Consider the following statements regarding the cell cycle and its phases:
(I) Human cells in culture divide approximately once every 24 hours, whereas yeast cells complete a cell cycle in about 90 minutes. (II) Interphase represents the phase between two successive M phases and accounts for more than 95% of the total cell cycle duration. (III) Cytoplasmic growth is a continuous process throughout the cell cycle, whereas DNA synthesis occurs only during one specific stage. (IV) DNA synthesis occurs continuously throughout the entire interphase.
Statement (I) is correct because a typical human cell in culture divides once every 24 hours, while yeast cells complete a cell cycle in about 90 minutes. Statement (II) is correct because interphase occupies more than 95% of the total cell cycle. Statement (III) is correct because cytoplasmic growth is continuous whereas DNA synthesis occurs only during the S phase. Statement (IV) is incorrect because DNA replication occurs only during the S phase, not throughout interphase.
Question 2 of 100
📘 CLASS XI
Consider the following statements regarding the stages of Interphase (G1, S, G2, G0):
(I) During the G1 phase, the cell is metabolically active and continuously grows, but does not replicate its DNA. (II) During the S phase, the amount of DNA per cell doubles (e.g., from 2C to 4C), and the chromosome number also doubles from 2n to 4n. (III) In animal cells, during the S phase, DNA replication begins in the nucleus, and the centriole duplicates in the cytoplasm. (IV) Cells in the quiescent stage (G0) exit the G1 phase; they remain metabolically active but no longer proliferate unless called on to do so.
Statement (I) is correct because G1 is a metabolically active growth phase without DNA replication. Statement (II) is incorrect because DNA content doubles during S phase, but chromosome number remains 2n. Statement (III) is correct because DNA replicates in the nucleus while centrioles duplicate in the cytoplasm. Statement (IV) is correct because G0 cells remain metabolically active but stop proliferating unless stimulated.
Question 3 of 100
📘 CLASS XI
Consider the following statements regarding Prophase of mitosis:
(I) Prophase is marked by the initiation of condensation of chromosomal material. (II) The centrosome, which duplicated during the S phase of interphase, begins to move towards opposite poles of the cell during prophase. (III) Mitotic apparatus consists of two asters together with spindle fibres. (IV) Under a microscope, cells at the end of prophase show prominent Golgi complexes, endoplasmic reticulum, nucleolus, and nuclear envelope.
Statement (I) is correct because chromosomal condensation begins during prophase. Statement (II) is correct because duplicated centrosomes move toward opposite poles. Statement (III) is correct because the mitotic apparatus consists of two asters and spindle fibres. Statement (IV) is incorrect because the Golgi complex, ER, nucleolus, and nuclear envelope disappear by the end of prophase.
Question 4 of 100
📘 CLASS XI
Consider the following statements regarding Metaphase of mitosis:
(I) The complete disintegration of the nuclear envelope marks the start of metaphase. (II) Metaphase is the stage at which the morphology of chromosomes is most easily studied. (III) Small disc-shaped structures at the surface of centromeres are called kinetochores, which serve as attachment sites for spindle fibres. (IV) During metaphase, centromeres split simultaneously and sister chromatids move to opposite poles.
Statement (I) is correct because complete breakdown of the nuclear envelope marks the beginning of metaphase. Statement (II) is correct because chromosomes are maximally condensed and easily studied. Statement (III) is correct because kinetochores provide attachment sites for spindle fibres. Statement (IV) is incorrect because centromere splitting and chromatid movement occur during anaphase.
Question 5 of 100
📘 CLASS XI
Consider the following statements regarding Anaphase and Telophase of mitosis:
(I) At the onset of anaphase, centromeres split simultaneously and sister chromatids separate to become daughter chromosomes. (II) During anaphase, as chromosomes move to opposite poles, the centromere leads toward the pole while chromosome arms trail behind. (III) During telophase, chromosomes cluster at opposite poles, decondense, and lose their individual identity. (IV) The nucleolus, Golgi complex, and ER reform during telophase.
Statement (I) is correct because centromeres split simultaneously and sister chromatids separate during anaphase. Statement (II) is correct because centromeres lead while chromosome arms trail during poleward movement. Statement (III) is correct because chromosomes decondense and lose their distinct identity during telophase. Statement (IV) is correct because the nucleolus, Golgi complex, ER, and nuclear envelope reform during telophase.
