SELINA Solutions for Class 10 Biology Chapter 2 - Structure of Chromosomes, Cell Cycle and Cell Division

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Chapter 2 - Structure of Chromosomes, Cell Cycle and Cell Division Exercise Ex. 1

Question A.1

The chromatin material is formed of

(a) DNA only

(b) DNA and Histones

(c) Histones only

(d) Nucleotides

Solution A.1

(b) DNA and Histones

Question A.2

The term “chromosomes” literally means

(a) Inherited bodies

(b) Twisted threads

(c) Coloured bodies

(d) Shining threads

Solution A.2

(c) Coloured bodies

Question A.3

The number of chromosomes in a certain type of cell division is halved. This kind of cell division occurs in

(a) only testis

(b) only ovary

(c) both ovary and testis

(d) all body cells

Solution A.3

(c) both ovary and testis

Question A.4

In which one of the following options the two stages of mitosis have been given in correct sequence?

(a) Prophase, metaphase, telophase, anaphase

(b) Prophase, metaphase, anaphase, telophase

(c) Anaphase, telophase,  prophase, metaphase

(d) Telophase, anaphase, prophase, metaphase

Solution A.4

(c) Anaphase, telophase,  prophase, metaphase

Question A.5

Synthesis phase in the cell cycle is called so for the synthesis of more of

(a) RNA

(b) RNA and proteins

(c) DNA

(d) Glucose

Solution A.5

(c) DNA

Question B.1

Name the following:

(a) The repeating components of each DNA strand lengthwise.

(b) The complex structure consisting of DNA strand and a core of histones.

(c) The type of bond which joins the complementary nitrogenous bases.

(d) The three components of nucleotide.

Solution B.1

(a) - Nucleotides.

(b) - Nucleosome.

(c) - Hydrogen Bond.

(d) - Phosphate, Sugar and Nitrogenous base.

Question B.2

Imagine one cell (A) has undergone one mitotic division and another cell (B) has completed its meiotic division. How many cells would the two produce?

Cell A: ............................

Cell B:.............................

Solution B.2

Cell A: 2

Cell B: 4

Question B.3

Column 'A'

Column 'B'

(a) Chromosomes become arranged in a horizontal plane at the equator.

(b) Daughter chromosomes move to the opposite poles of a spindle

(c) Chromosomes become visible as fine long threads.

(d) Chromosomes lose their distinctiveness and gradually become transformed into a chromatin network

Anaphase

 

 

Prophase

 

 

Telophase

 

Metaphase

Solution B.3

(a) - Metaphase.

(b) - Telophase.

(c) - Prophase.

(d) - Anaphase.

Question B.4

Fill in the blanks.

(a) DNA replicates in the ............. of the cell cycle.  

(b) Mitosis occurs in our ............. cells.

(c) Meiosis occurs only in ............. cells.

(d) Modern humans have 46 chromosomes. Their sperms and eggs will have .......... chromosomes each.

(e) During the pairing of chromosomes in meiosis, the ............ chromosomes come to lie side by side.

(f) The two non-sister chromatids of a paired chromosome are attached to each other at .......... during the process of crossing over.

Solution B.4

(a) DNA replicates in the synthesis (S) phase of the cell cycle.  

(b) Mitosis occurs in our somatic (body) cells.

(c) Meiosis occurs only in reproductive cells.

(d) Modern humans have 46 chromosomes. Their sperms and eggs will have 23 chromosomes each.

(e) During the pairing of chromosomes in meiosis, the homologous chromosomes come to lie side by side.

(f) The two non-sister chromatids of a paired chromosome are attached to each other at chaisma during the process of crossing over.

Question C.1

What is the difference between chromatin fibre and chromosome?

Solution C.1

Chromatin fibre is unfolded, uncondensed, extended DNA. It is only visible when cell under goes division whereas chromosomes are condensed DNA and they are visible when the cell is divided.

Question C.2

What are the rungs of the "DNA ladder" made of?

Solution C.2

Rungs of DNA ladder is made of nitrogenous bases which includes Adenine (A), Guanine (G), Cytosine (C) and Thymine (T).

Question C.3

Correct the following statements if there is any mistake.

(a) The four nitrogenous bases in the DNA are Guanine, Thiamine, Adrenaline and Cytosine.

(b) Genes are specific sequences of bases on a chromosome.

(c) A nucleotide is composed of a sulphate, a sugar (pentose) and a nitrogenous base.

(d) Nucleosomes are groups of cysteine molecules surrounded by DNA strands.

(e) If there are 46 chromosomes in a cell there will be 23 chromatin fibres inside the nucleus during interphase.

Solution C.3

(a) The four nitrogenous bases in the DNA ladder are Guanine, Thymine, Adenine and Cytosine.

