted to the S phase (ii). The cell cycle is regulated by genes and checkpoints (iii). Thus, all statements are correct.
Q74. Match the chromosomal structures:
Column I
Column II
A. Satellite
(I) Primary constriction
B. Centromere
(II) Held by centromere
C. Chromatids
(III) Secondary constriction
Correct Answer: (a)
Satellite is a secondary constriction (III). Centromere is the primary constriction (I). Chromatids are held together by the centromere (II). Thus, A–III, B–I, C–II.
Q75. Match the following for Cell Cycle duration:
Column I
Column II
A. Human cell cycle
(I) About 1 hour
B. M Phase (Human)
(II) Approximately 24 hours
C. Yeast cell cycle
(III) More than 95% of cycle
D. Interphase
(IV) About 90 minutes
Correct Answer: (a)
Human cell cycle: ~24 hours (II). Human M phase: ~1 hour (I). Yeast cell cycle: ~90 minutes (IV). Interphase occupies >95% of the cycle (III). Thus, A–II, B–I, C–IV, D–III.
Q76. Which phase is characterized by chromosomes moving to the spindle equator and aligning along the metaphase plate?
Correct Answer: (b)
Metaphase is defined by the alignment of chromosomes at the metaphase plate (equatorial plane). This ensures that each daughter cell receives an equal set of chromosomes. The spindle fibres attach to kinetochores and pull chromosomes into position.
Q77. A typical human cell in culture divides once in approximately every:
Correct Answer: (b)
Human cells in culture typically have a cell cycle duration of about 24 hours. This includes a long interphase (about 23 hours) and a short M phase (about 1 hour). Yeast cells divide much faster, in about 90 minutes.
Q78. Identify correct features of Meiosis II: (i) Resembles a normal mitosis. (ii) Initiated immediately after cytokinesis. (iii) Centromeres split during Anaphase II.
Correct Answer: (c)
Meiosis II is similar to mitosis (i). It starts after cytokinesis of meiosis I (ii). Centromeres split in Anaphase II (iii). All are true.
Q79. During S phase, if the initial chromosome number was 2n, the number of chromosomes after S phase will be:
Correct Answer: (c)
Replication of DNA during S phase does not increase the chromosome count. Each chromosome now consists of two sister chromatids joined at the centromere, but the number of chromosomes (centromeres) stays 2n. The chromosome number doubles only during anaphase (mitosis) or anaphase II (meiosis).
Q80. Match the terms with their definitions:
Column I
Column II
A. Karyokinesis
(I) Division of cytoplasm
B. Cytokinesis
(II) Pairing of homologous chromosomes
C. Synapsis
(III) Nuclear division
D. Crossing over
(IV) Exchange of genetic material
Correct Answer: (a)
Karyokinesis is nuclear division (III). Cytokinesis is cytoplasmic division (I). Synapsis is the pairing of homologous chromosomes (II). Crossing over involves exchange of genetic material (IV). So A–III, B–I, C–II, D–IV.
Q81. Assertion: The M phase starts with nuclear division (karyokinesis).
Reason: Karyokinesis corresponds to the separation of daughter chromosomes.
Correct Answer: (c)
The assertion is true: M phase begins with karyokinesis (nuclear division). However, the reason is false because karyokinesis is the entire process of nuclear division, not just the separation of daughter chromosomes (which is anaphase). Thus, assertion true, reason false.
Q82. Assertion: Small disc-shaped structures called kinetochores are present on the centromere.
Reason: Kinetochores serve as the sites of attachment of spindle fibres.
Correct Answer: (a)
Kinetochores are indeed protein discs at the centromere. Their main function is to attach to spindle microtubules for chromosome movement. Thus, the reason correctly explains the presence and role of kinetochores.
Q83. What is the duration of the cell cycle for Yeast?
Correct Answer: (c)
Yeast cells progress through the cell cycle rapidly, completing it in about 90 minutes. This short duration is characteristic of many unicellular organisms. Human cells, by contrast, take about 24 hours.
Q84. Regarding Meiosis results: (i) Results in reduction of chromosome number by half. (ii) Four haploid daughter cells are formed. (iii) Restores the diploid phase upon fertilization.
Correct Answer: (c)
Meiosis reduces chromosome number from 2n to n (i). It produces four haploid cells (ii). Fertilisation of gametes restores the diploid chromosome number (iii). All correct.
Q85. Assertion: The nuclear membrane reappears during telophase.
Reason: Telophase is the final stage of karyokinesis.
Correct Answer: (b)
Both are true: nuclear membrane reforms in telophase, and telophase is the last stage of nuclear division. However, being the final stage does not explain why the membrane reforms; it reforms to re‑establish the nucleus. Thus, the reason is not the correct explanation.
