WBBSE Class 10 Life Science Solutions Chapter 2A Cell Division and Cell Cycle

Detailed explanations in West Bengal Board Class 10 Life Science Book Solutions Chapter 2A Cell Division and Cell Cycle offer valuable context and analysis.

WBBSE Class 10 Life Science Chapter 2A Question Answer – Cell Division and Cell Cycle

Short Answer Type Questions : 2 Marks

Question 1.
What is prokaryotic cell? Mention two differences between Prokaryotic and Eukaryotic cell.
Answer:
Prokaryotic cell : The most primitive type of cell are small, lacking membrane around the nucleus and the nuclear contents as protein and nuclic acid is termed as prokaryotic cell (Pro-primitive, karyon-nucleus)

Prokaryotic cell	Eukaryotic cell
i. Cell wall composed of amino sugar and muramic acid.	i. Plant cell wall composed of cellulose.
ii. Cytoplasmic organellesendoplasmic reticulum, mitochondria, golgi bodies etc. are absent.	ii. Cytoplasmic organelles endoplasmic reitculum, mitochondria, golgi bodies etc. are present.

Question 2.
What is amitosis? Give example What is cell cycle?
Answer:
Amitosis : The process of cell division in which the nucleus first constricts in the middle to divide into two nuclei and then the cell body undergoes changes without spindle formation and ultimately divides into two daughter cells are known as amitosis.
e.g. Chara, Amoeba etc. show amitosis.
Cell Cycle : The cycle through which a cell passes involving different phases of changes, when it undergoes division is called cell cycle.

Question 3.
Compare ‘cleavage’ and ‘cell plate formation’ during cell division. Mention the importance features of G₁ of cell cycle.
Dissimilarities :
Answer:

Cleavage	Cell plate formation
i. Occurs in animal cell	i. Occurs in plant cell.
ii. Formed by furrowing.	ii. Formed by aggression of golgi vesicles.

Similarity : Both helps in cytokinesis either in animal or in plant cell.
Importance of G₁ phase : Cell grows in size, RNA and protein synthesis occurs, DNA content remains unchanged.

Question 4.
Write two differences between plant and animal mitosis.
Answer:

Plant mitosis	Animal mitosis
i. Spindle is formed by microtubules of nucleoplasm.	i. Spindle is formed from astral rays of the centrosome.
ii. Absence of centromere.	ii. During division centromere is separated out and centrioles move towards opposite poles.

Question 5.
Write two major differences between plant cell cytokinesis and animal cell cytokinesis.
Answer:

Plant cytokinesis	Animal Cytokinesis
i. Cytokinesis takes place by cell plate formation.	i. Cytokinesis takes place by furrowing cleavage.
ii. In plant cell cytokinesis begins from telophase.	ii. Cytokinesis begins from anaphase.

Question 6.
What are Phragmoplasts?
Answer:
Phragmoplast is the aggregation of vesicles from golgi body which helps in plant cytokinesis.

Question 7.
Why mitosis is called equational division and meiosis is called reductional division? When meiosis cell division occurs?
Answer:
Equational division is the division in which chromosome number of parent cell and daughter cell is equal. In Mitosis, two daughter cells are produced (diploid or 2n) remain indentical to the diploid (2n) parent cell.
Reductional division is the division in chromosome. Number of daughter cell becomes half of that of mother cell. In meiosis, the daughter cells which are produced are haploid cells (n) while that of parent is a diploid cell (2n).

Question 8.
What is mitosis? What is the importance of mitosis?
Answer:
Mitosis is the process in which one eukaryotic cell divides into two cells identical to the parent cell (generally identical, since alterations in genetic material can occur, more or less organelles may be distributed between the daughter cells, etc.)
Mitosis is fundamental for asexual reproduction of eukaryotes, for the embryonic development and for tissue renewal.

Question 9.
Why in some cases is mitosis a synonym of reproduction?
Answer:
In some living beings asexual reproduction occurs by many means: binary division, schizogony, budding, grafting, etc. In asexual reproduction of eukaryotes mitosis is the mechanism by which the constituent cells of the new beings are made.
The term mitosis does not apply to prokaryotes since it involves nuclear division and eukaryotic structures.

Question 10.
What is the importance of mitosis for the embryonic development?
Answer:
Every embryo grows from a single cell that suffers mitosis and generates other cells that also divide themselves by mitosis forming tissues and complete organs. The perfect regulation and control of each of those cell divisions are fundamental for the creation of a normal individual. Without mitosis the embryonic development would be impossible.

Question 11.
What are some examples of organ and tissue where mitosis is more frequent, less frequent or practically absent?
Answer:
Generally in vertebrates mitosis is more frequent in tissues that require intense renewing due to their functions, like epithelial tissues and the bone marrow. In plants the meristem tissue has numerous cells undergoing mitosis. Mitosis takes place with low frequency in tissues of slow renovation, like the bones in adults and the connective tissues. In some adult tissues mitosis is almost absent, like the nervous tissue and the striated muscle tissue (skeletal and cardiac). The nervous tissue develops from stimulus by development of new electrical networks between cells and the striated muscle tissue grows by cellular hypertrophy.

Question 12.
How does mitosis participate in the growth of pluricellular organisms?
Answer:
All pluricellular beings grow with the increase in quantity of their cells. This increase is produced by mitosis (although some types of growth occur by cellular hypertrophy or by deposition of substances in interstitial spaces).

Question 13.
What is the uncontrolled mitotic process that occurs as disease in pluricellular beings called?
Answer:
Uncontrolled mitotic cell division is called neoplasia. Neoplasia (the formation of new strange tissues) occurs when a cell suffers mutation in its genetic material, loses the ability to control its own division and the failure is transmitted to its descendants. Cancers are malignant neoplasias. The term malignant means that neoplastic cells can disseminate to distant sites invading other organs and tissues. Neoplasias whose cells cannot disseminate to distant sites are called benign neoplasias.

Question 14.
What is cellular regeneration? How is mitosis related to this process?
Answer:
Some tissues are able to regenerate when injured. The liver, for example, regenerates when small pieces of hepatic tissue are removed, bones make new tissues in fracture regions, etc. Some animals, like planarias, are capable of regenerating their bodies when sectioned. In tissue regeneration cellular proliferation happens by mitosis.

Question 15.
What is cell cycle?
Answer:
Cell cycle, or mitotic cycle, is the time period that begins when the cell is created and finishes when it is divided by mitosis creating two daughter cells. The cell cycle is divided into interphase and the mitotic phase.

Question 16.
Is cell division happening during the entire cell cycle? What is interphase?
Answer:
Cell division properly occurs during the mitotic phase of the cell cycle. During interphase processes that are a preparation to cell division take place, like the duplication of DNA and centrioles. Interphase is the preceding phase and the mitotic is the following phase.

Question 17.
What are the three periods into which interphase is divided?
Answer:
Interphase is the preceding phase to the mitotic division. It is divided into three periods, G₁, S and G₂ (the letter G comes from “gap”, meaning interval or breach, and the letter S comes from “synthesis”, indicating the period in which DNA replicates).
In fact, “gap” is not totally appropriate for the periods immediately before and after the DNA synthesis. The idea of “growth” would be more adequate since in those periods (G₁ and G₂) the cell is growing to divide later in mitosis.

Question 18.
What are the events that mark the beginning and the end of the second interphase period? What happens in the cell in this period?
Answer:
The second interphase period is the S. It starts with the beginning of DNA replication and finishes with the end of that process. The main event in this period is the synthesis of new polynucleotide chains, each bound to each DNA chain that served as a template, i.e., the duplication of the original set of DNA molecules.

Question 19.
What are the events that mark the beginning and the end of the third interphase period? What happens in the cell in this period?
Answer:
The third interphase period is the G₂. It begins with the end of DNA replication and ends with the beginning of the first period of the mitotic phase. On G₂ the cell is growing too and the duplication of centrioles occurs (only in cells that have these structures).

