Consider the following statements regarding the events occurring during the Synthesis (S) phase of the cell cycle:
(I) The amount of DNA per cell doubles during the S phase, increasing from 2C to 4C if the initial amount is 2C. (II) The chromosome number doubles from 2n to 4n during the S phase in human somatic cells. (III) In animal cells, DNA replication begins in the nucleus, while centriole duplication occurs in the cytoplasm during the S phase. (IV) Most organelle duplication takes place during the S phase alongside DNA synthesis.
Which of the above statements are correct?
Statement (I) is correct because DNA content doubles from 2C to 4C during S phase. Statement (II) is incorrect because chromosome number remains unchanged although DNA content doubles. Statement (III) is correct because DNA replication occurs in the nucleus while centrioles duplicate in the cytoplasm in animal cells. Statement (IV) is incorrect because most organelle duplication occurs during the G1 phase.
Question 72 of 100
📘 CLASS XI
Consider the following statements regarding the Quiescent stage (G0) and mitotic cell division in different organisms:
(I) Cells that do not divide further exit the G1 phase to enter an inactive stage called the quiescent stage (G0). (II) Cells in the G0 stage remain metabolically active but no longer proliferate unless requested based on the requirement of the organism. (III) In animals, mitotic cell division is restricted strictly to diploid somatic cells without any known exceptions. (IV) Plants can display mitotic cell divisions in both haploid and diploid cells, enabling alternation of generations.
Which of the above statements are correct?
Statement (I) is correct because non-dividing cells enter G0 after G1. Statement (II) is correct because G0 cells remain metabolically active and can re-enter the cell cycle if required. Statement (III) is incorrect because haploid male honey bees are an exception. Statement (IV) is correct because mitosis occurs in both haploid and diploid plant cells.
Question 73 of 100
📘 CLASS XI
Consider the following statements regarding Prophase of Mitosis and the formation of the Mitotic Apparatus:
(I) Prophase is marked by the initiation of condensation of chromosomal material. (II) Asters are microtubule arrays that radiate outward from each duplicated centrosome. (III) The mitotic apparatus consists of two asters together with the spindle fibres. (IV) Under a microscope, cells viewed at the end of prophase show a distinct nucleolus, endoplasmic reticulum, and nuclear envelope.
Which of the above statements are correct?
Statement (I) is correct because chromatin condensation begins during prophase. Statement (II) is correct because asters are radial arrays of microtubules around centrosomes. Statement (III) is correct because the mitotic apparatus consists of two asters and spindle fibres. Statement (IV) is incorrect because the nucleolus, ER and nuclear envelope disappear by late prophase.
Question 74 of 100
📘 CLASS XI
Consider the following statements regarding chromosome orientation and structures during Metaphase of Mitosis:
(I) The complete breakdown of the nuclear envelope defines the commencement of metaphase. (II) Metaphase is the stage at which chromosome morphology is most easily studied because chromosome condensation is complete. (III) Disc-shaped structures called kinetochores are present on centromeres and serve as attachment sites for spindle fibres. (IV) Metaphase is characterized by all chromosomes aligning at the equator, with each sister chromatid connected by its kinetochore to spindle fibres from opposite poles.
Which of the above statements are correct?
All four statements are correct. Metaphase begins after complete nuclear envelope breakdown. Chromosomes are maximally condensed and easiest to study. Kinetochores provide spindle attachment sites, and sister chromatids attach to spindle fibres from opposite poles.
Question 75 of 100
📘 CLASS XI
Consider the following statements regarding cellular dynamics during Anaphase and Telophase of Mitosis:
(I) At the onset of anaphase, centromeres split simultaneously and sister chromatids separate into daughter chromosomes. (II) During anaphase movement, centromeres trail behind while the arms of the chromosomes lead toward opposite poles. (III) During telophase, chromosomes reach opposite poles, decondense, and lose their discrete individual identity. (IV) The nuclear envelope, nucleolus, Golgi complex, and ER reform during telophase.
Which of the above statements are correct?
Statement (I) is correct because anaphase begins with centromere splitting and separation of sister chromatids. Statement (II) is incorrect because centromeres lead toward the poles while chromosome arms trail behind. Statement (III) is correct because chromosomes decondense during telophase. Statement (IV) is correct because the nuclear envelope, nucleolus, Golgi complex and ER reform during telophase.