Q86. Select the correct statements about Pachytene: (i) Four chromatids of each bivalent become distinct (tetrad). (ii) Appearance of recombination nodules. (iii) Recombination is completed by the end of this stage.
Correct Answer: (c)
In pachytene, tetrads are visible (i). Recombination nodules appear (ii). Crossing over is completed by the end of pachytene (iii). All true.
Q87. During Anaphase I, what happens to the sister chromatids?
Correct Answer: (b)
In Anaphase I, homologous chromosomes are pulled to opposite poles, but sister chromatids remain joined at their centromeres. This is a key difference from mitotic anaphase (where sister chromatids separate). Separation of sister chromatids occurs in Anaphase II.
Q88. Significance of Meiosis includes: (i) Conservation of specific chromosome number across generations. (ii) Increase in genetic variability. (iii) Basis of evolution.
Correct Answer: (c)
Meiosis maintains chromosome number from generation to generation (i). It creates genetic variability (ii). Variation is the basis of evolution (iii). All are correct.
Q89. The stage of Prophase I where synapsis occurs is:
Correct Answer: (b)
Synapsis, the pairing of homologous chromosomes, takes place during zygotene. It involves the formation of the synaptonemal complex between homologues. This pairing is essential for crossing over and genetic recombination.
Q90. The splitting of centromeres and separation of chromatids occurs during:
Correct Answer: (c)
During anaphase, the centromeres divide, allowing sister chromatids to separate. Each chromatid becomes an independent chromosome moving to opposite poles. This ensures equal distribution of genetic material to daughter cells.
Q91. Match the proteins involved:
A. Tubulin
Centrioles / Microtubules
B. Recombinase
Crossing over
Correct Answer: (a)
Tubulin is the protein subunit of microtubules, which form centrioles and spindle fibres. Recombinase is the enzyme responsible for crossing over. Both matches are accurate.
Q92. The stage between two meiotic divisions is called:
Correct Answer: (b)
Interkinesis is the brief period between Meiosis I and Meiosis II. During interkinesis, there is no DNA replication (unlike interphase). It is typically short‑lived and may be followed directly by prophase II.
Q93. The beginning of diplotene is recognized by the dissolution of the:
Correct Answer: (a)
During diplotene, the synaptonemal complex disassembles, and homologous chromosomes begin to separate. However, they remain attached at chiasmata. This dissolution allows chromatids to become visible as distinct entities.
Q94. Regarding Metaphase, which are true? (i) Spindle fibres attach to kinetochores. (ii) Chromosomes are moved to the spindle equator. (iii) The metaphase plate is the plane of alignment.
Correct Answer: (c)
Spindle fibres attach to kinetochores at metaphase (i). Chromosomes align at the equator (ii). The metaphase plate is the equatorial plane (iii). All are true.
Q95. Splitting of centromeres in meiosis occurs during:
Correct Answer: (b)
Centromeres divide and sister chromatids separate only during Anaphase II. This resembles a mitotic anaphase and results in the formation of haploid chromosomes. Anaphase I separates homologous chromosomes, not sister chromatids.
Q96. Mitosis is also called as:
Correct Answer: (b)
Mitosis is termed equational division because the chromosome number in the daughter cells remains the same as the parent (2n → 2n). It ensures genetic stability and identical genetic complements. In contrast, meiosis is a reduction division.
Q97. Assertion: Karyokinesis is not always followed by cytokinesis.
Reason: This leads to the formation of syncytium.
Correct Answer: (a)
The assertion is true: nuclear division can occur without cytoplasmic division. The reason correctly states that this results in a multinucleate syncytium. Thus, the reason is the correct explanation for the assertion.
Q98. Regarding Interkinesis, which are true? (i) Stage between Meiosis I and II. (ii) No DNA replication occurs. (iii) Generally short-lived.
Correct Answer: (c)
Interkinesis is the gap between meiosis I and II (i). No DNA synthesis occurs (ii). It is typically short (iii). All correct.
Q99. Match the stages of Meiosis I:
Column I
Column II
A. Anaphase I
(I) Homologous chromosomes separate
B. Telophase I
(II) Dyad of cells
C. Metaphase I
(III) Bivalents align at equator
Correct Answer: (a)
Anaphase I: homologous chromosomes separate (I). Telophase I results in two cells (dyad) (II). Metaphase I: bivalents align at the equatorial plate (III). Thus, A–I, B–II, C–III.
Q100. Identify the correct statements about Interphase: (i) It is divided into G1, S and G2 phases. (ii) Cell division proper lasts for only an hour. (iii) Cell prepares for division by undergoing DNA replication.
Correct Answer: (c)
Interphase has G1, S, and G2 (i). M phase in human cells is about 1 hour (ii). During interphase, DNA replication occurs in S phase (iii). Hence, all are correct.