Question 20.
What are centrioles? In which type of cell are they present?
Answer:
Centrioles are tiny cylindrical structures made of nine microtubule triplets. They appear in pairs in the cell. Centrioles participate in the making of cytoskeleton and of cilia and flagella. In cell division they play a role in the formation of the aster fibers. Centrioles are structures present in animal cells, in most protists and in some primitive fungi. There are no centrioles in cells of superior plants and in general it is considered that plant cells do not have centrioles (although this is not entirely correct since some plants have centriole-containing cells).
The region where the centrioles are located is called the centrosome of the cell.

Question 21.
What are the main events of the first mitotic period?
Answer:
The first mitotic period is prophase. During prophase the following events occur : migration of each centriole pair (centrioles were duplicated in interphase) to opposite cell poles; aster formation around the centriole pairs; formation of the spindle fibres between the two centriole pairs; end of chromosome condensation; disintegration of the nucleolus; breaking of the karyotheca; dispersion of condensed chromosomes in the cytoplasm; binding of chromosomes to the spindle fibres.

Question 22.
What is the mitotic apparatus?
Answer:
Mitotic apparatus is the set of aster fibres, radial structures around each centriole pair, plus the spindle fibres, fibres that extend across the cell between the two centriole pairs located in opposite cell poles. The mitotic apparatus appears in prophase and has important role in the orientation and gripping of chromosomes and other cellular elements causing them to separate and migrate to opposite cell poles.

Substances that disallow the formation of the mitotic apparatus, like colchicine, a molecule that binds to tubulin molecules and prevents the synthesis of microtubules, interrupt cell division. Colchicine is used to study chromosomes since it paralyzes mitosis when chromosomes are condensed and so are more easily viewed under the microscope.

Question 23.
What are the main events of the second mitotic period?
Answer:
The second mitotic period is metaphase. In metaphase the following events occur : condensed chromosomes bind (in their centromere region) to the spindle fibres and get concentrated in the middle of the cell; the formation of the mitotic apparatus is completed. Metaphase ends with the breaking of the binding of identical chromatids and then anaphase begins.

Question 24.
What are the main events of the third mitotic period?
Answer:
The third mitotic period is anaphase. In anaphase the following events occur: duplication and breaking of centromeres with separation of identical chromatids; traction (by the spindle fibres) of identical chromatids each to opposite cell poles; beginning of chromosome decondensation.

Question 25.
During mitotic anaphase is there separation of homologous chromosomes or separation of identical chromatids?
Answer:
In the anaphase of mitosis the identical chromatids separate and complete pairs of homologous chromosomes continue to exist in each daughter cell. The separation of the homologous chromosomes occurs in the anaphase of the cell division by meiosis.

Question 26.
What are the main events of the final mitotic period?
Answer:
The final mitotic phase is telophase. In telophase the following events occur: decondensation of chromosomes, each set located in opposite cell poles; karyotehca formation around each set of chromosomes forming two nuclei; destruction of the mitotic apparatus; reappearing of the nucleoli; beginning of cytokinesis (the division of cytoplasm to ultimately separate the new cells).

Question 27.
How does the quantity of genetic material vary within the cell during the sequential phases of the cell cycle?
Answer:
The first period of the first phase (interphase) of the cell cycle is the G₁, followed by S and G₂ and then by the mitotic phase.
In G₁ the ploidy (the quantity of DNA molecules in the cell) can be represented by the formula 2n ( n is the number of DNA molecules in a gamete cell of a given species). In S DNA duplicates and the quantity of genetic material increases from 2n to 4n. In G₂ that quantity is constant: 4n. After the mitotic phase the quantity of genetic material decreases to 2n in each daughter cell.

Question 28.
Concerning their final products (daughter cells and their ploidies) what are the differences between mitosis and meiosis?
Answer:
In mitosis one cell, for example, with 2n chromosomes, duplicates its chromosomal set and divides generating two other cells, each with 2n chromosomes too. In meiosis, one diploid cell (2n) duplicates its chromosomes too, but four cells with n chromosomes are generated.

Question 29.
Why is meiosis important for the maintenance of the normal quantity of chromosomes of a species with sexual reproduction?
Answer:
A reduction to a half of the maximum normal quantity of chromosomes is mandatory in some phase of the life cycle of a species that reproduces sexually. If that could not happen in each generation, whenever a zygote is formed by fusion of gametes there would be duplication in the quantity of chromosomes in a geometric progression.

Question 30.
What are the two divisions of meiosis? What are the main events that occur in those divisions?
Answer:
Meiosis is divided into first meiotic division, or meiosis I, and second meiotic division, or meiosis II. During meiosis I the separation of homologous chromosomes occurs, with formation of two haploid cells. In meiosis II there is separation of identical chromatids of each of the two haploid cells created in meiosis I, giving birth to four haploid cells.
Meiosis II is a process identical to mitosis.

Question 31.
In which meiotic division does the separation of the homologous occur? What are the ploidies of the generated cells after the end of that process?
Answer:
The separation of the homologous chromosomes occurs in the first division of meiosis, or meiosis I. After the end of this cell division two haploid cells are made, each having different chromosomes (with no set of homologous). Note that in the cells generated after meiosis I each chromosome is still duplicated since the homologous chromosomes and not the identical chromatids were separated.

Question 32.
In which meiotic division does the separation of identical chromatids occur? After the end of this process what are the ploidies of the new cells?
Answer:
The separation of identical chromatids occurs in the second meiotic division, or meiosis II. After this cell division (similar to mitosis and that does not alter ploidy) the cells are still haploid (they have become haploid after meiosis I).

Question 33.
In which period of meiosis does the pairing of homologous chromosomes occur?
Answer:
The pairing of homologous chromosomes is a vital step for meiosis because the rightness of the homologous separation depends on the process. This event occurs in prophase I of the cell division.

Question 34.
What is crossing over? In which period of meiosis does this event occur?
Answer:
Crossing over is the eventual.exchange of chromosomal fragments between homologous chromosomes. The phenomenon occurs in prophase I when homologous chromosomes are paired. Crossing over is of great importance for evolution and biodiversity since it provides recombination of alleles (of different genes) linked in the same chromosome during cell divison by meiosis.

Question 35.
What are the ‘chiasms’ of homologous chromosomes seen in prophase I?
Answer:
Chiasms are intersections of two tracts in the form of ‘x’.
The chiasms seen in prophase I are chromosome arms crossing over same arms of their homologous. In fact when chiasms are seen under the microscope chromatids exchange chromosomal segments with other chromatids of its homologous.

Question 36.
What are the respective functions of the separation of homologous chromosomes and of the separation of identical chromatids in meiosis?
Answer:
The separation of homologous chromosomes in meiosis I has two main functions: to reduce to half the total number of chromosomes, generating haploid daughter cells at the end of the process, and to make possible genetic recombination since the separation is aleatory, i.e., each pair of daughter cells can be different from the other pair relating chromosomal combination from paternal and maternal origins.
The separation of identical chromatids in meiosis II has the same function it has in mitosis: to separate the chromosomes already duplicated to the daughter cells.

Long Answer Type Questions : 5 Marks

Question 1.
State two significance of each of mitotic and amitotic cell division. What is gene?
Answer:
Significance of mitotic cell division :
i. Helps in growth and development of organs and body of organism.
ii. Helps in maintaining proper size.

Significance of amitetic cell division :
i. Helps in multiplication of cells in foetal membranes.
ii. Easy process.

Gene : Gene is the heriditary unit consisting of a particular sequence of basis and amino acids in DNA and specifying the production of distinct enzymatic protein in the cell.

