108—113 · (15) ArunDeep’s Biology-10 Structure of Chromosomes, Cell Cycle and Cell Division PROGRESS CHECK Fill in the blanks. 1. ... (c)Chromosomes become visible as fine long

Unit 1 : Basic Biology

1. Cell-The Structure and Functional Unit of Life 1 — 14

Exercise 1—14

2. Structure of Chromosomes, Cell Cycle And Cell Division 15 — 30

Exercise 15—25

Solved Questions from Board Examination Papers 26 — 30

3. Genetics — Some Basic Fundamentals 31 — 43

Exercise 31—39

Solved Questions from Board Examination Papers 40—43

Unit 2 : Plant Physiology

4. Absorption by Roots — The Processes Involved 44 — 64

Exercise 44—59


5. Transpiration 65 — 83

Exercise 65—78


6. Photosynthesis 84 — 107

Exercise 84—96


Contents

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7. Chemical Coordination in Plants 108 — 113

Exercise 108—113

Unit-3 : Human Anatomy and Physiology

8. The Circulatory System 114 — 138

Exercise 114—131


9. Excretory System 139 — 153

Exercise 139—150


10. Nervous System 154—174

Exercise 154—162

11. Sense Organs 163—192

Exercise 163—174


12. The Endocrine System 193 — 211

Exercise 193—204


13. The Reproductive System 212—236

Exercise 212—226



Unit-4 : Human Evolution

14. Human Evolution 237—242

Exercise 237—242

Unit-5 : Population

15. Population — The Increasing Numbers and Rising Problems 243—252

Exercise 243—249


Unit-6 : Pollution

16.Pollution — A Rising Environmental Problem 253—258

Exercise 253—258

MULTIPLE CHOICE TYPE QUESTIONS 259 — 297

ICSE EXAMINATION PAPER SOLVED–2004 298 — 307







(15) ArunDeep’s Biology-10

Structure of Chromosomes,

Cell Cycle and Cell DivisionPROGRESS CHECK

Fill in the blanks.

1. Chromatin fibre is made up of DNA and ....................... .Ans. Histones2. The two sister chromatids of a chromosome are attached to each other at ............... .Ans. Centromere3. The structure of DNA was first discovered by .............. .Ans. Watson and Crick4. The three components of a nucleotide are .............., .............. and ..............Ans. phosphate, sugar and nitrogenous base.5. DNA strand wound around a histone octamer forms a complex called a ..............Ans. neucleosome6. A specific sequence of nucleotides on a chromosome constitutes a .............. .Ans. Genes.

Review Questions

A. Multiple Choice Type

(Choose the best option out of the four alternatives a, b, c and d)

1. The chromatin material is formed of

(a) DNA only (b) DNA and Histones (c) Histones only (d) Nucleotides

Ans. (b) DNA and Histones

2. The term “chromosomes” literally means

(a) Inherited bodies (b) Twisted threads (c) Coloured bodies (d) Shining threads

Ans. (c) Coloured bodies

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

(a) only testis (b) only ovary (c) both ovary and testis (d) all body cells

Ans. (c) both ovary and testis.

4. In which one of the following options the stages of mitosis have been given in correctsequence ?

(a) Prophase, metaphase, telophase, anaphase

(b) Prophase, metaphase, anaphase, telophase

(c) Anaphase, telophase, prophase, metaphase

(d) Telophase, anaphase, prophase, metaphase

Ans. (b) Prophase, metaphase, anaphase, telophase

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

Ans. (c) DNA

2



B. Very Short Answer Type

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 a nucleotide.

Ans. (a) nucleotides (b) nucleosome

(c) Hydrogen bond (d) phosphate, a sugar and nitrogenous base

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

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

Ans. Cell A : two Cell B : four (tetra)

3. Match the events given in column A with the phase in mitotic cell division in Column B.

Column ‘A’ Column ‘B’

(a) Chromosomes get arranged in a horizontal plane at the equator Anaphase

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

(c) Chromosomes become visible as fine long threads. Telophase

(d) Chromosomes lose their distinctiveness and gradually become Metaphase

transformed into a chromatin network.

