Consider the following statements regarding the duration and basic phases of the cell cycle:
(I) A typical human cell in culture divides approximately once every 24 hours, whereas cell division proper (M phase) lasts for only about an hour. (II) Interphase represents the phase between two successive M phases and lasts for less than 50% of the total cell cycle duration. (III) Yeast cells can progress through a complete cell cycle in about 90 minutes. (IV) Interphase is a resting phase where the cell is metabolically inactive and only prepares for nuclear division mechanically.
Which of the above statements are correct?
Statement (I) is correct because a typical human cell completes the cell cycle in about 24 hours, with M phase lasting about one hour. Statement (II) is incorrect because interphase occupies more than 95% of the cell cycle. Statement (III) is correct because yeast cells complete the cell cycle in about 90 minutes. Statement (IV) is incorrect because interphase is metabolically active and involves growth and DNA replication.
Question 52 of 100
📘 CLASS XI
Consider the following statements regarding events occurring in the S phase of interphase:
(I) During the S phase, the amount of DNA per cell doubles (e.g., from 2C to 4C). (II) The chromosome number doubles from 2n to 4n during the S phase in diploid animal cells. (III) In animal cells, centriole duplication takes place in the cytoplasm while DNA replication occurs in the nucleus during the S phase. (IV) Higher plant cells also undergo centriole duplication in the cytoplasm during the S phase.
Which of the above statements are correct?
Statement (I) is correct because DNA content doubles during S phase. Statement (II) is incorrect because chromosome number remains unchanged during DNA replication. Statement (III) is correct because DNA replication occurs in the nucleus while centrioles duplicate in the cytoplasm of animal cells. Statement (IV) is incorrect because higher plant cells lack centrioles.
Question 53 of 100
📘 CLASS XI
Consider the following statements regarding the characteristic features of Prophase in mitosis:
(I) Prophase is marked by the initiation of condensation of chromosomal material. (II) Microtubules radiating outward from each duplicated centrosome are called asters. (III) The two asters together with spindle fibres form the mitotic apparatus. (IV) Under a microscope, cells at the end of prophase show a distinct nucleolus, nuclear envelope, and Golgi complex.
Which of the above statements are correct?
Statement (I) is correct because chromatin condensation begins during prophase. Statement (II) is correct because microtubules radiating from centrosomes are called asters. Statement (III) is correct because two asters together with spindle fibres constitute the mitotic apparatus. Statement (IV) is incorrect because the nucleolus, nuclear envelope, Golgi complex, and ER disappear by the end of prophase.
Question 54 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) Chromosome morphology is most easily studied at metaphase because condensation of chromosomes is completed. (III) Kinetochores are disc-shaped structures on the centromere that serve as attachment sites for spindle fibres. (IV) At metaphase, one chromatid of a chromosome is attached by its kinetochore to spindle fibres from both poles simultaneously.
Which of the above statements are correct?
Statement (I) is correct because metaphase begins after complete nuclear envelope breakdown. Statement (II) is correct because chromosomes are maximally condensed at metaphase. Statement (III) is correct because kinetochores serve as spindle fibre attachment sites. Statement (IV) is incorrect because sister chromatids attach to opposite poles, not a single chromatid to both poles.
Question 55 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) As chromosomes move away from the equator in anaphase, centromeres trail behind while chromosome arms lead toward the pole. (III) During telophase, chromosomes cluster at opposite poles, decondense, and lose their individual identity. (IV) The nucleolus, Golgi complex, and endoplasmic reticulum reform during telophase.
Which of the above statements are correct?
Statement (I) is correct because anaphase begins with centromere splitting and chromatid separation. 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 nucleolus, Golgi complex, endoplasmic reticulum, and nuclear envelope reform during telophase.
