Class XI Biology
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100 questions in this chapter
Question 11 of 100
š CLASS XI
Consider the following statements regarding the Quiescent stage (Gā) and mitotic cell division in organisms:
(I) Heart cells and many adult animal cells do not exhibit division and exit the Gā phase to enter an inactive stage called Gā. (II) Cells in the Gā 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 only to diploid somatic cells, with exceptions seen in haploid male honey bees. (IV) In plants, mitotic divisions can occur in both haploid and diploid cells, enabling alternation of generations.
Statement (I) is correct because adult animal cells like heart cells exit Gā and enter Gā. Statement (II) is correct because Gā cells remain metabolically active but divide only when required. Statement (III) is correct because mitosis generally occurs in diploid somatic cells, with the notable exception of haploid male honey bees. Statement (IV) is correct because plants undergo mitosis in both haploid and diploid phases during alternation of generations.
Question 12 of 100
š CLASS XI
Consider the following statements regarding chromosome morphology and Metaphase:
(I) At metaphase, each chromosome consists of two sister chromatids held together by a centromere. (II) Disc-shaped structures called kinetochores are present on the surface of centromeres. (III) Spindle fibres attach to kinetochores of chromosomes, aligning them at the equator during metaphase. (IV) The plane of alignment of chromosomes at metaphase is referred to as the metaphase plate.
Statement (I) is correct because metaphase chromosomes consist of two sister chromatids joined at the centromere. Statement (II) is correct because kinetochores are disc-shaped structures located on centromeres. Statement (III) is correct because spindle fibres attach to kinetochores and align chromosomes at the equator. Statement (IV) is correct because this equatorial plane is called the metaphase plate.
Question 13 of 100
š CLASS XI
Consider the following statements regarding the events of Anaphase in mitosis:
(I) Centromeres of chromosomes split during metaphase to prepare for movement. (II) During anaphase, sister chromatids separate and become individual daughter chromosomes of future nuclei. (III) As chromosomes move toward opposite poles, centromeres are directed toward the poles while the arms trail behind. (IV) Homologous chromosome separation occurs during mitotic anaphase.
Statement (I) is incorrect because centromeres split at the onset of anaphase, not metaphase. Statement (II) is correct because sister chromatids separate to become daughter chromosomes. Statement (III) is correct because centromeres lead chromosome movement while the arms trail behind. Statement (IV) is incorrect because homologous chromosomes separate during anaphase I of meiosis, not mitosis.
Question 14 of 100
š CLASS XI
Consider the following statements regarding Cytokinesis in plant and animal cells:
(I) Animal cytokinesis involves the formation of a cell furrow in the plasma membrane that deepens centripetally. (II) Plant cytokinesis occurs via cell wall formation that starts at the cell periphery and moves inward. (III) The precursor of the new cell wall in plant cells is the cell plate, which forms centrally and grows centrifugally. (IV) The cell plate represents the middle lamella between the walls of adjacent plant cells.
Statement (I) is correct because animal cells divide by formation of a centripetal cleavage furrow. Statement (II) is incorrect because plant cell wall formation begins at the centre and grows centrifugally. Statement (III) is correct because the cell plate originates centrally and expands outward. Statement (IV) is correct because the cell plate develops into the middle lamella separating adjacent cell walls.
Question 15 of 100
š CLASS XI
Consider the following statements regarding Leptotene and Zygotene of Prophase I:
(I) Compaction of chromosomes continues throughout the leptotene stage. (II) Synapsis involves the pairing of homologous chromosomes during zygotene. (III) The formation of the synaptonemal complex is completed during pachytene. (IV) The complex formed by a pair of synapsed homologous chromosomes is called a bivalent or a tetrad.
Statement (I) is correct because chromosome compaction continues during leptotene. Statement (II) is correct because homologous chromosome pairing (synapsis) occurs during zygotene. Statement (III) is incorrect because the synaptonemal complex forms during zygotene, not pachytene. Statement (IV) is correct because paired homologous chromosomes constitute a bivalent or tetrad.