Ans. (a) Metaphase (b) Anaphase (c) Prophase (d) Telophase

4. Fill in the blanks.

(a) DNA replicates in the .......... phase 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 lieside by side.

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

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

(b) Mitosis occurs in our somatic cells.

(c) Meiosis occurs only in reproductive cells.

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

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

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

C. SHORT ANSWER TYPE

Q.1. What is the difference between chromatin fibre and chromosome?



Ans.

Chromatin Fibres Chromosome

A network of very long extremely thin These are structure found in the

dark stained fibres inside the nucleus nucleus of a cell and are formed

made up of DNA threads. from chromatin. Chromosomes arethe carriers of genes.

Q.2. What are the rungs of the “DNA ladder” made of ?

Ans. The rungs of the “DNA ladder” are made of nitrogenous bases. They are G (Guanine), T(Thymine), A (Adenine) and C (Cytosine).

Q.3. Correct the following statements for mistakes, if any.

(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 thenucleus during interphase.

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

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

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

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

(e) If there are 46 chromosomes in a cell there will be 92 chromatin fibres inside the nucleusduring interphase.

D. DESCRIPTIVE TYPE

Q.1. Mention whether the following statements are true (T) or false (F). Give reason in support ofyour answer.

(a) As you grow from childhood to adulthood, your skin cells divide only to replace suchcells that are lost from the surface. T/F

Ans. True; When we are adults, our cell population stays constant. The number of new cells producedequals the number of dying cells.

(b) Nuclear membrane in a mitotically dividing cell remains intact up to metaphase anddisappears only in the telophase. T/F

Ans. False - Nuclear membrane in a mitotically dividing cell remains intact up to metaphase anddisappears only in the prophase.

(c) Mitotic cell division can be a mode of reproduction. T/FAns. True; It is a mode of reproduction in some of unicellular organisms.(d) Crossing-over between chromatids can occur only between homologous chromosomes. T/F

Ans. True; During pairing, some chromatids of homologous chromosomes break and rejoin at pointsof intersection. It causes crossing over.

Q. 2. Define the following terms : (a) Chromosome (b) Gene (c) Cell division (d) Chromatid (e) Aster

Ans.(a) Chromosomes : A thread like structure of nucleic acids and protein found in the nucleusof the most living cells carrying genetic information.

Structure of Chromosome : The chromosome has the following structures :



(i) Chromatid : A chromosome consists of two symmetrical structures called chromatids.The chromatids are attached to each other by centromere.

Structure of a chromosome

(ii) Chromonema : A chromonema represents a chromatid in the early stages of condensation.The chromonemata form the gene-bearing portion of chromosome.

(iii) Chromomeres : The chromomeres are bead-like accumulations of chromatin material.Chromatin matter are regions of tightly folded DNA.

(iv) Centromere and kinetochore : The centromere lies within a thinner segment ofchromosome, the primary constriction. Centromeres are found to contain specific DNAsequences with special protein bound to them, forming a disc shaped structure kinetochore.Depending upon the position of centromere (a clear zone in the chromosome – whichdivides the chromosome into two parts, each part called chromosome arm), a chromosomemay have the following shapes –

(a) Telocentric : Rod-shaped, having centromere at the proximal end.(b) Acrocentric : Rod-shaped, having centromere at one end but slightly below the normal position.(c) Submetacentric : T-shaped or L-shaped, having centromere almost at the middle position.(d) Metacentric : ‘V’-shaped having the centromere at the centre and forming two equal arms.

(b) GeneAns. 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. They are units of hereditywhich are transferred from parents to offsprings and are responsible for some specificcharacteristics of the offspring.