(b) Genes are specific sequences of nucleotides on a chromosome.

(c) A nucleotide is composed of a phosphate, sugar (pentose) and a nitrogenous base.

(d) Nucleosomes are groups of histone molecules surrounded by DNA strands.

(e) If there are 46 chromosomes in a cell there will be 46 chromatin fibres inside the nucleus during interphase.

Question D.1

Mention whether the following statements are true (T) or false (F). Give reason in support of your answer.

 

(a) As you grow from childhood to adult hood, your skin cells divide only to replace such cells that are lost from the surface.

(b) Nuclear membrane in a mitotically dividing cell remains intact up to the metaphase and disappears only in the telophase.

(c) Mitotic cell division can be a mode of reproduction.

(d) Crossing-over between chromatids can occur only between homologous chromosomes.

Solution D.1

(a) False (F); Surface skin cells are continuously lost and replaced by the underlying cells.

(b) False (F); Nuclear membrane disappears in Prophase itself, however it reappears during Telophase.

(c) True (T); Mitotic cell division can be a mode of asexual reproduction in unicellular organisms like amoeba or yeast cell which divides into two daughter cells.

(d) True (T); While the maternal and paternal chromosomes are separating, the chromatid material gets exchanged between the two members of a homologous pair resulting in genetic recombination.

Question D.2

Define the following terms:

(a) Chromosome

(b) Gene

(c) Cell division

(d) Chromatid

(e) Aster

Solution D.2

(a) Chromosome: Chromosomes are highly condensed coiled chromatin fibres made of DNA which carry the hereditary material of the organisms.

(b) Gene: Genes are specific sequences of nucleotides on a chromosome that encode particular proteins which express in the form of some particular feature of the body.

(c) Cell division: Cell division is the method in which the cell divides and the duplicated chromosomes get evenly distributed into the daughter cells.

(d) Chromatid: Duplicated chromosomes consist of two identical strands, each of these is called a chromatid.

(e) Aster: Each centriole is surrounded by radiating rays and is termed aster.

Question D.3

Give reason:

(a) Gametes must be produced by meiosis for sexual reproduction.

(b) Why is meiosis referred to as 'reductional division'?

(c) The children of the same parents, howsoever similar, are different from each other in certain aspects.

Solution D.3

(a) Gametes must be produced by meiosis for sexual reproduction because the numbers of chromosomes are reduced to half during meiosis and then the normal diploid numbers of chromosomes are regained during the process of fertilization.

(b) Meiosis is referred to as 'reductional division' because the number of chromosomes are reduced to half i.e. out of the 23 pairs of chromosomes in humans, only single set of chromosomes are passed on to the sex cells.

(c) The mixing up or recombination of genes during meiotic division provides for the innumerable variations and diversity in the progeny. That is how, the children of the same parents, howsoever similar, are different from each other in certain aspects.

Question D.4

Distinguish between the following pairs:

(a) Cytokinesis and Karyokinesis

(b) DNA and RNA

(c) Nucleosome and Nucleotide

(d) Centrosome and Centromere

(e) Haploid and Diploid

Solution D.4

(a) Differences between cytokinesis and karyokinesis:

Cytokinesis

Karyokinesis

1. It is the division of the cytoplasm.

1. It is the division of the nucleus.

2. It occurs after karyokinesis.

2. It is the first division.

3. It results in the formation of two daughter cells.

3. It results in the formation of two nuclei.

 

(b) Differences between DNA and RNA:

DNA

RNA

1. DNA is deoxyribonucleic acid.

1. RNA is ribonucleic acid.

2. It consists of four distinct bases: thymine, adenine, cytosine and guanine.

2. It consists of four distinct bases: uracil, adenine, cytosine and guanine.

3. It is located in the nucleus of a cell and in the mitochondria.

3. It is found in the cytoplasm, nucleus, and in the ribosome.

4. The DNA is a double-stranded molecule.

4. The RNA is a single-stranded molecule.

 

(c) Differences between nucleosome and nucleotide:

Nucleosome

Nucleotide

It is the complex that it is made up of DNA wrapped around histone proteins.

The chemical composition of nucleotide consists of a phosphate group, a sugar and a nitrogenous base.

 

(d) Differences between centrosome and centromere:

Centrosome

Centromere

1. It is an organelle of the animal cell.

1. It is a non-stainable part of chromo-some at which two chromatids join.

2. It contains two centrioles which move towards the opposite poles and forms spindle fibres during cell division.

2. It provides attachment of spindle fibres during cell division.

 

(e) Differences between haploid and diploid:

Haploid

Diploid

1. It is a state of half the number of chromosomes than the original.

1. It is a state of full set of chromosomes.

2. It is denoted by n.

2. It is denoted by 2n.

3. This state is found during meiotic division.

3. This state is found during mitotic division.

 

Question D.5

Enumerate the various changes that occur in the nucleus of the cell during (a) prophase (b) anaphase of mitotic division. 

