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Solutions for Biology, Class 10, ICSE
Assertion. Both centromere and centrosome are parts of chromosome.
Reason. The centromere is the region where spindle fibres attach, while the centrosome helps in the formation of spindle fibres.
A is False and R is True.
Explanation
Centromere is the place where spindle fibres attach and centrosome is the organelle which helps in forming spindle fibres. Centromere and centrosome are not parts of chromosome.
Assertion. The basic structural unit of DNA is nucleotide.
Reason. DNA is composed of repeating nucleosome which are made up of three components - pentose sugar, phosphate group and nitrogenous bases.
A is True and R is False.
Explanation
DNA is composed of repeating nucleosome which are made up of nucleotide and histone proteins. Nucleotide are composed of pentose sugar, phosphate group and nitrogenous bases.
Assertion. Centrosome is the point of attachment of two chromatids of a chromosome.
Reason. Centrosome initiates and regulates the process of cell division as it helps in the formation of spindle fibres.
A is False and R is True.
Explanation
Centromere is the point of attachment of two chromatids of a chromosome. Centrosomes or centrioles are structures present in cell that initiate and regulate cell division.
Assertion. Meiosis is the kind of cell-division which occurs during gamete formation in the gonads.
Reason. During meiosis, chromosome number remains the same in parent cell and daughter cells which is very significant to maintain the identity of the organism.
A is True and R is False.
Explanation
During meiosis, chromosome number is halved. During fertilisation, two haploid gametes/cells fuse to restore normal chromosome count.
(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).
(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.
(a) Difference between Cytokinesis and Karyokinesis
| Cytokinesis | Karyokinesis |
|---|---|
| It 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 RNA
| DNA | RNA |
|---|---|
| DNA 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 Nucleotide
| Nucleosome | Nucleotide |
|---|---|
| Nucleosome 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 Centromere
| Centrosome | Centromere |
|---|---|
| It 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 Diploid
| Haploid | Diploid |
|---|---|
| Only 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. |
Given 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
(a) Odd one out — Adrenaline
Adenine, Guanine, Thymine — Nitrogenous bases
(b) Odd one out — Histones
Pentose sugar, Phosphate group, Nitrogenous bases — form nucleotide
(c) Odd one out — Interphase
Metaphase, Anaphase, Telophase — Phases of Mitosis
(d) Odd one out — M phase
G1 phase, G2 phase, S phase — Phases of Interphase
(e) Odd one out — Chromosome
Chromoplast, Chloroplast, Leucoplast — Plastids
both ovary and testis
Reason — In Meiosis, the number chromosomes is halved and it occurs in the sex cells or gametes. It takes place in the reproductive organs — testis and ovary.
Prophase, metaphase, anaphase, telophase
Reason — The stages of mitosis in correct sequence are:
Prophase → metaphase → anaphase → telophase
44 + XX chromosomes
Reason — 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).
Pentose sugar
Reason — The lengthwise arrangement of DNA mainly consists of a phosphate group attached with five-carbon pentose (ribose) sugar.
22 + X chromosomes
Reason — Chromosome number is halved in gametes (sex cells) so the female gamete/egg cell of a human cell will have 22 + X chromosomes.
The 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, 4 chromosomes
Reason — 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.
Fill in the blanks:
Name these:
(a) Two main constituents of Chromatin
(b) Two kinds of Nucleic acids
(c) Three components of a Nucleotide
(d) Four Nitrogenous bases
(e) Two kinds of Nitrogenous bases
(f) Two components of Nucleosome
(g) Two kinds of Cell division
(h) Four main phases of Karyokinesis
(i) Two steps of the process Mitosis
(j) Two kinds of haploid cells of human body
(a) DNA and Histones
(b) RNA and DNA
(c) Phosphate, Sugar and Nitrogenous bases
(d) Adenine, Guanine, Thymine and Cytosine
(e) Purine and Pyrimidine
(f) DNA and Histone
(g) Mitosis and Meiosis
(h) Prophase, Metaphase, Anaphase, Telophase
(i) Karyokinesis and Cytokinesis
(j) Male gamete (22 + Y) and Female gamete (22 + X)
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 the nucleus during interphase.
Corrected statements are as follows:
(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) 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.
Given below is a schematic diagram of a portion of DNA.
(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.
(a) 2 strands are shown in the diagram.
(b) 2 on each strand.
(c) The parts are as follows:
(d) The DNA unit constituted by the parts 1, 2 and 3 collectively is called Nucleotide.
The diagram below represents a stage during cell division. Study the same and then answer 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.
(a) The parts are as follows:
(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 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. Below diagram shows metaphase:
The phenomenon shown in the diagram is termed Crossing-Over. It is the exchange of chromatid material between the two members of a homologous pair of chromosomes while the maternal and paternal chromosomes are separating.
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.
(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:
(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:
(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 :
| Mitosis | Meiosis |
|---|---|
| It 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. |
Given 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.
(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:
Shown 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.
(a) This figure is of the animal cell because:
(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:
(a) Nucleotides
(b) Nucleosome
(c) Hydrogen Bond
(d) Phosphate, Sugar and Nitrogenous base.
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 transformed into a chromatin network. | Metaphase |
| Column "A" | Column "B" |
|---|---|
| (a) Chromosomes get arranged in a horizontal plane at the equator. | Metaphase |
| (b) Daughter chromosomes move to the opposite poles of a spindle. | Anaphase |
| (c) Chromosomes become visible as fine long threads. | Prophase |
| (d) Chromosomes lose their distinctiveness and gradually become transformed into a chromatin network. | Telophase |
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 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.
(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.