— Genes control the characteristics of living organisms. — Genes are carried on the chromosome. — Genes are in pairs. — Genes controlling the same characteristics occupy identical positions on corresponding chromosomes.

Genes are inherited in pairs (one from each parent)(i) Dominant gene : In a paired set of genes, the gene with the greater influence in determining

physical characters.(ii) Recessive gene : In a paired set of genes, the gene that influences or determining physical

characteristics only when no dominant gene is present.



(c) Cell division is one of the most fundamental characteristics of life. This is the method whichenables life to perpetuate generation after generation.

(d) Chromatid : One of the two identical parts of a chromosome after its duplication. Duringcell division, two chromatids make up a chromosome.

(e) Aster : The centrosome (in animal cell) splits into two along with simultaneous duplication ofthe centrioles contained in it. The daughter centrioles move apart and occupy opposite “poles”of the cell. Each centriole is surrounded by radiating rays and is termed aster (aster : star).

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, howesoever similar, are different from each other in

certain aspects.Ans. (a) The usual purpose of meiosis is to form gametes-the sex cells that will fuse together to form

a new diploid individual.In all plants and animals the gametes are of different sizes. This is called heterogamy.Female gametes (ova or eggs in animals, ovules in plants) are produced in fairly small numbers.Human females for example release about 500 ova in a lifetime. They are the large gametes andtend to be stationary. They often contain food reserves (lipids, proteins, carbohydrates) tonourish the embryo after fertilisation.Male gametes are produced in very large numbers. Human males for example release about 100million sperm in one ejaculation. They are the smaller gametes.

(b) During the first meiotic division, the bonding between homologous chromosomes separates, butthe centromeres of duplicated chromosomes stay together. For each chromosome pair, the maternalchromosome will go to one pole and the paternal to the other. Because the orientation of each pair(relative to the spindle) is random, there is independent assortment of maternal and paternalchromosomes at this division. This gives each daughter cell one complete set of duplicated, butnot yet separated chromosomes, with each individual chromosome randomly derived from one ofthe parents, entirely independently of the parental origin of the other chromosomes. At this stage,the cells contain a haploid number of duplicated chromosomes whose sister chromatids have notyet separated. The second division then occurs without further DNA synthesis. The centromeresseparate in this division, generating a haploid number of chromosomes, each of which consists ofa single chromatid. The DNA content at this stage is one half that of a pre-replication diploid cell.

(c) The mixing up of genes during meiotic division provides for the innumerable variations in theprogeny. That is how the children of the same parents, howsoever similar, are different fromeach other in certain aspects.

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

Ans.(a) Karyokinesis Cytokinesis 1. It refers to division of nucleus. 1. It refers to division of cytoplasm. 2. It results in the formation of two nuclei. 2. It results in the formation of two daughter cells.(b)

Basis DNA RNA Type DNA (Deoxyribonucleic acid) RNA (Ribonucleic acid)



Definition It is a long polymer. It has a Is a polymer with a ribose anddeoxyribose and phosphate phosphate backbone with fourbackbone having four distinct varying bases: uracil, cytosine,bases: thymine, adenine, cytosine, adenine, and guanine.and guanine.

Location It is located in the nucleus of a cell It is found in the cytoplasm,and in the mitochondria. nucleus, and in the ribosome.

Sugar portion It has 2-deoxyribose. It has Ribose.Function DNA is functional is the transmission RNA is functional is the

of genetic information. It forms as transmission of the genetic codea media for long-term storage. that is necessary for the protein

creation from the nucleus to theribosome.

Predominant The DNA is a double-stranded The RNA is a single-strandedStructure molecule that has a long chain molecule which has a shorter

of nucleotides. chain of nucleotides.(c) Nucleosome : Nucleosome are the completes in which DNA wraps around a protein core of

eight histone molecules. Nucleosomes are 10 mm in diameter.Neucleotide : Neucleotides are dervied from a neucleoside by addition of a molecule of phosphoricacid. The phosphate molecule is linked with sugar molecule at carbon no. 5 or at carbon no. 3.

