1.  Differences between Mitosis and Meiosis.

 Mitosis :

(i)  Mitosis takes place within somatic cells (cells that make up the body)

(ii)  One single division of the mother cell, results in two daughter cells

(iii)  A mitotic mother cell can either be haploid or diploid

(iv)  The number of chromosomes per nucleus remain the same after division.

(v)  It is preceded by the S-phase in which the amount of DNA is duplicated.

(vi)  In mitosis, there is no pairing of homologous chromosomes.

(vii)  There is no exchange of DNA (crossing-over) between chromosomes.

(viii)  The centromeres split during anaphase.

(ix)  The genotype of the daughter cells is identical to that of the mother cells.

(x)  Cytokinesis follows karyokinesis.

   Meiosis :

(i)  Meiosis takes place within gametic cells (reproductive cells)

(ii)  Two divisions of the mother cell, result in four meiotic products or haploid gametes. 

(iii)  A meiotic mother cell is always diploid.

(iv)  The meiotic products contain a haploid (n) number of chromosomes in contrast to the diploid (2n) number of chromosomes in mother cell.

(v)  In meiosis, only meiosis I is preceded by S-phase.

(vi)  During prophase I, complete pairing of all homologous chromosomes takes place.

(vii)  There is at least one cross-over or DNA exchange, per homologous pair of chromosomes.

(viii)  The centromeres get separated during anaphase II, but not during anaphase I.

(ix)  Meiotic products differ in their genotype from the mother cell.

(x)  Cytokinesis occurs after both meiosis I and meiosis II

 2.  At what phase of cell division do the following occur?

(i)  Development of spindle.

(ii)  Separation of sister chromatids.

(iii)  Reappearance of nuclear membrane.

(iv)  Condensation of chromatin into typical chromosomes

(i)  Metaphase   (ii)  Anaphase    (iii)  Telophase     (iv)  Metaphase

3.  List the basic needs of cell division in organisms

Cell division takes place for the following needs :

(i)  Mitosis is important for the growth of cells.

(ii)  Reproduction requires gamete production (sperm, ova, pollengrains, eggs) which is done by meiosis.

4.  Name the type of cell division that occurs during :

(i)  growth of shoot.    (ii) formation of pollen grains   (iii) repair of worn out tissues

(i)  Mitosis   (ii)  Meiosis    (iii)  Mitosis

 5.  What is the main significance of mitosis?

Mitosis helps in duplication of cells for growth and repair of the body.

6.  What is the main significance of meiosis?

Meiosis helps in the formation of gametes-sperms and ova-for sexual reproduction.

7.  Define the following terms

      (i)  Cell        (ii)  Cell organelle        (iii)  Mitosis       (iv)  Interphase

 (i)  Cell :  The smallest, microscopic structural and functional unit of living organisms.

 (ii)  Cell Organelle :  The membrane-bound, specialised structures present in the cytoplasm that perform specific functions of the cell.

  (iii)   Mitosis :  Mitosis is the process of cell division, by which new cells are generated with the same genetic component as the parent cell.  It is an equational divisioin occuring in somatic cells of the body.

  (iv)  Interphase :  is the period between two cell divisions in which the nuclear envelope is intact and chromosomes are not apparent.

8.  What are homologous chromosome?

 A pair of paternal and maternal chromosomes having similar form size and structure.

9.  "First meiotic division is the reduction division."  What does the word reduction refer to in this statement?

Reduction refers to the halving of the chromosome number from the parent cell in meiosis I.  For example, in humans, at the end of meiosis I, the chromosome number is reduced to 23 from 46.

10.  What is the significance of mitosis?

(i)  Growth :  The cells within an organism divide to produce identical replicas of itself with the same number of genes and chromosomes both in animals and plants.

(ii)  Cell Replacements :  Cells constantly die and are replaced by new ones in the body.  For example, old blood cells are replaced by new blood cells when they die.

(iii)  Repair and Regeneration :   Some animals can regenerate parts of the body by mitosis eg: lizards regenerate their tails.  The damaged tissues are repaired, and normal functioning of the cells is retained.

(iv)  Vegetative or Asexual Reproduction :  Single celled organisms and plants, produce offspring which are genetically similar to themsleves, by mitosis.

