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NEET-XI-Biology

10: Cell Cycle and Cell Division

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    10 - Cell Cycle and Cell Division
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    Section : I
    Page No 171:
  • Qstn #1
    What is the average cell cycle span for a mammalian cell?
    Ans : The average cell cycle span for a mammalian cell is approximately 24 hours.
  • Qstn #2
    Distinguish cytokinesis from karyokinesis.
    Ans :


    Cytokinesis


    Karyokinesis


    (i)

    		 Cytokinesis is the biological process involving the division of a cell’s cytoplasm during mitosis or meiosis.


    (i)

    		 Karyokinesis is the biological process involving the division of a cell’s nucleus during mitosis or meiosis.


    (ii)

    		 Stages such as prophase, metaphase, anaphase, and telophase are not present in cytokinesis.


    (ii)

    		 It is divided into four stages –prophase, metaphase, anaphase, and telophase


  • Qstn #3
    Describe the events taking place during interphase.
    Ans : Interphase involves a series of changes that prepare a cell for division. It is the period during which the cell experiences growth and DNA replication in an orderly manner. Interphase is divided into three phases.

    (i) G1 phase

    (ii) S phase

    (iii) G2 phase

    G1 phase - It is the stage during which the cell grows and prepares its DNA for replication. In this phase, the cell is metabolically active.

    S phase - It is the stage during which DNA synthesis occurs. In this phase, the amount of DNA (per cell) doubles, but the chromosome number remains the same.

    G2 phase - In this phase, the cell continues to grow and prepares itself for division. The proteins and RNA required for mitosis are synthesised during this stage.


  • Qstn #4
    What is G0 (quiescent phase) of cell cycle?
    Ans : G0 or quiescent phase is the stage wherein cells remain metabolically active, but do not proliferate unless called to do so. Such cells are used for replacing the cells lost during injury.
  • Qstn #5
    Why is mitosis called equational division?
    Ans : Mitosis is the process of cell division wherein the chromosomes replicate and get equally distributed into two daughter cells. The chromosome number in each daughter cell is equal to that in the parent cell, i.e., diploid. Hence, mitosis is known as equational division.
  • Qstn #6
    Name the stage of cell cycle at which one of the following events occur:
  • Qstn #6-i
    Chromosomes are moved to spindle equator
    Ans : Metaphase
  • Qstn #6-ii
    Centromere splits and chromatids separate
    Ans : Anaphase
  • Qstn #6-iii
    Pairing between homologous chromosomes takes place
    Ans : Zygotene of meiosis I
  • Qstn #6-iv
    Crossing over between homologous chromosomes takes place
    Ans : Pachytene of meiosis I
  • Qstn #7
    Describe the following:
    (a) synapsis (b) bivalent (c) chiasmata

    Draw a diagram to illustrate your answer.
    Ans : null (a) Synapsis

    The pairing of homologous chromosomes is called synapsis. This occurs during the second stage of prophase I or zygotene.


    (b) Bivalent

    Bivalent or tetrad is a pair of synapsed homologous chromosomes. They are formed during the zygotene stage of prophase I of meiosis.


    (c) Chiasmata

    Chiasmata is the site where two non-sister chromatids of homologous chromosomes have crossed over. It represents the site of cross-over. It is formed during the diplotene stage of prophase I of meiosis.


  • #7-a
    synapsis
    Ans : Synapsis

    The pairing of homologous chromosomes is called synapsis. This occurs during the second stage of prophase I or zygotene.


  • #7-b
    bivalent
    Ans : Bivalent

    Bivalent or tetrad is a pair of synapsed homologous chromosomes. They are formed during the zygotene stage of prophase I of meiosis.


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