Question 2.
Describe anaphase stage of mitosis. Write differences between Mitosis and Meiosis.
Answer:
Anaphase stage of mitosis :

1. The centromeres of the chromosomes divide and the two chromatids of each pair separate. They are called-daughter chromosomes.
2. The daughter chromosomes migrate towards poles due to shortening of spindle fibres attached to the centromeres.
3. Pulling causes the chromosomes to assume their characteristic V-shape of L-shape etc.

Mitosis	Meiosis
i. Occurs in somatic cell	i. Occurs in germ mother cell or spare mother cell.
ii. No crossing over takes place.	ii. Crossing over takes place.
iii. Two diploid cells are formed from a diploid cell.	iii. Four haploid cells are formed from a diploid cell.
iv. Cell divides only once.	iv. Cell divides twice.

Question 3.
Discuss characteristics of prophase of mitotic cell division in an animal cell.
Answer:

1. Chromosomes are condensed, thicken and become stainable.
2. Chromatids coil around each other and are held together at centromere.
3. The chromosomes are evenly distributed in the neucleoplasm.
4. Nucleoli gradually deminishes in size and disappear.
5. Centrioles duplicate and move towards opposite poles.
6. The movement of centrioles are due to they are being pushed by the growth of spindle fibres.
7.  Asters are formed from cytoplasm.

Question 4.
When does DNA synthesis occur during interphase? Discuss process of cytokinesis in plant cell and in animal cell.
Answer:
S-phase : DNA synthesis occurs.
Cytokinesis for plant cell : Cytokinesis in plant cell involves the formation of a cell wall in between the daughter nuclei. This begins as a cell plate or phragmoplast formed by aggregation of vesicles from Golgi bodies. These vesicles fuse with each other to form cell membranes and cell walls, there by the cell divides into two parts. The spindle which is also involved in the cell plate formation, then disintegrates and cell division is completed.

Cytokinesis in animal cell : A cleavage furrow appears at the outer edges of the cell and midway between the poles at the beginning. This furrow of constriction becomes progressively deeper as the spindle breaks down. Finally the ingrowing constriction joins and cleves the cell into two parts.

Question 5.
What is the name of the cytoplum divioion in the end of mitosis? What are the differences in this process ‘bétween animal and plant cells?
Answer:
Cytoplasm division occurs after telophase and it is called cytokinesis. In animal cells an invagination of the plasma membrane toward the cell centre appears in the equator of the parent cell and then the cell is strangulated in that region and divided into two daughter cells. This type of division is called centripetal cytokinesis (from outside).

In plant cells the cytokinesis is not centripetal since the division happens from the inside. Membranous sacs full of pectin concentrate in the internal central region of the cell and propagate to the periphery toward the plasma membrane. The pectin-containing sacs fuse themselves and form a central structure called phragmoplast. On the phragmoplast cellulose deposition occurs and a true cell wall is created to separate the daughter cells. Plant cells thus present centrifugal cytokinesis.
The phragmoplast has ‘failures’ or pores to permit cytoplasmic communications between the daughter cells. These openings are called plasmodesma.

Question 6.
Why is it important for chromosomes to be condensed during mitosis and decondensed during interphase?
Answer:
During mitosis the main problem to be solved is the correct separation of chromosome sets between daughter cells. If chromosomes were decondensed long, tiny fibres of DNA would be dispersed in cytoplasm after the karyotheca breaking and chromosomes could not be easily organized and pulled by the spindle fibres.

During interphase the function of chromosomes, i.e, of DNA molecules, is the synthesis of RNA and thus of proteins. For this task it is necessary for functional molecular regions to be decondensed (these regions form the euchromatin). During interphase in addition DNA replication occurs as a preparatory step for cell division. In this process it is fundamental for the exposition of DNA molecules to serve as templates to new DNA chains under production.

Question 7.
Concerning their biological function what is the difference between mitosis and meiosis?
Answer:
The main biological function of mitosis is cellular multiplication, a fundamental process for the growth and development of multicellular organisms, tissue renewing, asexual reproduction etc. The biological function of meiosis is gamete formation (in gametic meiosis) or spore formation (in sporic meiosis), i.e., the production of cells qualified for sexual reproduction with half the quantity of chromosomes compared to the original cell.

There is a special type of meiosis that happens in zygotes of some algae, protozoans and fungi. This meiosis, called zygotic meiosis, has the function of reducing half the number of chromosomes of adult individuals that will be formed from the zygote. In species with zygotic meiosis the adult individuals are haploid and they form gametes by mitosis. These gametes fuse in pairs with others and generate a diploid zygote. Then, undergoes meiosis to restitute the normal ploidy of adult individuals.

Question 8.
For the biological diversity is mitosis or meiosis the more important process?
Answer:
Meiosis is the cell division process that allows the formation of gametes to sexual reproduction, with aleatory separation of each chromosome of the individual homologous pairs. These gametes can fecundate gametes from other individuals promoting combination of homologous chromosomes from different individuals. In that manner the chromosomal recombination provided by meiosis and sexual reproduction creates individuals with dissimilar genetic patrimony from their fathers and thus promotes biological diversity.

Some fungi species and plants, for example-present sporic meiosis, i.e., a structure where half of the chromosomes of the species is generated from meiosis. This structure, by mitosis, forms gametes. Even in this case diversity comes from meiosis. Meiosis then is the cell division process that in conjunction with genetic mutations is responsible for the biological diversity. Even in species having zygotic meiosis the aleatory separation of homologous chromosomes in meiosis creates biological diversity.

Question 9.
During which meiosis division does ploidy reduction occur? Does ploidy reduction occur in mitosis?
Answer:
In the cell division by meiosis ploidy reduction occurs in meiosis II. Initially, taking as example a 2n somatic cell, ploidy increases to 4n (duplication of DNA) during interphase. During meiosis I, since homologous chromosomes are separated, ploidy falls to 2n (the original number) and then during meiosis II ploidy finally falls to n in the resulting daughter cells.

Ploidy reduction does not occur in mitosis. This fact shows that, although in meiosis ploidy is decreased from its original number, in meiosis II, a process similar to mitosis, the cause of that reduction is what happens in meiosis I, i.e., the separation of the homologous chromosomes.

Question 10.
In order for organisms to grow they must produce new cells and each cell rnus maintain the same genetic identity as the original cell. This will insure that the new cells will function properly and survive.
(a) Starting with interphase, explain how the events of the cycle insure that each new cell will be genetically identical to the original?
(b) What features of the prokaryotic genetic material eliminates the need for mitosis to insure identical daughter celis?
Answer:
(a) Replication during S phase results in two identical chromatids. They remain attached which insures proper sorting later. Chromosomes coil and condense which insures easier maneuvering of the chromosomes during mitosis. Nuclear membrane dissolves to allow greater area for movement of chromosomes. Kinetochore proteins on each chromatid allows for attachment to spindle fibers which will pull chromatids apart. Centromeres do not divide until they are in alignment to insure one chromatid moves to each new cell.

(b) The prokaryotic genome consists of only one circular chromosome. Upon replication there are only two chromosomes to sort. Each chromosome attaches to a specific site on the membrane and growth of the cell separates them. There is no need for the mitotic process to sort the chromosomes.

Question 11.
Write a short note on Cell cycle.
Answer:
Howard and Pelc (1953) first time described it. A series of changes or sequential events which occur regularly in a dividing cell is called cell cycle. The cell cycle includes the period from the beginning of one cell division to the beginning of the next cell division.
The time interval between two successive divisions is called generation time.
The cell cycle consists of two main phases i.e.
(i) Interphase or I – phase includes G₁, S, G₂ stages.
(ii) Mitosis or M – phase represents only a small part of life cycle of a cell i.e. about an hour in most cells.
i. Interphase or I-phase :
Resting phase.
Preparatory and synthetic phase of cell division. During this phase, the cell is metabolically active. An active phase for replication of DNA and synthesis of histone

proteins. This phase also involves synthesis of energy-rich compounds to supply energy. The interphase is further divided into three sub-phases : (a) G₁ phase (b) S phase (c) G₂ phase

G₁ phase : First phase. Also called the post-mitotic gap phase. The cell grows in size due to synthesis of RNA, nucleotides, amino acids and proteins. In some cases, cell may not divide and it enters a quiescent stage called GG₀ phase. It is also called as restriction point.