(v)  Continuity of Genetic Material :  It ensures that the two daughter cells inherit the same number of chromososmes, and hence the same characteristics as the parent cell.

11.  What is the significance or meiosis ?

(i)  It reduces the number of sets of chromosomes by half, so that when gametic recombination occurs (fertilization), the ploidy of the parents will be reestablished.

(ii)  Meiosis helps in the formation of male and female gametes called sperms and ova respectively, in sexual reproduction only.

(iii)  The shuffling of the genetic material produce genetically unique gametes, each of which can fuse with another unique gamete, during fertilization, to produce a unique zygote of the next generation, having a genome quite different from that of either parent.

(iv)  It causes variation by crossing over and chiasmata formation between homologous chromosomes.

(v)  Variations produced during meiosis are one of the causes of evolution.

 12.  Answer the following :

(i)  What is the division of nucleus called?

(ii)  Why do chromosomes always occur in even number?

(iii)  What is cytokinesis?

(iv)  Why is meiosis known as the reductional division?

(v)  Why is meiosis II known as the equatorial division?

(i)  The division of nucleus is called karyokinesis.

(ii)  The chromosomes always occur in even numbers because they are always in pairs.

(iii)  The division of cytoplasm and its contents into two equal halves is known as cytokinesis.

(iv)  As the number of chromosomes reduce to half, during the meiotic division therefore, it is known as reductional division.

(v)  Since the number of chromosomes remain same at the end of meiosis II, it is known as equatorial divison.

13.  (i)  Define Mitosis

(ii)  What do you mean by karyokinesis?

(iii)  What is the period between the two cell divisions called?

(iv)  How many daughter cells are produced at the end of meiosis?

(i)  Mitosis is a type of cell division by which two daughter cells are generated with the same genetic composition as the parent cell.

(ii)  During the cell division the nucleus divides into two equal halves, which are identical.  This division is called karyokinesis.

(iii)  The period between two cell divisions is called interphase.

(iv)  Four daughter cells are produced at the end of meiosis

14.  (i)  Explain what do you mean by the words 'haploid' and 'diploid' in the cell division.

(i)  The number of complete sets of chromosomes in a cell is called ploidy.  Diploid (indicated by 2n) cells have two homologous copies of chromosome, one from each parent.  Most of the somatic cells are diploid, but sex cells are always haploid.  The haploid number is half the total number of chromosomes in a somatic cell of an individual.  It is denoted by 'n'.  The gametes are always haploid.

15.  (i)  Why do chromosomes always occur in even numbers?

(ii)  What is the process called by which cells multiply?

(iii)  What do you mean by meiosis?

(iv)  Define amitosis

(v)  How does cytokinesis in plant cells differ from that in animal cells?

(i)  The chromosomes always occur in even numbers because they are always in pairs.

(ii)  The process by which cells multiply is called cell division.

(iii)  It is  a type of cell division that gives rise to four daughter cells each having half the chromosome number (n) as that of the parent.

(iv)  The simple common process of cell division which does not have any substages occuring in the prokaryotic cells is called amitosis.

(v)  In plant cells, cytokinesis occurs with the formation of cell plate in the centre by dictyosomes and endoplasmic reticulum.  In animal cells, cytokinesis starts with the formation of a furrow in the cell membrane at the equatorial plane.

17.Give the significance of mitosis and meiosis.

Significance of Mitosis

(i)  Growth :  The cells within an organism divide to produce identical replicas of itself with the same number of genes and chromosomes both in animals and plants.

(ii)  Cell Replacements :  Cells constantly die and are replaced by new ones in the body.  For example, old blood cells are replaced by new blood cells when they die.

(iii)  Repair and Regeneration:  Some animals can regenerate parts of the body by mitosis, example: lizards regenerate their tails.  The damaged tissues are repaired, and normal functioning of the cells is retained.

(iv)  Vegetative or Asexual Reproduction :  Single celled organism and plants, produce offspring which are genetically similar to themsleves, by mitosis.

(v)  Continuity of Genetic Material :  It ensures that the two daughter cells inherit the same number of chromosomes, and hence the same characteristics as the parent cell.

Significance of Meiosis

(i)  It reduces the number of sets of chromosomes by half, so that when gametic recombination occurs (fertilisation), the ploidy of the parents will be re-established

(ii)  Meiosis helps in the formation of male and female gametes called sperms and ova respectively, in sexual reproduction only.

