• Cell Division - Mitosis And Meiosis (Short Answers)


     Cell Division - Short Answer Questions:


    What is meant by cell cycle?

    The sequence of events by which

    1.  a cell duplicates its genome during one specific stage

    2.  synthesizes the other constituent of the cell that is organelles

    3.  eventually divides into two daughter cells


    Why do cells divide?

    1. Replace old dead or damaged cells

    2.  to provide growth to living organisms by producing more cell

    3.  to divide genome from parent cell to daughter cells


    How do cells know when to divide?

    Cells communicate with each other using chemical signals. These signals tell the cell when to start and when to stop the division.

     If cells are not communicated to stop dividing at the right time, it leads to a situation called “cancer”.


    Name two cell organelles having their own DNA material.

    1. Plastid

    2. Mitochondria


    What happens when cycle checkpoints are not maintained? 

    1. This situation is called as cancer

    2.  mutation occurs in the cell

    3.  cell continues to divide 


    What is Karyokinesis?

    Karyokinesis refers to nuclear division in which nuclear material i.e. the chromosomes replicate and separate.


    What is Cytokinesis?

    Cytokinesis refers to division of cytoplasm during the cell division cycle.


    Why do all cells in sexually reproducing organisms not divide in similar manner?

    1. To provide genetic diversity to offsprings so that they differ front he parent and differ from each other also


    What is Mitosis?

    • Mitosis is a process of cell division in which a single cell divides into two  daughter cells.  

    • Each of the daughter cells produced after Mitosis has the same number of chromosomes as the parent cell.

    • Mitosis helps in basic growth and repair of damaged cells.

    • Mitosis does not happen in reproductive cells i.e. sperms and ovum.


    What is Meiosis?

    • Meiosis is process of cell division in which a single cell divides into two daughter cells

    •  the daughter cell have the number of chromosomes as the parent cell

    • Meiosis happens only in reproductive cells that is Sperm and Ovum

    • Helps in Genetic diversity between parent cell and the daughter cells and also amongst daughter cells

    •  after 1 Meiotic cycle,  for cells are produced with half the number of chromosomes as the parent chromosome


    How many mitotic divisions are required to produce 128 muscle cells from a single muscle cell? 

    2^n = 128


    Hence, 7 mitotic divisions are required 


    Why is the number of chromosomes in somatic cells different from gametes or sex cells?


    Autosomes or Somatic cells have 46 chromosomes since mitosis cell division takes place in these cells and the chromosomes also divide in number giving each daughter cell the same number of chromosomes as the parent cell.

    In Germ cells or Sex cells or Gametes, “Reduction Division” takes place during the first phase of meiotic cell division and the number of chromosomes are halved. In the second phase “Equational Division” takes place and two more daughter cells are produced with the same number of chromosomes as in the “reduction phase”.


    How does the cell prepare for the cell division process just before Mitosis or Meiosis?

    Just before mitosis or meiosis, the cell is in the “Interphase” stage and performs the following functions:

    • Growth

    • DNA Replication

    • Cell Functions


    What are chromatids?

    Chromatids are the strands of replicated chromosomes with a centromere. You can call it the arm of the chromosome. There may be 1 or 2 chromatids in a chromosome depending on whether it is haploid or diploid.


    What is centromere?

    Centromere is that part of the chromosome which holds the sister chromatids together. We decide the number of chromosomes based on the number of centromeres in the chromosomes. 


    How is Meiosis different from Fertilization?

    • Meiosis is the process of cell division of gametes whereas fertilization is the process of fusion of gametes.

    • Meiosis Ensures production of haploid phase (23 chromosomes in sperm and 23 chromosomes in ovum) in the life cycle of sexually  reproducing organisms  whereas fertilization restores the diploid phase (46 chromosomes in fertilized cell or zygote)


    What is meant by homologous chromosomes?

    The chromosomes which are approximately the same length in size and contain the same type of genes at the same location are called homologous chromosomes. The position of the central is the same for both the chromosomes.


    When the process of cell division begins in gametes,  the chromosomes start thickening and line up with their homologous pair. E.g. chromosomes with genes for eye colour at the same location will come side by side. Since the positions of similar genes are the same, they are going to match up. In this set,  one committed comes from the male didn't and the other from the female period.


    What is meant by crossing-over in Meiosis?

    Crossing over or re- combination means exchange of chromosome segments between non-sister chromatids during the production of gametes.

    Crossing-over provides variation amongst siblings.


    What is meant by independent assortment?

    Independent assortment means different genes independently separate from one another when reproductive daughter cells develop from the parent cell.


    Why do siblings not appear the same in physical appearance?

    Same mom, same father but siblings have different this is due to the crossing over and independent assortment of genes during meiosis phase of cell division of gametes. These two factors bring variety. 


    What is meant by non-disjunction of Genes?

    When chromosomes don't separate correctly, the sister chromatids are conjoined so the daughter cells may receive many or too few chromosomes causing genetic disorder.


    What is the role of centrioles during cell division?

    Central help in spindle formation to move the replicated chromosomes away from the center and towards the equator of the cell.

    Comment on the statement-meiosis enables the conservation of specific chromosome number of each species even though the process per se results in reduction of chromosome number.

    Meiosis produces daughter cells with half the number of chromosome so that when they can eat fertilizers the total number of chromosomes in the cell are restore to 46


    Male Gamete + Female Gamete = Fertilized Cell  or Zygote

    (23 chromosomes) (23 chromosomes) (46 chromosomes)

    A cell divides every one minute.  At this rate, it can fill a 100 ml of beaker in one hour.  How much time does it take to fill 

     a) 50 ml of beaker 

     b) 25 ml of beaker ?


    Ans: a) 59 min b) 58 min

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    Cell Division - Mitosis and Meiosis (Basic concepts)

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Material : CBSE - Class 8 - Biology

Topic : NCERT - Biology

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