S phase : It is synthetic phase. It occurs between G₁ phase and G₂ phase. Replication of DNA takes place during this stage. DNA content doubles and a duplicate set of chromosomes is formed.

G₂ phase: Second phase. Also called the pre-mitotic gap phase. Synthesis of spindle proteins and RNA. The cell prepares to enter mitotic phase. Duplication of cell organelles also takes place.

ii. Mitosis or M-phase : Shortest phase in the cell cycle. A cell divides to form two daughter cells, identical to each other and also to the mother cell. The division of nucleus and cytoplasm occurs only once.

During mitosis, the number of chromosomes remains the same. Mitosis can take place in both haploid and diploid cells.

Also Called :
Somatic cell division : Cell division results in the formation of somatic body cells.

Equational division: Mitosis maintains chromosome number in daughter cells equal to that of the mother cell.

Question 12.
Describe about mitosis with proper diagram.
Answer:
The term ‘Mitosis’ was coined by Walther Flemming, a German biologist who for the first time observed dividing cell in 1878. Mitosis takes place in two stages: Karyokinesis and Cytokinesis.
(i) Karyokinesis (Nuclear division) : Nucleus undergoes a series of changes to form two daughter nuclei. Various stages of Karyokinesis are prophase, metaphase, anaphase and telophase.

a. Prophase (pro = first; phase = stage) :
Longest phase of mitosis. During early prophase, chromosomes become short and thick due to condensation and coiling. It appears as single-stranded (monad chromosome), but by the end of prophase, it appears double-stranded (dyad chromosome). It consists of two identical chromatids joined by a centromere. In late prophase, the nuclear membrane and nucleolus begin to disappear. The centrioles (in animal cells) start moving in opposite direction, till they occupy polar position.

b. Metaphase (meta = middle; phase = stage) :
Nuclear membrane and nucleolus completely disappear. The short and thick chromosomes get organized along the equatorial plane of the cell. Formation of spindle fibres takes place. Spindle fibres are fine thread-like structures formed by the proteins called tubulin. Tubulin is organized into protein units called microtubules. Spindle fibres are made up of microtubules. The spindle fibres are of two types.
Continuous fibres or non-chromosomal fibres : Fibres extend from pole to pole. Discontinuous or chromosomal fibres: Fibres extend from pole to centromere. Metaphase is the best stage to count the number of chromosomes during mitosis.
c. Anaphase (ana = up; phase = stage) :
It is the shortest phase of karyokinesis in which the centromere divides into two, resulting in the separation of chromatids.

Each separated chromatid is now called the daughter chromosome. The sister chromatids repel each other.

The chromosomal spindle fibres undergo contraction and pull the daughter chromosomes to the respective poles to form two groups of chromosomes.
d. Telophase ( telo = end; phase = stage ) :
The separated daughter chromosomes undergo uncoiling to form long thin chromosomes which become indistinct to form chromatin network.

The nuclear membrane begins to reappear around each group of chromosomes to form a daughter nucleus.

The spindle fibres disappear while nucleolus reappears in each newly formed nucleus.
Cytokinesis :
Cytokinesis: Division of cytoplasm of the mother cell. Cytokinesis starts at the end of telophase.

In animal cells : Cytokinesis occurs by furrowing of plasma membrane (cleavage). In animal cell, cytokinesis takes place by cleavage constriction of cell cytoplasm. It begins peripherally and centripetally.

In plant cells : Cytokinesis takes place by formation of cell plate. Cell plate is first laid down in centre and then proceeds towards periphery. Vesicles provided by Golgi apparatus join to form phragmoplasts, which further join to form cell plate.
Cytokinesis results in formation of two daughter cells.
Significance of Mitosis :
Growth and development of multicellular organisms take place by forming new somatic cells.

• It maintains surfaces volume ratio of the cell.
• It maintains chromosome number of parent cell in the daughter cells.
• It plays a significant role in the reproduction of unicellular organisms.
• It plays an important role in healing and repairs by producing new cells.
• Mitosis distributes and carries hereditary materials or genes to the next generation.

Question 13.
Write a short note on Amitosis?
Answer:
Discovered by Remark. No synthesis of spindle fibres. No condensation of chromatin fibres. No disappearing of nuclear membrane.
Occurrence : In prokaryotes, in yeast cells, in eukaryotes Amoeba, meganucleus of Paramecium, endosperm cells, foetal membrane cells etc.
Mechanism : Two steps; Karyokinesis (karyon = nucleus; kinesis = movement): Nucleus divides into two.
Cytokinesis (kytos = cell; kinesis = movement): Cytoplasm divides and two cells are formed. Unequal distribution of chromatin in the daughter cells, leads to structural and functional irregularities.

Multiple Choice Questions : 1 Mark

Question 1.
The phase of mitosis cell division in which two sister chromatids are separated is _______.
(a) Prophase
(b) Metaphase
(c) Anaphase
(d) Telophase
Answer:
(c) Anaphase

Question 2.
In a DNA molecule complementary base pair of guanine is _______.
(a) Adenine
(b) Cytosine
(c) Thymine
(d) Uracil
Answer:
(b) Cytosine

Question 3.
Number of chromosome present in germ cell of man is _______.
(a) 46
(b) 47
(c) 23
(d) 22
Answer:
(c) 23

Question 4.
In RNA molecule the complementary base of adenine is _______.
(a) Guanine
(b) Thymine
(c) Uracil
(d) Cytosine
Answer:
(c) Uracil

Question 5.
The phase of mitosis cell division in which two sister chromatids are separated is
(a) Prophase
(b) Metaphase
(c) Anaphase
(d) Telophase
Answer:
(c) Anaphase

Question 6.
Who discovered Meiosis?
(a) Flemming
(b) Weldeyar
(c) Farmar
(d) Pavlov
Answer:
(c) Farmar

Question 7.
The number of chromosomes of pollen mother cell is 10 . The number of chromosomes of the flower of some plant will be
(a) 10
(b) 20
(c) 5
(d) 30
Answer:
(b) 20

Question 8.
Who named the chromatins as chromosomes?
(a) Flemming
(b) Waldeyar
(c) Farmar
(d) Pavlov
Answer:
(b) Waldeyar

Question 9.
In which of the stages of mitotic cell division does the nuclear membrane reappear?
(a) Prophase
(b) Metaphase
(c) Telophase
(d) Anaphase
Answer:
(d) Anaphase

Question 10.
In the specific part of DNA chain, if there be adenine and guanine in one chain then which N₂ bases will be present in another chain as a complementary base respectively?
(a) Thymine and cytosine
(b) Thymine and adenine
(c) Guanine and cytosine
(d) Adenine and thymine
Answer:
(a) Thymine and cytosine

Question 11.
Chromosomes move towards the polar region of spindle during
(a) Prophase
(b) Metaphase
(c) Telophase
(d) Anaphase
Answer:
(b) Metaphase

Question 12.
Chromosome number of human gamet is _______.
(a) 32 pairs
(b) 23 pairs
(c) 32
(d) 23
Answer:
(d) 23

Question 13.
Chromosomes can be best at the stage of
(a) Late anaphase
(b) Telophase
(c) Metaphase
(d) Late prophase
Answer:
(c) Metaphase

Question 14.
In mitosis chromosome duplication occurs during
(a) Interphase
(b) Prophase
(c) Late prophase
(d) Late telophase
Answer:
(a) Interphase