Question 16 of 100
š CLASS XI
Consider the following statements regarding Pachytene stage of Meiotic Prophase I:
(I) Four chromatids of each bivalent chromosome become distinct and clearly visible as a tetrad during pachytene. (II) Pachytene is characterized by the appearance of recombination nodules where crossing over occurs. (III) Crossing over is the exchange of genetic material between sister chromatids of homologous chromosomes. (IV) Crossing over is an enzyme-mediated process involving the enzyme recombinase.
Which of the above statements are correct?
Statement (I) is correct because tetrads become clearly visible during pachytene. Statement (II) is correct because recombination nodules mark the sites of crossing over. Statement (III) is incorrect because crossing over occurs between non-sister chromatids of homologous chromosomes. Statement (IV) is correct because crossing over is catalyzed by the enzyme complex recombinase.
Question 17 of 100
š CLASS XI
Consider the following statements regarding Diplotene and Diakinesis:
(I) Dissolution of the synaptonemal complex occurs at the beginning of diplotene. (II) X-shaped structures called chiasmata are formed due to separation of recombined homologous chromosomes except at crossing over sites. (III) Diakinesis is marked by the terminalisation of chiasmata. (IV) By the end of diakinesis, the nucleolus disappears and the nuclear envelope breaks down.
Which of the above statements are correct?
Statement (I) is correct because diplotene begins with the breakdown of the synaptonemal complex. Statement (II) is correct because homologous chromosomes separate except at chiasmata, producing X-shaped figures. Statement (III) is correct because terminalisation of chiasmata characterizes diakinesis. Statement (IV) is correct because the nucleolus disappears and the nuclear envelope breaks down by the end of diakinesis.
Question 18 of 100
š CLASS XI
Consider the following statements regarding Metaphase I and Anaphase I of Meiosis I:
(I) During Metaphase I, bivalent chromosomes align on the equatorial plate in two rows. (II) Spindle fibres attach to kinetochores of homologous chromosomes from opposite poles during Metaphase I. (III) During Anaphase I, homologous chromosomes separate, while sister chromatids remain attached at centromeres. (IV) Centromeres split during Anaphase I to allow chromosome separation.
Which of the above statements are correct?
Statement (I) is correct because bivalents align on the equatorial plate during Metaphase I. Statement (II) is correct because spindle fibres attach to kinetochores of homologous chromosomes. Statement (III) is correct because homologous chromosomes separate while sister chromatids remain joined at their centromeres. Statement (IV) is incorrect because centromeres split during Anaphase II, not Anaphase I.
Question 19 of 100
š CLASS XI
Consider the following statements regarding Meiosis II:
(I) Meiosis II is initiated immediately after cytokinesis I, usually before chromosomes have fully elongated. (II) In contrast to Meiosis I, Meiosis II resembles a normal mitotic division. (III) During Anaphase II, centromeres split simultaneously, allowing sister chromatids to move to opposite poles. (IV) Meiosis II converts two haploid cells into four diploid cells.
Which of the above statements are correct?
Statement (I) is correct because Meiosis II begins soon after cytokinesis I before chromosomes completely elongate. Statement (II) is correct because Meiosis II is an equational division resembling mitosis. Statement (III) is correct because centromeres divide during Anaphase II, separating sister chromatids. Statement (IV) is incorrect because Meiosis II produces four haploid daughter cells, not diploid cells.
Question 20 of 100
š CLASS XI
Consider the following comparative statements between Mitosis and Meiosis:
(I) Mitosis maintains the chromosome number (equational division), whereas Meiosis reduces it by half (reductional division). (II) DNA replication occurs prior to both Mitosis and Meiosis I, but not prior to Meiosis II. (III) Pairing of homologous chromosomes (synapsis) occurs during prophase of both Mitosis and Meiosis I. (IV) Meiosis generates genetic variability through crossing over and independent assortment, whereas Mitosis produces genetically identical cells.
Which of the above statements are correct?
Statement (I) is correct because mitosis is an equational division while meiosis is reductional. Statement (II) is correct because DNA replication occurs before Mitosis and Meiosis I but not before Meiosis II. Statement (III) is incorrect because synapsis occurs only during Prophase I of meiosis. Statement (IV) is correct because meiosis generates genetic variation through crossing over and independent assortment, whereas mitosis produces genetically identical daughter cells.
