Chapter – 10
Cell Cycle And Cell Division
Q1. Meiosis in diploid organisms results in
(a) Production of gametes
(b) Reduction in the number of chromosomes
(c) Introduction of variation
(d) All of the above
Ans:
(d)‘ Meiosis in diploid organisms results in production of gametes, reduction in the number of chromosomes and introduction of variation.
Q2. At which stage of meiosis does the genetic constitution of gametes is finallydecided? –
(a) Metaphase-I
(b) Anaphase-II
(c) Metaphase-II
(d) Anaphase-I
Ans:
(d) At anaphase-I, stage of meiosis the genetic constitution of gametes is finally decided.
Q3. Meiosis occurs in organisms during
(a) Sexual reproduction
(b) Vegetative reproduction
(c) Both sexual and vegetative reproduction
(d) None of these
Ans:
(a) Meiosis occurs in organisms during sexual reproduction. The production of offspring by sexual reproduction includes the fusion of two gametes, each with a complete haploid set of chromosomes. Gametes are produced through meiosis.
Q4. During anaphase-I of meiosis
(a) Homologous chromosomes separate
(b) Non-homologous chromosomes separate
(c) Sister chromatids chromosomes separate
(d) Non Sister chromatids chromosomes separate
Ans:
(a) The homologous chromosomes separate, while sister chromatids remain associated at their centromeres. Separation of homologous chromosomes at anaphase is called disjunction.
Q5. Mitosis is characterised by
(a) Reduction division
(b) Equal division
(c) Both reduction and equal division
(d) Pairing of homologous chromo somes
Ans:
(b) Mitosis is the most dramatic period of the cell cycle, involving a major reorganisation of virtually all components of the cell. Since the number of anothe chromosomes in the parent and progeny cells is the same, it is also called as equational division.
Q6. A bivalent of meiosis-I consists of
(a) Two chromatids and one centromere
(b) Two chromatids and two centromeres
(c) Four chromatids and two centromeres
(d) Four chromatids and four centromeres.
Ans:
(c) A bivalent of meiosis-I consists of four chromatids and two centromeres.
Q7. Cells which are not dividing are likely to be at
(a) G,
(b) G2
(C) G0
(d) S phase
Ans:
(c) These cells that do not divide further exit G{ phase to enter an inactive stage is called quiescent stage (G0) of the cell cycle. G0 stage of cell denotes exit “of cell from cell cycle. During G0 stage of cell cycle, cell decides to undergo differentiation. Cells in G0 stage remain metabolically active but no longer proliferate unless called on to do so depending on the requirement of the organism.
Q8. Which of the events listed below is not observed during mitosis?
(a) Chromatin condensation
(b) Movement of centrioles to opposite poles
(c) Appearance of chromosomes with two chromatids joined together at the centromere
(d) Crossing over
Ans:
(d) Crossing over occurs in pachytene (it is a phase of meiosis-I). Crossing over is the exchange of genetic material (genes) between two homologous chromosomes. Crossing over is also an enzyme-mediated process and the enzyme involved is called recombinase. Crossing over leads to recombination of genetic material on the two chromosomes. Exchange of paternal and maternal chromosome material during pachytene is called crossing over.
Q9. Identify the wrong statement about meiosis.
(a) Pairing of homologous chromosomes
(b) Four haploid cells are formed
(c) At the end of meiosis number of chromosomes are reduced to half
(d) Two cycles of DNA replication occur.
Ans:
(d) Meiosis involves two sequential cycles of nuclear and cell division called meiosis-I and meiosis-II but only a single cycle of DNA replication.
Q10. Select the correct statement about G1 phase.
(a) Cell is metabolically inactive
(b) DNA in the cell does not replicate
(c) It is not a phase of synthesis of macromolecules
(d) Cell stops growing.
Ans:
(b) During Gj phase the ceil is metabolically active and continuously grows but does not replicate its DNA but proteins and RNA are synthesized.