Question 15.
In mitosis the number of chromosome sets in daughter cells
(a) half the number in the parent cell
(b) twice the number
(c) one fourth the number
(d) same as in parent cell
Answer:
(d) same as in parent cell

Question 16.
A complete set of chromosome inherited as a unit from one parent is known as
(a) genotype
(b) karyotype
(c) genepool
(d) genome
Answer:
(d) genome

Question 17
Separation of sister chromatids takes place in
(a) anaphase of mitosis
(b) anaphase I of meiosis
(c) anaphase II of meiosis
(d) anaphase of mitosis and anaphase II of meiosis
Answer:
(d) anaphase of mitosis and anaphase II of meiosis

Question 18.
Homologous chromosomes are separated during
(a) anaphase of mitosis
(b) metaphase of meiosis
(c) anaphase I of meiosis
(d) anaphase I of meiosis and anaphase of mitosis
Answer:
(d) anaphase I of meiosis and anaphase of mitosis

Question 19.
Longest phase in cell cycle
(a) G₁
(b) S
(c) G₂
(d) M
Answer:
(a) G₁

Question 20.
Which is the longest phase in Meiosis I?
(a) Prophase I
(b) Metaphase I
(c) Anaphase I
(d) Telophase I
Answer:
(a) Prophase I

Question 21
Synapsis is characteristic of?
(a) Leptotene
(b) Zygotene
(c) Pachytene
(d) Diplotene
Answer:
(b) Zygotene

Question 22.
Which is the longest stage of Prophase I of Meiosis 1 ?
(a) Leptotene
(b) Zygotene
(c) Pachytene
(d) Diplotene
Answer:
(c) Pachytene

Question 23.
Synaptonemal complex completed düring
(a) Leptotene
(b) Zygotene
(c) Pachytene
(d) Diplotene
Answer:
(c) Pachytene

Question 24.
Terminalisation of chiasma occurs at
(a) Diakinensis
(b) Pachytene
(c) Zygotene
(d) Diplotene
Answer:
(a) Diakinensis

Question 25.
Chiasmata in cell division is seen in
(a) Leptotene
(b) Zygotene
(c) Pachytene
(d) Diplotene
Answer:
(d) Diplotene

Question 26.
Synapsis is the pairing of
(a) Homologous chromosomes
(b) Non homologous chromosomes
(c) Analogous chromosomes
(d) Paralogous chromosomes
Answer:
(a) Homologous chromosomes

Question 27
The chromosomes appear as long thin threads in
(a) Leptotene
(b) Zygotene
(c) Pachytene
(d) Diplotene
Answer:
(a) Leptotene

Question 28.
A cell in G₁ of interphase has 12 chromosomes how many chromatids will be found during metaphase two of meiosis?
(a) 6
(b) 12
(c) 18
(d) 24
Answer:
(b) 12

Question 29.
How many gametes would be formed from a genotype AaBBccDdEe?
(a) 8
(b) 16
(c) 32
(d) 64
Answer:
(a) 8

Question 30
Amitosis is _______.
(a) cleavage of nucleus without recognizable chromosomes
(b) a division in which chromosomes are unequally distributed
(c) a division in which chromosome bridge are formed
(d) a division in which spindles are formed
Answer:
(a) cleavage of nucleus without recognizable chromosomes

Question 31.
Homologous chromosome includes
(a) one smaller and one bigger chromosome
(b) one chromosome from each parent
(c) one complete and one incomplete chromosome
(d) none of these
Answer:
(b) one chromosome from each parent

Question 32.
How many mitotic division must occur in a cell of the root tip to form \mathbf{1 2 8 cells?
(a) 7
(b) 8
(c) 64
(d) 128
Answer:
(a) 7

Question 33.
The minimum number of meiotic division to obtain 100 pollen grains of wheat
(a) 25
(b) 50
(c) 75
(d) 100
Answer:
(a) 25

Question 34.
The minimum number of chiasmata in a bivalent is
(a) 1
(b) 2
(c) 3
(d) 4
Answer:
(a) 1

Question 35.
Chromosome exhibits minimum coiling during
(a) Prophase
(b) Metaphase
(c) Anaphase
(d) Telophase
Answer:
(a) Prophase

Question 36.
Interkinesis is a period between
(a) Prophase I and metaphase I
(b) Metaphase I and anaphase I
(c) Anaphase I and telophase I
(d) Meiosis I and meiosis II
Answer:
(d) Meiosis I and meiosis II

Question 37.
Down syndrome is caused due to nondisjunction of chromosomes at
(a) Anaphase of mitosis
(b) Metaphase I of meiosis
(c) Anaphase I of meiosis
(d) Telophase I of meiosis
Answer:
(c) Anaphase I of meiosis

Question 38.
Cell cycle progression from one phase to another is primarily controlled by
(a) phosphorylation of CDKs
(b) proteolysis of cyclin
(d) dephosphorylation of cyclin
(e) proteolysis of CDKs
Answer:
(a) phosphorylation of CDKs

Question 39.
CDK associated with S phase
(a) CDK 2
(b) CDK 1
(c) CDK 3
(d) CDK 4
Answer:
(a) CDK 2

Question 40.
DNA sequence is responsible for chromatid separation
(a) centromere
(b) telomere
(c) kinetochore
(d) satellite
Answer:
(a) centromere

Question 41.
During cell cycle sister chromatids are pulled apart during
(a) Metaphase
(b) Anaphase
(c) Prophase
(d) Interphase
Answer:
(b) Anaphase

Question 42.
Among the following the most variable stage of cell cycle is
(a) G₁
(b) S
(c) G₂
(d) M
Answer:
(a) G₁

Question 43.
The Mendelian law of independent assortment is due to the arrangement of chromosome during
(a) anaphase I
(b) anaphase II
(c) S phase
(d) cytokinesis
Answer:
(a) anaphase I

Question 44.
If cell has 46 chromosomes at the beginning of mitosis, then at anaphase there would be a total of
(a) 23 chromatids
(b) 46 chromatids
(c) 46 chromosomes
(d) 92 chromosomes
Answer:
(d) 92 chromosomes

Question 45.
If a cell has 46 chromosomes at the beginning of meiosis, then at anaphase I there would be a total of
(a) 23 chromatids
(b) 46 chromatids
(c) 46 chromosomes
(d) 92 chromosomes
Answer:
(b) 46 chromatids

Question 46.
Approximately how many cells are present in the body of an adult person ?
(a) 1014
(b) 1015
(c) 1018
(d) 1021
Answer:
(d) 1021

Question 47.
The period between two successive cell divisions is called
(a) Duplication
(b) Growth phase
(c) Cell cycle
(d) Interphase
Answer:
(d) Interphase

Question 48.
Which is fundamental property of all living organisms ?
(a) Respiration
(b) Germination
(c) Growth
(d) Photosynthesis
Answer:
(a) Respiration

Question 49.
Which factors are required for growth ?
(a) An increase in group of cells, a duplication of genetic material
(b) An increase in group of cells, production of daughter cells by mitosis
(c) A dupliction of genetic material and a division assuring that daughter cells receive an equal complement of genetic material.
(d) An increase in cell mass, a duplication of genetic material, a division assuring that each daughter cell receives an equal complement of the genetic material
Answer:
(d) An increase in cell mass, a duplication of genetic material, a division assuring that each daughter cell receives an equal complement of the genetic material

Question 50.
With how many cell, reproduction starts ?
(a) Two cells
(b) Single cell
(c) Many cells
(d) Somatic cell
Answer:
(b) Single cell

Question 51.
Which of the following is present in maximum number in an adult person ?
(a) Somatic cell
(b) Gamete
(c) Reproductive cell
(d) Zygote
Answer:
(a) Somatic cell