Solution D.5

Changes which occur in the nucleus of the cell during mitosis:

During prophase:

 The nuclear membrane and the nucleolus disappear.

 The duplicated chromosomes begin to move towards the equator of the cell.

During anaphase:

 The two sister chromatids of each chromosome separate and are drawn apart towards the opposite poles.

Question D.6

Name and explain the various stages of the cell cycle.

Solution D.6

Stages of the cell cycle:

 Non-dividing interphase

 Dividing mitotic phase or M phase

Interphase:

In interphase, cells grow in size and volume and prepare for the next cell division.

It is divided into three phases:

 First growth phase (G1): RNA and proteins are synthesised, and the volume of the cytoplasm increases.

 Synthesis phase (S): DNA is synthesised and chromosomes are duplicated.

 Second growth phase (G2): RNA and proteins continue to be synthesised.

Mitosis:

Mitosis is the division of somatic cells in which two identical daughter cells are produced by the division of one parent cell.

It consists of the following phases:

 Karyokinesis: It is the division of the nucleus during cell division.

 Cytokinesis: It is the division of the cytoplasm during cell division.

Karyokinesis:

It occurs in four phases:

 Prophase: During prophase, chromatin fibres condense and thick chromosomes are visible. The nucleolus and nuclear membrane disappear. A pair of centrioles duplicates. The spindle apparatus starts forming.

 Metaphase: Chromosomes are arranged on the metaphase plate or equatorial plane.

 Anaphase: The centromere divides, and the sister chromatids separate from each other. Spindle fibres contract and pull chromatids towards opposite poles.

 Telophase: Spindle apparatus disappears. Chromosomes become thin and turn into chromatin fibres. Nuclear membranes and nucleoli reappear.

Cytokinesis:

 The furrow continues to deepen in the cell, and it finally divides the cytoplasm forming two new daughter cells.

 In plant cells, a cell plate appears at the equatorial plane.

Question E.1

Given below is a schematic diagram of a portion of DNA.

Selina Solutions Icse Class 10 Biology Chapter - Structure Of Chromosomes Cell Cycle And Cell Division

(a) How many strands are shown in the diagram?

(b) How many nucleotides have been shown in each strand?

(c) Name the parts numbered 1,2,3,4 and 5 respectively.

(d) Name the DNA unit constituted by the parts 1, 2 and 3 collectively.

Solution E.1

(a) 2

(b) 2 on each strand

(c) 1- Phosphate,2- Sugar, 3- Bases,4- Hydrogen Bond,5 - Base

(d)Nucleotide

Question E.2

The three sketches given below (A, B and C) are intended to represent the replication of DNA. What should be their correct sequence starting with the first and ending with the last? ...........

Selina Solutions Icse Class 10 Biology Chapter - Structure Of Chromosomes Cell Cycle And Cell Division

Solution E.2

B, C and A.

Question E.3

The diagram below represents a stage during cell division. Study the same and then answer the questions that follow:

Selina Solutions Icse Class 10 Biology Chapter - Structure Of Chromosomes Cell Cycle And Cell Division 

a. Name the parts labelled 1, 2 and 3.

b. Identify the above stage and give a reason to support your answer.

c. Mention where in the body this type of cell division occurs.

d. Name the stage prior to this stage and draw a diagram to represent the same.

Solution E.3

a.  

1 - Centromere

2 - Spindle fibres

3 - Chromatids

 

b. The stage described in the diagram is the late anaphase of mitosis in an animal cell. The stage can be identified by the presence of separated chromatids which are found at the two poles of the cell. The appearance of the furrow in the cell membrane classifies the stage as the late anaphase.

 

c. The division is mitotic division and this kind of cell division occurs in all the cells of the body except for the reproductive cells.

 

d. The stage before anaphase is metaphase.

Selina Solutions Icse Class 10 Biology Chapter - Structure Of Chromosomes Cell Cycle And Cell Division 

Question E.4

Draw a labelled diagram to show the metaphase stage of mitosis in an animal cell having '6' chromosomes.

Solution E.4

Selina Solutions Icse Class 10 Biology Chapter - Structure Of Chromosomes Cell Cycle And Cell Division

Question E.5

The diagram given below represents a certain phenomenon which occurs during meiosis.

Selina Solutions Icse Class 10 Biology Chapter - Structure Of Chromosomes Cell Cycle And Cell Division

Name and explain the phenomenon by using the terms - homologous chromosomes, chromatids, and crossing-over.

Solution E.5

The exchange of chromatids between homologous chromosomes is called crossing-over. This is the process by which the two chromosomes of a homologous pair exchange equal segments with each other.