(iii)  The shuffling of the genetic material produces genetically unique gametes, each of which can fuse with another unique gamete, during fertilisation, to produce a unique zygote of the next generation, having a genome quite different from that of either parent.

(iv)  It causes variations by crossing over and chiasmata formation between homologous chromosomes.

(v)  Variations produced during meiosis are one of the causes of evolution.

18.  (i)  What is interphase?

(ii)  Mention three significant activities that occur in interphase.

(iii)  What is cytokinesis?

(i)  Interphase is the period between two cell divisions in which the nuclear envelope is intact and chromosomes are not apparent.

(ii)  Interphase is a stage of the cell preparing for the cell divisions.  The changes occuring during interphase are : synthesis of RNA and protein , and cell growth.

(iii)  Cytokinesis is the division of the cytoplasm into two identical halves.  It begins during anaphase or telophase depending on the cell type.

19.  Define the following terms :

(i)  Karyokinesis   (ii)  Cytokinesis    (iii)  Diploid       (iv)  Crossing over.

(i)   Karyokinesis is the division of the nucleus (genetic material) into two identical halves.  It occurs well before cytokinesis.

(ii)  Cytokinesis is the division of the cytoplasm into two identical halves.  It begins during anaphase or telophase depending on the cell type.

(iii)  A cell or organism having double sets of unpaired chromosomes is called diploid.

(iv)  The mutual exchange of genetic material between the corresponding homologus chromosomes during prophase I of meiosis is called crossing over.

20.  Explain the following

(i)  Mitotic cell divsion   

 (i)  Mitosis is the process of cell division, by which new cells are generated with the same genetic component as the parent cell.  It is an equatiorial division occuring in somatic cells of the body.

Mitosis is divided into four stages: prophase, metaphase, anaphase and telophase.

Prophase.  It is recognised by the following features:

(i)  There occurs the condensation of thin threads of chromatic into chromosomes and the chromosomes become shorter and thicker, so that individual chromosomes become recognisable.

(ii)  In animal cells, the two centrioles of the centrosome separate and move to opposite poles.  These are absent in plant cells.

(iii)  Towards the end of prophase nuclear membrane disappears.

Metaphase  The chromosomes are most condensed and appeat as typical chromosomes.  They lie at the metaphase plate held by spindle fibres.

Anaphase  The chromosomes split at centromeres and daughter chromosomes move towards opposite poles due to spindle fibres

Telophase  The chromosomes reach the opposite poles, uncoil and nuclear membrane is reformed.              

21.  (i)  What is a prokaryotic cell?

(ii)  What is a eukaryotic cell?

(i)  Prokaryotic cells are the first living organisms, primarily distinguished by the absence of a membrane-bound nucleus.  They are enclosed in a plasma membrane and contain the genetic material within the cytoplasm.  Ribosomes are the only type of organelles present, they lack fully developed cell organelles example: bacteria and blue-green algae.

(ii)  Eukaryotic cells are evolved from the prokaryote-like ancestor.  They are complex, distinguished by a membrane-bound nucleus and contain membrane bound structures called organelles such as mitochondria and chloroplasts.  These type of cells are found in most of the plants and animals.

22.  Distinguish between mitotic cell division in plant cell and animal cells.

Plant cell

(a)  Centriole absent at spindle poles.

(b)  No asters are formed (anastral)

(c)  Cell plate grows centrufugally

(d)  Occurs mainly at meristems.

Animal cell

(a)  Centrioles present at spindle poles.

(b)  Asters are formed (amphiastral)

(c)  Furrow extends centripetally

(d)  Occurs nearly in all tissues

23.  Give one point of difference between karyokinesis and cytokinesis

Karyokinesis is the division of the nucleus into two daughter nuclei while cytokinesis is the division of the cytoplasm between two daughter cells.

24.  Identify and name the following terms from the statements given below:

(i)  Chromosomes appear threadlike.

(ii)  A pair of chromosomes carrying dissimilar alleles for a particular character.

 (i)  Chromatin

(ii)  Homologous chromosomes

25.  Give reasons as to why gametes have a haploid number of chromosomes.

During meiosis I., there occurs a reductional division followed by meiosis II in which equatiorial division occurs, resulting in the reduction of the chromosome number to half (haploid number).