Question 1

Question 1Define the following terms:(a) Chromosome(b) Gene(c) Cell division(d) Chromatid(e) Aster

Accepted Answer

(a) Chromosome — Chromosomes are formed of very long, highly coiled and condensed chromatin fibres which are made of DNA (about 40%) and histones (about 60%). They are present in the nucleus of the cell. They carry the chemical instructions for the reproduction of the cell.(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. They are the units of heredity which are transferred from parents to offsprings and are responsible for some specific characteristics of the offspring.(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. Before replication, one chromosome is composed of one DNA molecule. In replication, the DNA molecule is copied, and the two molecules are known as chromatids. During the later stages of cell division these chromatids separate longitudinally to become individual chromosomes.(e) Aster — During mitosis in an animal cell, after the centrosome splits into two along with simultaneous duplication of the centrioles contained in it, each centriole is surrounded by radiating rays and is termed aster (meaning star).

Question 2

Question 2Give 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.

Accepted Answer

(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. This is essential because when the male and female gametes fuse during fertilization, the normal double (diploid) number of chromosomes is reacquired. The diploid number, as a rule, is expressed as “2n” and the haploid number as "n".(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 3

Question 3Distinguish between the following pairs:(a) Cytokinesis and Karyokinesis(b) DNA and RNA(c) Nucleosome and Nucleotide(d) Centrosome and Centromere(e) Haploid and Diploid

Accepted Answer

(a) Difference between Cytokinesis and KaryokinesisCytokinesisKaryokinesisIt is the division of the cytoplasm.It is the division of the nucleus.It occurs after karyokinesis.It is the first division.It results in the formation of two daughter cells.It results in the formation of two nuclei.(b) Difference between DNA and RNADNARNADNA is Deoxyribonucleic acid.RNA is Ribonucleic acid.It consists of four distinct bases: Thymine, Adenine, Cytosine and Guanine.It consists of four distinct bases: Uracil, Adenine, Cytosine and Guanine.The DNA is a double-stranded molecule.The RNA is a single-stranded molecule.It is located in the nucleus of a cell and in the mitochondria.It is found in the cytoplasm, nucleus, and in the ribosome.(c) Difference between Nucleosome and NucleotideNucleosomeNucleotideNucleosome is the complex that 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) Difference between Centrosome and CentromereCentrosomeCentromereIt is an organelle of the animal cell surrounding the centrioles, located near the nucleus.It is a non-stainable part of chromosome at which two chromatids join.It contains one or two centrioles which move towards the opposite poles and forms spindle fibres during cell division.It provides attachment of spindle fibres during cell division.(e) Difference between Haploid and DiploidHaploidDiploidOnly half the number of chromosomes (only one member from each pair) is passed on to each daughter cell.Full Set of chromosomes is passed on to each daughter cell.It is denoted by n.It is denoted by 2n.This state is found during meiotic division.This state is found during mitotic division.

Question 4

Question 5Given below are the sets of four terms. Choose the odd one and write the category of the remaining terms:(a) Adenine, Guanine, Adrenaline, Thymine(b) Pentose sugar, Histones, Phosphate group, Nitrogenous bases(c) Metaphase, Anaphase, Interphase, Telophase(d) G1 phase, M phase, G2 phase, S phase(e) Chromoplast, Chromosome, Chloroplast, Leucoplast

Accepted Answer

(a) Odd one out — AdrenalineAdenine, Guanine, Thymine — Nitrogenous bases(b) Odd one out — HistonesPentose sugar, Phosphate group, Nitrogenous bases — form nucleotide(c) Odd one out — InterphaseMetaphase, Anaphase, Telophase — Phases of Mitosis(d) Odd one out — M phaseG1 phase, G2 phase, S phase — Phases of Interphase(e) Odd one out — ChromosomeChromoplast, Chloroplast, Leucoplast — Plastids

Question 5

Question 9In the cells of a human male body, the number of autosomes is :23 pairs22 pairs1 pair46 pairs

Accepted Answer

22 pairsReason — Out of total 23 pairs of chromosomes, 22 pairs are autosomes and 1 pair is sex chromosome.

Question 6

Question 10The basis of genetic variation in the living organisms during mitosis occurs due to :Cell divisionMutationCrossing overKaryokinesis

Accepted Answer

Crossing overReason — Crossing over results in change of gene sequence which is responsible for variation.

Question 7

Question 11After a mitotic cell division, a human female cell will have :22 + X chromosomes44 + XY chromosomes44 + XX chromosomes22 + XX chromosomes

Accepted Answer

44 + XX chromosomesReason — After mitotic cell division, the resulting daughter cells will have the same number and type of chromosomes as the parent cell. A human female cell has 46 chromosomes. Out of these 46, two are sex chromosomes (XX).