Question 76 of 100
📘 CLASS XI
Consider the following statements regarding Cytokinesis and Syncytium Formation:
(I) Cytokinesis in animal cells involves the formation of a plasma membrane cleavage furrow that deepens centripetally. (II) Plant cell wall formation starts at the cell periphery and grows centrifugally toward the cell center. (III) The simple precursor of the new cell wall in plant cells is the cell-plate, which represents the middle lamella. (IV) If karyokinesis is not followed by cytokinesis, a multinucleate condition called a syncytium arises (e.g., liquid endosperm in coconut).
Which of the above statements are correct?
Statement (I) is correct because animal cytokinesis proceeds via a cleavage furrow deepening centripetally. Statement (II) is incorrect because plant cell wall formation begins at the center of the cell and grows centrifugally outward. Statement (III) is correct because the cell plate develops into the middle lamella. Statement (IV) is correct because failure of cytokinesis after karyokinesis produces a multinucleate syncytium, as seen in coconut liquid endosperm.
Question 77 of 100
📘 CLASS XI
Consider the following statements regarding the substages of Meiotic Prophase I (Leptotene, Zygotene, Pachytene):
(I) Chromosome compaction continues throughout the leptotene stage. (II) Pairing of homologous chromosomes (synapsis) and assembly of synaptonemal complexes take place during zygotene. (III) Bivalents or tetrads are formed during zygotene but become more distinctly visible during pachytene. (IV) Crossing over occurs during pachytene between sister chromatids of homologous chromosomes.
Which of the above statements are correct?
Statement (I) is correct because chromosome compaction continues throughout leptotene. Statement (II) is correct because synapsis and synaptonemal complex formation occur during zygotene. Statement (III) is correct because bivalents become clearly visible as tetrads during pachytene. Statement (IV) is incorrect because crossing over occurs between non-sister chromatids of homologous chromosomes.
Question 78 of 100
📘 CLASS XI
Consider the following statements regarding Diplotene, Diakinesis, and Metaphase I of Meiosis:
(I) The beginning of diplotene is recognized by the dissolution of the synaptonemal complex. (II) Chiasmata are X-shaped structures formed where recombined homologous chromosomes remain attached in diplotene. (III) Diakinesis is marked by terminalisation of chiasmata and transition to metaphase I. (IV) During Metaphase I, bivalent chromosomes align at the equatorial plate and spindle fibres attach to kinetochores of homologous chromosomes.
Which of the above statements are correct?
All four statements are correct. Diplotene begins with dissolution of the synaptonemal complex and appearance of chiasmata. Diakinesis is marked by terminalisation of chiasmata and transition to metaphase I. During Metaphase I, bivalents align at the equator and spindle fibres attach to kinetochores of homologous chromosomes.
Question 79 of 100
📘 CLASS XI
Consider the following statements regarding Anaphase I, Interkinesis, and Meiosis II:
(I) Homologous chromosomes separate during Anaphase I, while sister chromatids remain attached at their centromeres. (II) Interkinesis is a brief stage between Meiosis I and Meiosis II where DNA undergoes active replication. (III) Meiosis II resembles a normal mitotic division and initiates immediately after cytokinesis I. (IV) During Anaphase II, centromeres split simultaneously, allowing sister chromatids to move toward opposite poles.
Which of the above statements are correct?
Statement (I) is correct because homologous chromosomes separate during Anaphase I while sister chromatids remain joined. Statement (II) is incorrect because interkinesis does not involve DNA replication. Statement (III) is correct because Meiosis II is an equational division resembling mitosis. Statement (IV) is correct because centromeres split during Anaphase II, separating sister chromatids.
Question 80 of 100
📘 CLASS XI
Consider the following statements regarding the Significance of Mitosis and Meiosis:
(I) Mitosis maintains the chromosome number (equational division) and restores the nucleo-cytoplasmic ratio in growing cells. (II) Mitotic divisions in apical and lateral cambium meristems sustain continuous growth of plants throughout life. (III) Meiosis reduces the chromosome number by half to conserve the specific chromosome number of a species across generations. (IV) Meiosis increases genetic variability within a population from one generation to the next, which is important for evolution.
Which of the above statements are correct?
All four statements are correct. Mitosis maintains chromosome number and restores the nucleo-cytoplasmic ratio. Continuous plant growth depends on mitotic divisions in apical and lateral meristems. Meiosis halves chromosome number to maintain species chromosome number after fertilization and generates genetic variation through recombination and independent assortment.