(d)

Chromosome Centromere

They are responsible for inheritance It is the region of attachment of the

of characters from parents to off-spring. sister chromatids and also the site of

Chromosome also help in cell division attachment to the spindle fibre.

and control various metabolic activities.

(e)

Haploid Diploid

(i) Half the number of chromosomes A full set of chromosomes.

than the original.

(ii) Denoted by n. Denoted by 2n.

(iii) Found during meiotic division Found during mitotic division.

Q.5. Enumerate the various changes that occur in the nucleus of the cell during (a) prophase(b) anaphase of mitotic division.

Ans. The changes that occur in the nucleus of the cell during

(a) Prophase : Chromosomes become visible, the nucleolus disappears, the mitotic spindleforms, and the nuclear envelope disappears.

(i) Chromosomes become more coiled and can be viewed under a light microscope.

(ii) Each duplicated chromosome is seen as a pair of sister chromatids joined by the duplicated butunseparated centromere.

(iii) The nucleolus disappears during prophase.

(iv) In the cytoplasm, the mitotic spindle, consisting of microtubules and other proteins, formsbetween the two pairs of centrioles as they migrate to opposite poles of the cell.

(v) The nuclear envelope disappears at the end of prophase. This signals the beginning of the



substage called prometaphase.

(b) Anaphase : Sister chromatids separate, and the now-daughter chromosomes move to oppositepoles of the cell.

(i) Anaphase begins when the duplicated centromeres of each pair of sister chromatids separate,and the now-daughter chromosomes begin moving toward opposite poles of the cell due to theaction of the spindle.

(ii) Depending where the centromere is located along the chromosome, a characteristic shapeappears during chromosome movement. The two shown above give V and J shapes.

(iii) At the end of anaphase, a complete set of chromosomes has assembled at each pole of the cell.

Q.6. Name and explain the various stages of the cell cycle.

Ans. The sequence of events including duplication of genome, synthesis of other cell constitutents,growth and division, that a cell undergoes from the time of its formation upto its divisioninto daughter cells is called cell cycle. A cell cycle consists of the following two phases.

(i) Interphase (non-dividing phase). (ii) Mitotic phase (dividing phase).

(i) Interphase : It is a non-dividing, preparatory phaseduring which a cell grows to its maximum size. It is agrowth phase between two successive divisions of acell. It is further divided into three sub-stages.

(a) G1-Phase (First growth phase or Post-mitotic

phase) : Synthesis of RNA and proteins with increasein number of cell organelles takes place.

(b) S-Phase (Synthetic phase) : Synthesis of DNA andduplication of chromosomes takes place.

(c) G2-Phase (Second growth phase or Pre-mitotic

phase) : Formation of RNA and proteins continues andcell prepares to undergo mitotic phase of cell cycle.

(ii) Mitotic phase : It is the dividing phase where nucleus and cytoplasm divide into two daughtercells. It is divided in two parts i.e., Karyokinesis – Division of nucleus and Cytokinesis – divisionof cytoplasm.

Karyokinesis is studied under four stages : Prophase, Metaphase, Anaphase and Telophase.

E. Structured/Application/Skill Type

Q.1. Given below is a schematic diagram of a portion of DNA.

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

Ans. Two parallel strands.

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

Ans. Two

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

Ans. (1) Phosphate (2) Sugar (3) Pyrimidines (4) Hydrogen Bond(5) Purines

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

Ans. Nucleotides.

Q.2. The three sketches given below (A, B and C) are intended to represent the replication of

G -PHASEINITIAL GROWTH ORPRE DNA SYNTHESIS

PHASE UPTO TENHOURS

1

S-PHASEDNA

SYNTHESISPHASE UPTO

EIGHT HOURS

G -PHASEPOST DNA

SYNTHESIS ORSECOND GROWTH

PHASE UPTO FIVE HOURS

2

M-PHASEONE HOUR

TELOPHASEANAPHASEMETAPHASEPROPHASE

MITOSIS

Cell Cycle



DNA. What should be their correct sequence starting with the first and ending with thelast ? ..............