Question 6 of 100
📘 CLASS XI
Consider the following statements regarding Cytokinesis and mitotic variations:
(I) In animal cells, cytokinesis occurs by the appearance of a furrow in the plasma membrane that deepens centripetally. (II) In plant cells, wall formation starts in the centre of the cell and grows outward (centrifugally) to meet lateral walls. (III) The precursor of the new cell wall in plants is called the cell-plate, which represents the middle lamella. (IV) If karyokinesis is not followed by cytokinesis, a multinucleate condition called syncytium arises (e.g., liquid endosperm in coconut).
Statement (I) is correct because animal cytokinesis occurs by the formation of a cleavage furrow that deepens centripetally. Statement (II) is correct because plant cells form a cell plate centrally that grows centrifugally toward the lateral walls. Statement (III) is correct because the cell plate represents the precursor of the middle lamella. Statement (IV) is correct because failure of cytokinesis after karyokinesis produces a multinucleate syncytium, as seen in coconut liquid endosperm.
Question 7 of 100
📘 CLASS XI
Consider the following statements regarding Leptotene, Zygotene, and Pachytene of Meiotic Prophase I:
(I) Chromosomes become gradually visible under the light microscope during leptotene. (II) Synapsis (pairing of homologous chromosomes) and synaptonemal complex formation occur during zygotene. (III) Recombination nodules appear and crossing over occurs between sister chromatids of homologous chromosomes during pachytene. (IV) Crossing over is an enzyme-mediated process catalyzed by recombinase.
Statement (I) is correct because chromosomes gradually become visible during leptotene. Statement (II) is correct because synapsis and synaptonemal complex formation occur during zygotene. Statement (III) is incorrect because crossing over occurs between non-sister chromatids of homologous chromosomes, not sister chromatids. Statement (IV) is correct because recombinase catalyzes crossing over.
Question 8 of 100
📘 CLASS XI
Consider the following statements regarding Diplotene and Diakinesis of Meiotic Prophase I:
(I) The beginning of diplotene is recognized by the dissolution of the synaptonemal complex. (II) X-shaped structures representing sites of crossovers are called chiasmata and are observed in diplotene. (III) In oocytes of some vertebrates, diplotene can last for months or years. (IV) Diakinesis is marked by the terminalisation of chiasmata and represents the transition to metaphase I.
Statement (I) is correct because diplotene begins with dissolution of the synaptonemal complex. Statement (II) is correct because chiasmata become visible during diplotene. Statement (III) is correct because vertebrate oocytes may remain arrested in diplotene for months or years. Statement (IV) is correct because diakinesis is characterized by terminalisation of chiasmata and transition into metaphase I.
Question 9 of 100
📘 CLASS XI
Consider the following statements comparing Meiosis I and Meiosis II:
(I) During Anaphase I, homologous chromosomes separate, while sister chromatids remain associated at their centromeres. (II) During Anaphase II, centromeres split simultaneously, allowing sister chromatids to move toward opposite poles. (III) The stage between Meiosis I and Meiosis II is called interkinesis, during which active DNA replication occurs. (IV) Meiosis I produces a dyad of haploid cells, whereas Meiosis II ends with a tetrad of four haploid daughter cells.
Statement (I) is correct because homologous chromosomes separate during anaphase I while sister chromatids remain joined. Statement (II) is correct because centromeres divide during anaphase II, allowing sister chromatids to separate. Statement (III) is incorrect because interkinesis does not involve DNA replication. Statement (IV) is correct because meiosis I produces a dyad of haploid cells and meiosis II produces a tetrad of four haploid daughter cells.
Question 10 of 100
📘 CLASS XI
Consider the following statements regarding the significance of Mitosis and Meiosis:
(I) Mitosis restores the nucleo-cytoplasmic ratio in cells that have grown large. (II) Mitotic divisions in apical and lateral cambium result in continuous growth of plants throughout life. (III) Meiosis conserves the specific chromosome number of a species across generations in sexually reproducing organisms. (IV) Meiosis decreases genetic variability within a population from one generation to the next.
Statement (I) is correct because mitosis restores the nucleo-cytoplasmic ratio disturbed by cell growth. Statement (II) is correct because apical and lateral meristems undergo continuous mitotic divisions throughout plant life. Statement (III) is correct because meiosis halves the chromosome number so that fertilization restores the diploid chromosome number, maintaining species chromosome constancy. Statement (IV) is incorrect because meiosis increases genetic variability through crossing over and independent assortment.