Question 52.
At the end of which stage does cell enter mitosis ?
(a) G₁ – phase
(b) S – phase
(c) M – phase
(d) G₂– phase
Answer:
(d) G₂– phase

Question 53.
What is synthesized during G₂ – phase ?
(a) Protein
(b) Micro tubules
(c) RNA
(d) (a)and(b)
Answer:
(b) Micro tubules

Question 54.
The sequence in the cell cycle is _______.
(a) S, G₁ G₂ M
(b) G₁, S G, M
(c) S, MG₁, G₂, M
(d) G₂, S, M, G₁
Answer:
(b) G₁, S G, M

Question 55.
Synthesis of RNA and protein takes place in which phase of the cell cycle?
(a) S-phase
(b) M-phase
(c) G₁-phase ,
(d) Metaphase
Answer:
(a) S-phase

Question 56.
During mitosis, ER and nucleolus begin to disappear at
(a) Late prophase
(b) Early prophase
(c) Late metaphase
(d) Early metaphase
Answer:
(b) Early prophase

Question 57.
Mitosis is similar to
(a) Meiosis I
(b) Meiosis II
(c) Both a and b
(d) None of these
Answer:
(b) Meiosis II

Question 58.
Which of the following represents the best stage to view the shape, size and number of chromosomes?
(a) Interphase
(b) Prophase
(c) Metaphase
(d) Telophase
Answer:
(c) Metaphase

Question 59.
During metaphase mitosis chromosomes
(a) undergo coiling
(b) line up at the equator
(c) break and disintegrate
(d) none of these
Answer:
(b) line up at the equator

Question 60.
Number of chromatids at metaphase is
(a) Two each in mitosis and meiosis
(b) Two in mitosis and one in meiosis
(c) Two in mitosis and four in meiosis
(d) One in mitosis and two in meiosis
Answer:
(a) Two each in mitosis and meiosis

Question 61.
During cell division in apical meristem, the nuclear membrane appears in
(a) Metaphase
(b) Telophase
(c) Anaphase
(d) Cytokinesis
Answer:
(b) Telophase

Question 62.
Mitotic anaphase differs from metaphase in possessing
(a) Same number of chromosomes and same number of chromatids
(b) Half number of chromosomes and half number of chromatids
(c) Half number of chromosomes and same number of chromatids
(d) Same number of chromosomes and half number of chromatids
Answer:
(d) Same number of chromosomes and half number of chromatids

Question 63.
How many mitotic divisions are needed for a single cell to make 128 cells?
(a) 7
(b) 14
(c) 28
(d) 32
Answer:
(a) 7

Question 64.
Which aspect of mitosis is affected by colchicine in inducing polyploidy?
(a) DNA replication.
(b) Spindle formation
(c) Formation of cell plate
(d) Chromosome doubling
Answer:
(b) Spindle formation

Question 65.
If you are provided with root tips of onion in your class and are asked to count the chromosomes, which of the following stages can you most conveniently look into?
(a) Prophase
(b) Metaphase
(c) Anaphase
(d) Telophase
Answer:
(b) Metaphase

Question 66.
Meiosis takes place
(a) Only in haploid individuals
(b) Only in diploid individuals
(c) Both in haploid and diploid individuals
(d) None of these
Answer:
(b) Only in diploid individuals

Question 67.
In one of the following stages of cell division, the DNA content is doubled. It is
(a) G₁ phase
(b) G₂ phase
(c) Metaphase
(d) S phase
Answer:
(d) S phase

Question 68.
Amitosis is the usual process of cell division in
(a) Meristematic cells
(b) Prokaryotic cells
(c) Eukaryotic cells
d) Spore mother cells
Answer:
(b) Prokaryotic cells

Question 69.
During synapsis the number of thread (Chromonemata) in each chromosome is
(a) 2
(b) 4
(c) 8
(d) Many
Answer:
(a) 2

Question 70.
Homologous chromosomes are
(a) Morphologically and genetically similar
(b) Morphologically similar
(c) Those which pair during synapsis
(d) None of these
Answer:
(c) Those which pair during synapsis

Question 71.
Cell division of mitosis is a normal process in a living cell but sudden and abnormal mitosis in an organ will sometime result in
(a) Cancer
(b) New organ
(c) Zygote
(d) Gastrula
Answer:
(a) Cancer

Question 72.
Synapsis is characteristic of
(a) Leptotene
(b) Diplotene
(c) Zygotene
(d) Pachytene
Answer:
(c) Zygotene

Question 73.
The mechanism ensuring genetic continuity in mitosis is
(a) Having of chromosome number between the two new cells
(b) Formation of cells with 8 chromosomes
(c) Formation of two daughter cells
(d) Formation of two cells with identical kind of DNA
Answer:
(d) Formation of two cells with identical kind of DNA

Question 74.
During meiosis, crossing over occurs at
(a) Diplotene
(b) leptotene
(c) Pachytene
(d) Diakinesis
Answer:
(a) Diplotene

Question 75.
How many generations of mitotic division must occur in a cell of root tip to form 256 cells?
(a) 8
(b) 32
(c) 64
(d) 128
Answer:
(a) 8

Question 76.
Which of the following is not true concerning mitosis?
(a) Animal cells have centrioles while plant cells do not.
(b) Both plant and animal cells undergo cytokinesis.
(c) Mitosis allows growth and increases in size in both plants and animals.
(d) Animal cells form a cell plate during cytokinesis while plant cells do not
Answer:
(d) Animal cells form a cell plate during cytokinesis while plant cells do not

Question 77.
The term that refers to division of the cytoplasm is
(a) cytokinesis
(b) anaphase
(c) apoptosis
(d) karyokinesis
Answer:
(a) cytokinesis

Question 78.
Cancer cells require lot of nutrients, which are supplied by blood vessels. The growth of new blood vessels to cancerous tissue is called
(a) angiogenesis
(b) metastasis
(c) carcinogenesis
(d) apoptosis
Answer:
(a) angiogenesis

Question 79.
Which is not true about bacterial chromosomes?
(a) There is generally only one chromosome in each bacterial cell.
(b) A bacterial chromosome is present in a single copy per cell.
(c) A bacterial chromosome is attached to the plasma membrane.
(d) A bacterial chromosome contains both DNA and associated histones.
Answer:
(d) A bacterial chromosome contains both DNA and associated histones.

Question 80.
The structure that contains the genetic information in a bacterial cell is called the
(a) nucleus
(b) nuçleoid
(c) nucleolus
(d) nucleosome
Answer:
(b) nuçleoid

Question 81.
The term “nucleoid” is built from the Latin and Greek root word meaning
(a) “center” and “outside.”
(b) “kernel-like.”
(c) “true-center.”
(d) “master control.”
Answer:
(b) “kernel-like.”

Question 82.
Virtually all specialized cells of multicellular organisms
(a) develop through mutation from less specialized cells of the organism.
(b) contain more genetic material than less specialized cells of the same organism.
(c) contain less genetic material than less specialized cells of the same organism.
(d) have the same amount of DNA and the same number of chromosomes as all other cells of the organism.
Answer:
(d) have the same amount of DNA and the same number of chromosomes as all other cells of the organism.

Question 83.
The term used for DNA in a nucleus before it becomes condensed in preparation for mitosis is
(a) eukaryote
(b) chromosome
(c) chromatin.
(d) cytokinesis
Answer:
(c) chromatin.

Question 84.
Generally, animals build an organism using the diploid number of chromosomes. However, insects in the order of ants, wasps and bees can use a haploid-diploid system where adults of one sex are formed with a haploid number of chromosomes. This would mean that
(a) a single set of chromosomes is sufficient to code for a functional individual.
(b) a female could determine the sex of the offspring by fertilizing or not fertilizing an egg.
(c) the males and females are not equally “related” to their mothers considering the proportion of genes held in common.
(d) not all animals must be diploid in order to be viable organisms.
Answer:
(d) not all animals must be diploid in order to be viable organisms.