Question 8

Question 12The correct sequence of phases in interphase is:G1, G2 and SS, G2 and G1G1, S and G2G2, S and G1

Accepted Answer

G1, S and G2Reason — The correct sequence is G1 → S → G2.

Question 9

Question 13The phase of karyokinesis which is almost the reverse of prophase is :InterphaseMetaphaseAnaphaseTelophase

Accepted Answer

TelophaseReason — In telophase, chromatids thin out in the form of chromatin fibres. In prophase, chromosomes become distinct.

Question 10

Question 14The lengthwise arrangement of DNA mainly consists of a phosphate group attached with :Hexose sugarPurinesPentose sugarPyrimidines

Accepted Answer

Pentose sugarReason — The lengthwise arrangement of DNA mainly consists of a phosphate group attached with five-carbon pentose (ribose) sugar.

Question 11

Question 15The number of histone proteins associated with the DNA in a nucleosome is:6841

Accepted Answer

8Reason — A nucleosome has 8 histone proteins.

Question 12

Question 16The pyrimidine bases of DNA are:Adenine and GuanineGuanine and CytosineAdenine and ThymineThymine and Cytosine

Accepted Answer

Thymine and CytosineReason — Thymine and Cytosine are pyrimidine; and Adenine and Guanine are purine.

Question 13

Question 17The female gamete/egg cell of a human cell will have:44 + XX chromosomes44 + XY chromosomes22 + X chromosomes22 + Y chromosomes

Accepted Answer

22 + X chromosomesReason — Chromosome number is halved in gametes (sex cells) so the female gamete/egg cell of a human cell will have 22 + X chromosomes.

Question 14

Question 18The figure given alongside was shown to students of class 10 in the laboratory under a compound microscope. They were told to observe the slide, identify the stage of mitotic cell division and mention the number of chromosomes which would be found in the daughter cells. Which of the following will be the correct response?Anaphase, 8 chromosomesMetaphase, 8 chromosomesAnaphase, 4 chromosomesTelophase, 4 chromosomes

Accepted Answer

Anaphase, 4 chromosomesReason — During mitosis the chromosome number remains the same, and in anaphase the sister chromatids move towards opposite ends. During this phase, in animal cell, the furrow formation starts in the cell membrane at the middle by which the cytoplasm will divide after mitosis.

Question 15

Question 6Given below is a diagram representing a stage during mitotic cell division in an animal cell. Examine it carefully and answer the questions which follow.(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:The number of daughter cells produced.The chromosome number in the daughter cells.

Accepted Answer

(a) By observing the given figure we can say that it is the late prophase stage because the nuclear membrane and nucleolus have disappeared.(b) Centrioles is the cell organelle that form the aster.(c) The parts are as follows:1 → Centromere2 → Chromatids3 → Spindle fibre(d) The stage that follows the one shown here is Metaphase. In 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) Difference between mitosis and meiosis :MitosisMeiosisIt produce two daughter cells.It produce Four daughter cells.Full set of chromosomes is passed on to each daughter cell. This is the diploid (2n) number of chromosomes.Only half the number of chromosomes is passed on to each daughter cell. This is the haploid (n) number of chromosomes.

Question 16

Question 7Given below are three diagrammatic sketches (A, B and C) of one and the same particular phase 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 cell? Give reasons.

Accepted Answer

(a) It is Metaphase.(b) The diploid number of chromosomes shown in them is 4.(c) Categorisation of cell A, B and C are as given below:Cell A - It is an animal cell as the centrosome has split into two centrioles and the centrioles have formed asters. Also, no cell wall is present.Cell B - It is an animal cell as the centrosome has split into two centrioles and the centrioles have formed asters. Also, no cell wall is present.Cell C - It is a plant cell as no centrioles are seen and cell wall is present.

Question 17

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

Accepted Answer

(a) This figure is of the animal cell because:Centrosomes on centrioles are present.Cell wall is absent(b) It is undergoing mitosis.(c) The correct sequence is B, C, D and A(d) The stage that should precede the earliest of these stages is interphase.(e) Below diagram shows interphase stage of mitosis:

Question 18

Question 4Fill 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 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.

Accepted Answer

(a) DNA replicates in the synthesis 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 chiasma during the process of crossing over.

Structure of Chromosomes, Cell Cycle and Cell Division

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Multiple Choice Type

Structured Application Skill Type

Very Short Answer Type