Question 56 of 100
📘 CLASS XI
Consider the following statements regarding Cytokinesis and Syncytium formation:
(I) Animal cell cytokinesis is achieved by the appearance of a furrow in the plasma membrane that deepens centripetally. (II) Plant cell wall formation starts in the centre of the cell and grows centrifugally to meet existing lateral walls. (III) The simple precursor of the new plant cell wall is the cell-plate, which represents the primary cell wall. (IV) Liquid endosperm in coconut is an example of a multinucleate condition (syncytium) formed when karyokinesis is not followed by cytokinesis.
Which of the above statements are correct?
Statement (I) is correct because animal cytokinesis proceeds through a cleavage furrow that deepens centripetally. Statement (II) is correct because plant cell wall formation begins centrally and grows centrifugally. Statement (III) is incorrect because the cell plate develops into the middle lamella, not the primary cell wall. Statement (IV) is correct because failure of cytokinesis after karyokinesis produces a multinucleate syncytium such as coconut liquid endosperm.
Question 57 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 as compaction continues throughout leptotene. (II) Pairing of homologous chromosomes (synapsis) accompanied by synaptonemal complex formation occurs during zygotene. (III) Bivalents or tetrads are more clearly visible during pachytene than during zygotene. (IV) Crossing over during pachytene involves exchange of genetic material between sister chromatids of the same chromosome.
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 tetrads become distinctly visible during pachytene. Statement (IV) is incorrect because crossing over occurs between non-sister chromatids of homologous chromosomes.
Question 58 of 100
📘 CLASS XI
Consider the following statements regarding Pachytene, Diplotene, and Diakinesis of Meiotic Prophase I:
(I) Crossing over is an enzyme-mediated process catalyzed by the enzyme complex recombinase. (II) The beginning of diplotene is recognized by the dissolution of the synaptonemal complex. (III) X-shaped structures called chiasmata are formed where recombined homologous chromosomes remain attached during diplotene. (IV) Terminalisation of chiasmata and breakdown of the nuclear envelope mark diakinesis.
Which of the above statements are correct?
All four statements are correct. Crossing over is mediated by recombinase. Diplotene begins with dissolution of the synaptonemal complex. Chiasmata become visible where homologous chromosomes remain attached. Diakinesis is characterized by terminalisation of chiasmata along with disappearance of the nucleolus and nuclear envelope.
Question 59 of 100
📘 CLASS XI
Consider the following statements regarding Meiosis I (Anaphase I & Telophase I) and Interkinesis:
(I) Homologous chromosomes separate during Anaphase I, while sister chromatids remain attached at their centromeres. (II) Cytokinesis following Telophase I yields a dyad of cells. (III) Interkinesis is the stage between Meiosis I and Meiosis II during which active DNA replication occurs. (IV) Chromosomes in Telophase I reach the extremely extended state characteristic of the interphase nucleus.
Which of the above statements are correct?
Statement (I) is correct because homologous chromosomes separate while sister chromatids remain attached. Statement (II) is correct because cytokinesis after Telophase I forms a dyad. Statement (III) is incorrect because DNA replication does not occur during interkinesis. Statement (IV) is incorrect because chromosomes do not attain the fully extended interphase condition.
Question 60 of 100
📘 CLASS XI
Consider the following statements regarding Meiosis II and the Significance of Cell Division:
(I) Meiosis II resembles a normal mitotic division and concludes with the formation of a tetrad of four haploid daughter cells. (II) Centromeres split simultaneously during Anaphase II, allowing sister chromatids to move toward opposite poles. (III) Mitosis helps restore the nucleo-cytoplasmic ratio disturbed by cell growth. (IV) Meiosis decreases genetic variability within a population from one generation to the next.
Which of the above statements are correct?
Statement (I) is correct because Meiosis II is an equational division producing four haploid daughter cells. Statement (II) is correct because centromeres split during Anaphase II. Statement (III) is correct because mitosis restores the nucleo-cytoplasmic ratio disturbed during cell growth. Statement (IV) is incorrect because meiosis increases genetic variability through crossing over and independent assortment.