Question 85.
Which is not true about the chromosomes of a multicellular organism?
(a) They are made up of DNA and protein
(b) Each chromosome is replicated into two chromatids during the S phase of interphase
(c) Each chromosome separates into two daughter chromosomes by binary fission
(d) All cells contain chromosomes that carry the same genetic information.
Answer:
(c) Each chromosome separates into two daughter chromosomes by binary fission

Question 86.
In prokaryotes the chromosome is held in a region called the
(a) nucleoid
(b) centriole
(c) centrosome
(d) kinetochore
Answer:
(a) nucleoid

Question 87.
Generally, complex organisms do require more genes to control their synthesis and organization than do primitive organisms. However, the numbers of chromosomes vary from ants with 2 , molds with 8-14, humans with 46, potatoes with 100 and the crayfish with 200 . Given this, then
(a) there must be no relationship between amount of genetic information and complexity of the organism
(b) the number of genes per chromosome may vary among organisms, preventing a simple relationship between chromosome number and complexity.
(c) mitosis must differ from organism to organism.
(d) simpler organisms have more DNA than more complex organisms.
Answer:
(b) the number of genes per chromosome may vary among organisms, preventing a simple relationship between chromosome number and complexity.

Question 88.
Which statement is not true about eukaryotic chromosomes?
(a) There is only one chromosome of each type in each body cell.
(b) Chromosomes contain both DNA and associated histones.
(c) Chromosomes condense from chromatin at the start of mitosis.
(d) Chromosomes disperse back into chromatin at the end of mitosis.
Answer:
(a) There is only one chromosome of each type in each body cell.

Question 89.
The diploid (2n) number of chromosomes for humans is
(a) 23
(b) 24
(c) 44
(d) 46
Answer:
(d) 46

Question 90.
The haploid (n) number of chromosomes for humans is
(a) 23
(b) 24
(c) 44
(d) 46
Answer:
(a) 23

Question 91.
Which statement is NOT true about mitosis?
(a) Mitosis is a process that duplicates and divides the nuclear contents only.
(b) Mitosis produces two daughter cells that contain the same number of chromosomes as the parent cell.
(c) Mitosis produces two daughter cells that contain the same kinds of chromosomes as the parent cell.
(d) Mitosis uses a 2n parent cell to form daughter cells containing n chromosomes
Answer:
(d) Mitosis uses a 2n parent cell to form daughter cells containing n chromosomes

Question 92.
Which represents the correct sequence of stages in the cell cycle?
(a) G₁, G₂, S, M
(b) G₁, G₂, M, S
(c) G₁, M, G₂, S
(d) G₁, S, G₂, M
Answer:
(d) G₁, S, G₂, M

Question 93.
Below the skin are “stem cells” that divide with some cells continuing the stem cell line and others being pushed toward the surface to flatten and sloughed off. In the bone marrow are other stem cells producing cells such as the erythrocytes that lose their nucleus and function for a few months in the bloodstream before they too die. Such “dead end” cells that reproduce no further
(a) leave the cell cycle in a GG₀ phase, which immediately follows telophase.
(b) leave the cell cycle in G₃ phase, which immediately follows G₂
(c) halt in the midst of the S phase
(d) continually cycle but simply fail to go through cytokinesis
Answer:
(a) leave the cell cycle in a G₀ phase, which immediately follows telophase.

Question 94.
At the completion of mitosis which of the following is not true?
(a) The cell has not yet undergone the G₂ phase
(b) Each replicated chromosome has been separated into single chromatids.
(c) The daughter cell nuclei have acquired the same number and kinds of chromosomes as the parent cell nucleus.
(d) The cell may not have yet undergone cytokinesis
Answer:
(a) The cell has not yet undergone the G₂ phase

Question 95.
The critical checkpoints that control the cell cycle are at the
(a) G₁ to S stage and G₂ to M stage
(b) S to G₂ stage and G₂ to M stage
(c) M to G₁ stage and G₂ to M stage.
(d) M to G₁ stage and S to G₂ stage.
Answer:
(a) G₁ to S stage and G₂ to M stage

Question 96.
During which stage of the cell cycle is cell growth and replication of organelles most significant?
(a) M phase
(b) G₁ phase
(c) G₂ phase
(d) S phase
Answer:
(d) S phase

Question 97.
Which stage is most associated with a cell that is unable to divide again, such as a muscle or nerve cell?
(a) M phase
(b) G₁ phase
(c) G₂ phase
(d) G₀ phase
Answer:
(d) G₀ phase

Question 98.
Which sequence of stages in mitosis is correct?
(a) prophase, anaphase, prometaphase, metaphase, telophase
(b) prophase, telophase, anaphase, prometaphase, metaphase
(c) prophase, prometaphase, metaphase, anaphase, telophase
(d) telophase, anaphase, prophase, prometaphase, metaphase
Answer:
(c) prophase, prometaphase, metaphase, anaphase, telophase

Question 99.
Which occurs in metaphase?
(a) Centrioles move to opposite poles.
(b) Chromosomes line up along the equator of the dividing cell
(c) Chromosomes move to opposite poles.
(d) The nuclear envelope disappears.
Answer:
(b) Chromosomes line up along the equator of the dividing cell

Question 100.
Which occurs in anaphase?
(a) Centrioles move to opposite poles.
(b) Chromosomes line up along the equator of the dividing cell
(c) Chromosomes move to opposite poles
(d) The nuclear envelope disappears.
Answer:
(c) Chromosomes move to opposite poles

Question 101.
Plant cells differ from animal cells in mitosis in all except which of these ways?
(a) Plants lack centrioles, but animals have them
(b) Plants lack microtubules and spindles, but animals have them
(c) Plants lack cell furrows, but animals have them
(d) Plants form a cell plate, but animals do not
Answer:
(b) Plants lack microtubules and spindles, but animals have them

Question 102.
Which does not occur in telophase?
(a) Cytokinesis usually gets under way
(b) The nuclear envelope is being constructed
(c) The centromeres split apart
(d) Chromosomes decondense into chromatin
Answer:
(c) The centromeres split apart

Question 103.
Cytokinesis in plant cells differs from animal cells in the following way
(a) The plant endoplasmic reticulum forms a cell plate.
(b) Microtubules are constructed into a cell plate pattern
(c) The Golgi apparatus produces vesicles that migrate along microtubules and fuse to become a cell plate
(d) The inner plasma membrane divides by cytokinesis as in animal cells and then secretes a cellulose cell wall.
Answer:
(c) The Golgi apparatus produces vesicles that migrate along microtubules and fuse to become a cell plate

Question 104.
Binary fission by bactería differs from mitosis because
(a) the chromosome copies attach to the plasma membrane and are pulled apart by cell growth
(b) the chromosome is a simple DNA ‘strand without complex proteins and no spindle forms
(c) there is no nuclear membrane to break down and rebuild
(d) All of the choices are correct.
Answer:
(d) All of the choices are correct.

Question 105.
In multicellular organisms, mitosis is
(a) the means of tissue growth and repair
(b) a way of generating new kinds of mutant or recombinant organisms
(c) the means of sexual reproduction
(d) not useful in stem cell lines that constantly replace skin etc.
Answer:
(a) the means of tissue growth and repair

Question 106.
Which of the following is not true about cancer cells?
(a) They never fully differentiate.
(b) They exhibit contact inhibition.
(c) They exhibit uncontrolled growth
(d) They exhibit disorganized growth.
Answer:
(b) They exhibit contact inhibition.