Crossing over occurs in the first division of meiosis. At that stage each chromosome has replicated into two strands called sister chromatids. The two homologous chromosomes of a pair synapse, or come together. While the chromosomes are synapsed, breaks occur at corresponding points in two of the non-sister chromatids, i.e., in one chromatid of each chromosome.

Since the chromosomes are homologous, breaks at corresponding points mean that the segments that are broken off contain corresponding genes, i.e., alleles. The broken sections are then exchanged between the chromosomes to form complete new units, and each new recombined chromosome of the pair can go to a different daughter sex cell. It results in recombination of genes found on the same chromosome, called linked genes that would otherwise always be transmitted together.

Question E.6

Given below is a diagram representing a stage during mitotic cell division in an animal cell. Examine it carefully and answer the questions which follow.

Selina Solutions Icse Class 10 Biology Chapter - Structure Of Chromosomes Cell Cycle And Cell Division

(a)Identify the stage. Give one reason in support of your answer.

(b) Name the cell organelle that forms the 'aster'.

(c) Name the parts labelled 1, 2 and 3.

(d) Name the stage that follows the one shown here. How is that stage identified?

(e) Mention two points of difference between mitosis and meiosis with regard to:

(i) The number of daughter cells produced.

(ii)The chromosome number in the daughter cells.

Solution E.6

(a) Late prophase. Because the nuclear membrane and nucleolus have disappeared.

(b) Centrioles.

(c) 1 - Centromere

2 - Chromatids.

3 - Spindle fibre.

(d) Metaphase. The centromeres of chromosomes are drawn to the equator by equal pull of two chromosomal spindle fibres that connects each centromere to the opposite poles, forming a metaphasic plate.

(e)

Mitosis

Meiosis

(i) Two daughter cells are produced.

(i) Four daughter cells are produced.

(ii) It is equational division i.e. the number of chromosome in the daughter cells or parent cells remains the same.

(ii) It is reductional division i.e. the number of chromosomes is reduced to half in the daughter cells.

Question E.7

Given ahead are three diagrammatic sketches (A, B and C) of one and the same particular phase during mitotic type of cell division.

Selina Solutions Icse Class 10 Biology Chapter - Structure Of Chromosomes Cell Cycle And Cell Division

(a) Identify the phase ..............

(b) What is the diploid number of chromosomes shown in them? ................

(c) Identify whether these are animal cells or plant cell? Give reasons.

A .................

B .................

C .................

Solution E.7

(a) Metaphase.

(b) 4.

(c) A - Animal

B - Animal

C - Plant

Question E.8

Shown below are four stages (A, B, C, D) (not in sequence) of a certain kind of cell division.

Selina Solutions Icse Class 10 Biology Chapter - Structure Of Chromosomes Cell Cycle And Cell Division

(a) Is it a plant cell or an animal cell? Give two reasons .............

(b) Is it undergoing mitosis or meiosis? ..................

(c) What should be the correct sequence of these four stages among themselves? ..................

(d) Name the stage that should precede the earliest of these stages..............

(e) Draw the stage named above inside the blank space provided.

Solution E.8

(a) This is an animal cell because:

(i) The outline is circular (in plants it would be angular {rectangular or polygonal}) and cell wall is absent.

(ii) Centrosomes on centrioles are present. (These are found only in animal cells)

(b) Mitosis.

(c) B, C, D, A.

(d) Interphase.

(e)

Selina Solutions Icse Class 10 Biology Chapter - Structure Of Chromosomes Cell Cycle And Cell Division

Question E.9

Given below is a diagram representing a stage during mitotic cell division. Study it carefully and answer the questions that follow.

Selina Solutions Icse Class 10 Biology Chapter - Structure Of Chromosomes Cell Cycle And Cell Division 

 

(a) Is it a plant cell or an animal cell? Give a reason to support your answer.

(b) Identify the stage shown.

(c) Name the stage that follows the one shown here. How is that stage identified?

(d) How will you differentiate between mitosis and meiosis on the basis of the chromosome number in the daughter cells?

(e) Draw a duplicated chromosome and label its parts.

Solution E.9

(a) It is a plant cell because centrioles are not shown in the diagram.

(b) Prophase

(c) Metaphase. Chromosomes arrange themselves on the metaphase or equatorial plate.

(d) Difference between mitosis and meiosis based on the chromosome number in daughter cells: 

Mitosis

Meiosis

Chromosome number remains the same as that of parent cells.

Daughter cells receive only half the number of chromosomes from parent cells.

 

(e) Duplicated chromosome:

Selina Solutions Icse Class 10 Biology Chapter - Structure Of Chromosomes Cell Cycle And Cell Division