Ans. B – C – A

Q.3. The diagram below represents a stage during cell division. Study the same and thenanswer the questions that follow :

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

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

(c) Mention the type of cells in our body where this type of cell division occurs.

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

Ans.

(a) 1. Aster 2. Spindle fibres3. Chromatids.

(b) Late anaphase, a furrow starting inthe cell membrane at the middle ofthe cell.

(c) Somatic cells / Body (vegetative) cells

(d) Metaphase.

Q. 4. Draw a labelled diagram to show the metaphase stage of mitosis in an animal cell having‘6’ chromosomes.

Ans. (i)



Q.5. The diagram given below represents a certain phenomenon which occurs during meiosis.Name and explain the phenomenon by using the terms — homologous chromosomes,chromatids, crossing-over.

Ans. During pairing, some chromatids of homologous chromosomes break and rejoin at point ofintersection which is called chaismata. This causes crossing-over with exchange of chromatidmaterial between chromosomes from the parents to produce new combination of genes.

Q. 6. Given below is a diagram representing a stage during mitotic cell division in an animalcell. Examine it carefully and answer the questions which follow.

Nuclear membranedisappears

Aster

1

2

3

(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 differences between mitosis and meiosis with regard to :

(i) The number of daughter cells produced.

(ii) The chromosome number in the daughter cells.

Ans. (a) Prophase — Nuclear membrane disappears.

(b) Centrosome

(c) 1. Centromere 2. Sister chromatids 3. Spindle fibres

(d) Metaphase — Chromosomes line up on equatorial plane.

(e) Mitosis. (i) Two daughter cells are found,

(ii) Same number of chromosomes as that of parent cell.

Meiosis. (i) Four daughter cells are formed.

(ii) Half the number of chromosomes as that of parent cell.



Q.7. Given ahead are three diagrammatic sketches (A, B and C) of one and the same particularphase during mitotic type of 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 cells ? Give reasons.

A ................, B ................, C ................,

(d) Which of these is/are shown in correct direction ? (Tick mark the correct answer).

(i) Only A (ii) Only B (iii) Only A and C (iv) All the three.

Ans. (a) Metaphase, (b) 2n = 4,

(c) (A) Animal cells, (B) Animals cells, Reason for part (A) (B) : Each chromosome getsattached to spindle by its centromere. (C) Plants cells, Reason : Chromosomes line up in oneplane at equator. (d) (ii) only B.

Q.8. Shown below are four of the stages (A, B, C, D) (not in sequence) of a certain kind of celldivision.

(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.

Ans. (a) It is an animal cell because of the

presence of star like figure known

as aster which is not found in plant cell.

(b) It is undergoing Mitosis

(c) B C D AA

(d) Interphase (e) Fig. Interphase



Q.9. Given below is a diagram representing a stage during mitotic cell division. Study it

carefully and answer the questions that follow :

(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. (2014)

Ans. (a) Plant cell. Because Cell wall present and Centrioles absent.

(b) Late Prophase.

(c) Metaphase. The chromosomes will be arranged at the equator attached to the spindle

fibre.

(d) In Mitosis : The chromosome number in daughter cell is same as that of the mother cell

i.e., diploid mother cell gives rise to 2 diploid daughter cells.

In Meiosis : The chromosome number is halved in the daughter cells i.e., the diploid

mother cell gives rise to four haploid daughter cells.

(e)


Documents

108—113 · (15) ArunDeep’s Biology-10 Structure of Chromosomes, Cell Cycle and Cell Division PROGRESS CHECK Fill in the blanks. 1. ... (c)Chromosomes become visible as fine long