Question 107.
Which is not correctly associated with cancer?
(a) Angiogenesis forms new blood vessels and brings nutrients and oxygen to the tumor
(b) The disorganized mass of cells is encapsulated and does not invade adjacent tissue
(c) Metastasis establishes new tumors distant from the site of the primary tumor
(d) Cells have receptors to adhere to basement membranes, then secrete proteinase enzymes to invade underlying tissues
Answer:
(b) The disorganized mass of cells is encapsulated and does not invade adjacent tissue

Question 108.
Development of a tumor from a benign form to a malignant form is dependent upon
(a) growth of blood vessels into the tumor
(b) growth of the tumor
(c) Movement of tumor cells from the original location to another part of the body
(d) Lack of function of the cells in the tumor
Answer:
(c) Movement of tumor cells from the original location to another part of the body

Question 109.
Although cancer may originate in many regions of the body, many patients die from cancerous growth in the lungs, lymph glands, or liver. This is most readily explained as
(a) spreading of cancer by angiogenesis
(b) metastasis occurring more commonly in organs that have a filter effect
(c) proteinase enzymes making cancer particularly damaging to these tissues
(d) growth anywhere but in these organs is called benign
Answer:
(b) metastasis occurring more commonly in organs that have a filter effect

Question 110.
Apoptosis refers to cell death and
(a) is always biologically detrimental to an organism
(b) is merely the accumulation of genetic errors
(c) can be programmed and is essential to normal development
(d) is a failure in the translation or transcription mechanism
Answer:
(c) can be programmed and is essential to normal development

Question 111.
Stages of the cell cycle include
(a) G₁ stage
(b) mitotic stage
(c) cytokinesis
(d) All of the choices are correct.
Answer:
(d) All of the choices are correct.

Question 112.
Most of the cell cycle is spent in
(a) prophase
(b) cytokinesis
(c) interphase
(d) anaphase
Answer:
(c) interphase

Question 113.
Apoptosis
(a) is programmed cell death
(b) is a process that acts to decrease the number of somatic cells
(c) works to oppose the effects of mitosis
(d) All of the choices are correct.
Answer:
(d) All of the choices are correct.

Question 114.
Eukaryotic chromosomes
(a) consist of both DNA and protein.
(b) may occur as chromatin
(c) contain histones responsible for packaging DNA to fit into a small space
(d) All of the choices are correct.
Answer:
(d) All of the choices are correct.

Question 115.
The overall process of mitosis functions to ensure
(a) growth and tissue repair
(b) that each new cell receives a complete set of genetic information
(c) asexual reproduction in some species
(d) All of the choices are correct
Answer:
(d) All of the choices are correct

Question 116.
The event that signals the start of anaphase is
(a) division of the centromeres to separate sister chromatids
(b) migration of the centrioles to opposite poles of the nuclear space
(c) a cleavage furrow starts to form
(d) asters disappear

Answer:
(a) division of the centromeres to separate sister chromatids

Question 117.
Chrcimosomes typically appear like the above diagram in which stage of the : cell cycle?
(a) G₁
(b) G₂
(c) S
(d) Late prophase and metaphase
Answer:
(d) Late prophase and metaphase

Question 118.
What is the term for the structure labelled D ?
(a) centromere
(b) chromosome
(c) kinetochore
(d) chromatid
Answer:
(d) chromatid

Question 119.
Which structure is responsible for attaching to a spindle fibre?
(a) structure “A”
(b) structure ” B ”
(c) structure “C”
(d) structure “D”
Answer:
(c) structure “C”

Question 120.
Which of the statements is not true of the above chromosome?
(a) The chromosome is only highly coiled like this during mitosis
(b) Each half of the chromosome is genetically different from the other
(c) Each half will split from the other during anaphase.
(d) Each half of the above chromosome will again be called a chromosome after they split from each other
Answer:
(b) Each half of the chromosome is genetically different from the other

Very Short Answer Type Questions : 1 Mark

Question 1.
What is chromosome?
Answer:
Chromosome : Intranuclear gene bearing fixed numbered, rod shaped structures which become clearly visible during metaphase and anaphase to cell division.

Question 2.
Where does meiosis occur?
Answer:
Germ mother cell.

Question 3.
Mention different stages of cell cycle.
Answer:
(i) G₁ phase (ii) S Phase (iii) G₂ phase
(iv) Mitotic phase [Prophase, Metaphase, Anaphase, Telophase, Cytokinesis, GG₀]

Question 4.
Name the cytoplasmic organelle that helps in the formation of cell plate.
Answer:
Golgi vesicles.

Question 5.
Where is centromere situated?
Answer:
Within primary constriction.

Question 6.
Name the N₂ base which is only present in RNA but not in tpNA.
Answer:
Uracil

Question 7.
In which phase of mitotic cell division nucleus reappears?
Answer:
Telophase.

Question 8.
In which type of cell division the nuclear membrane does not disappè ar? State the importance of S-phase and G₂– phase.
Answer:
Amitosis.
Importance of S-phase : New DNA is synthesized
Importance of G₂ phase : Synthesis of RNA and protein continues and DNA content is doubled but paired dipoid condition exists.

Question 9.
Mention the number of autosomes present in human ovum.
Answer:
22

Question 10.
In which phase of cell division does a centromere divide.
Answer:
Anaphase.

Question 11.
What is autosome?
Answer:
The chromosomes in the cells which are responsible for the determination of the body (somatic) structure and functions are called autosomes.

Question 12.
Write the nitrogen bases of an RNA molecule.
Answer:
Adenine, guanine, cytosine, uracil.

Question 13.
In which type of cell division do the nucleus and cytoplasm divide directly?
Answer:
Amitosis.

Question 14.
What type of sex-chromosomes are found in the cells of human body?
Answer:
x and y.

Question 15.
In which type of cell division spindle fibre is not formed?
Answer:
Amitosis.

Question 16.
How many daughter cells are produced during one mitosis cell division?
Answer:
Two.

Question 17.
By which method cytokinesis occurs in animal cell?
Answer:
Cleavage or by furrowing.

Question 18.
What will happen to a cell if karyokinesis is not followed by cytokinesis? From where do the spindle fibres develop during the cell divison of a plant cell and an animal cell?
Answer:
Spindle fibres are formed from microtubules of nucleoplasm in plant cell. Spindle fibres are formed from astral rays in animal cell.

Question 19.
By which part an Eukaryotic chromosome remains attached with spindle fibre?
Answer:
Centromere.

Question 20.
Mention two differences between DNA and RNA :
Answer:

DNA	RNA
i. Sugar is deoxyribose sugar.	i. Sugar is ribose sugar.
ii. N2 base is thymine.	ii. N2 base is uracil.

Question 21.
What is the function of centromeres telomere?
Answer:
Centromere : Helps in attachment of spindle fibre during cell division. Telomere : Prevents the ends of chromosomes from sticking together.

Question 22.
In the chromosome number in pea plant is 2n = 18, what will be the chromosome number in leaf, pollen grain endosperm nucleus and egg of the plant?
Answer:
Chromosome number in leaf = 18(2n)
Chromorsome number in pollen grain = 9(n)
Chromosome number in endosperm nucleus = 27(3n)

Question 23.
What is cytokinesis?
Answer:
The process of cleavage and separation of the cytoplasm and the final stage of mitosis is known as cytokinesis.

Question 24.
What is mitotic apparatus?
Answer:
The aster, the centrioles and the spindle together make up the structure called mitotic apparatus.

Question 25.
What is the chromosome number in human female gamet?
Answer:
Chromosome number present in human female gamet is 23.

Question 26.
Write two significance of meiosis cell division.
Answer:
i. Meiosis maintains a definite and constant number of chromosome in the cell of a particular species.
ii. In animals meiosis leads to the formation of sexual gamets, the egg ovum and the sperm with haploid number of chromosome.

Question 27.
Which allosomes are present in human male?
Answer:
y

Question 28.
Where is haploid chromosome seen?
Answer:
Germ mother cell.

Question 29.
When is chromosome distinctly visible?
Answer:
Metaphase.