1st PUC Biology Question Bank Chapter 10 Cell Cycle and Cell Division

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Karnataka 1st PUC Biology Question Bank Chapter 10 Cell Cycle and Cell Division

1st PUC Biology Question Bank NCERT Text Book Questions and Answers

Question 1.
What is the average cell cycle span for a mammalian cell?
Answer:
It is significant to note that in the 24-hour average duration of the cell cycle of a human cell or mammalian cells, cell division proper lasts for only about an hour.

Question 2.
Distinguish cytokinesis from karyokinesis.
Answer:

• Karyokinesis: It is a phase in which the division of the nucleus into two daughter nuclei occurs. Separation of daughter chromosomes occurs in this phase. It consists of four substages namely prophase, metaphase, anaphase, and telophase.
• Cytokinesis: It refers to the division of the cytoplasm resulting in two daughter cells.

Question 3.
Describe the events taking place during the interphase.
Answer:
Interphase is divided into three phases viz. G( phase, S phase, and G2 phase.
Gj phase (Gap 1): G( phase corresponds to the interval between mitosis and initiation of DNA replication. During G( phase the cell is metabolically active and continuously grows but does not replicate its DNA.
S phase (Synthesis): S or synthesis phase marks the period during which DNA synthesis or replication takes place. During this time the amount of DNA per cell doubles. If the initial amount of DNA is denoted as 2C then it increases to 4C. However, there is no increase in the chromosome number; if the cell had diploid or 2n number of chromosomes at G|, even after S phase the number of chromosomes remains the same i.e., 2n.
G2 phase (Gap 2): In animal cells, during the S phase, DNA replication begins in the nucleus, and the centriole duplicates in the cytoplasm. During the G2 phase, proteins are synthesised in preparation for mitosis while cell growth continues.

Question 4.
What is the G₀(quiescent phase) of the cell cycle?
Answer:
Some ceils in adult animals which divide occasionally to replace cells that are lost exit the G₁ phase to enter an inactive stage called the quiescent stage (G₀) of the cell cycle. Cells in this stage remain metabolically active but no longer proliferate unless called on to do so by the organism.

Question 5.
Why is mitosis called equational division?
Answer:
Mitosis called equational division because it keeps the chromosome number constant and genetic stability in daughter cells.

Question 6.
Name the stage of the cell cycle at which one of the following events occur:

1. Chromosomes are moved to the spindle equator.
2. Centromere splits and chromatids separate.
3. The pairing between homologous chromosomes takes place.
4. Crossing over between homologous chromosomes takes place.

Answer:

1. Metaphase
2. Anaphase
3. Zygotene
4. Pachytene

Question 7.
Describe the following:
(1) synapsis
(2) bivalent
(3) chiasmata Draw a diagram to illustrate your answer.
Answer:
1. Synapsis: During zygotene, stage chromosomes start pairing together and this process of association is called synapsis.
2. Bivalent: The synaptonemal complex formed by a pair of synapsed homologous chromosomes is called a bivalent or a tetrad.
3. Chiasmata: The beginning of diplotene is recognized by the dissolution of the synaptonemal complex and the tendency of the recombined homologous chromosomes of the bivalents to separate from each other except at the sites of crossovers. These X-shaped structures are called charismata. In oocytes of some vertebrates, diplotene can last for months or years.

Question 8.
How does cytokinesis in plant cells differ from that in animal cells?
Answer:
Due to the presence of a cell wall, cytokinesis in a plant cell is significantly different from that in animal cells. Rather than forming a contractile ring, plant cells construct a cell plate in the middle of the cell. The golgi apparatus releases vesicles containing cell wall materials. These vesicles fuse at the equatorial plane and form a cell plate that represents the middle lamella between the walls of two adjacent cells.

Question 9.
Find examples where the four daughter cells from meiosis are equal in size and where they are found unequal in size.
Answer:
The four daughter haploid cells may or may not be equal in size at the end of meiosis II with telophase II.

Question 10.
Distinguish anaphase of mitosis from anaphase I of meiosis
Answer:

Anaphase of Mitosis	Anaphase I of Meiosis
(a) Centromeres are split at this stage and chromatids separate. (b) The chromosomes are large and thin	(a) Centromeres do not divide at this stage. Homologous chromosomes separate while sister chromatid remains associated at their centromeres. (b) Chromosomes are shorter and thicker

Question 11.
List the main differences between mitosis and meiosis.
Answer:

Mitosis	Meiosis
(a) Mitosis consists of a single division.	(a) Meiosis is a two-phase division.
(b) Mitosis is an equational division. The daughter cell has a same number of chromosomes as that of the parent cell.	(b) The chromosome number in the daughter cell is reduced to half of that in the parent cell.
(c) Mitosis results in growth.	(c) Meiosis results in reproduction.
(d) Mitosis results in two daughter cells.	(d) Meiosis results in four daughter cells.
(e) The daughter cells are similar to that of a parent	(e) The daughter cells vary from their parent cell
(f) Mitosis occurs continuously in somatic cells.	(f) Meiosis occurs in germ cells during garnet genesis.
(g) Mitosis is a simple division	(g) Meiosis is a complex division.

Question 12.
What is the significance of meiosis?
Answer:
The significance of meiosis:

1. It reduces the number of chromosomes to half in the daughter cells.
2. It is a very essential phenomenon in the life cycle of sexually reproducing animals as it restores the fixed number of chromosomes present in the somatic cells, characteristic of the species.
3. Gametes are formed as a result of meiosis. Each gamete possesses half the number of chromosomes present in the somatic cells.
4. It avoids the multiplication of chromosomes and thus maintains the stability and a constant number of chromosomes of the species.
5. During the crossing over the exchange of nuclear material (genes) cause genetic variations within the species. As a result, new combinations of hereditary material are formed.

Question 13.
Discuss with your teacher about

1. haploid insects and lower plants where cell-division occurs, and
2. some haploid cells in higher plants where cell-division does not occur.

Answer:

1. Haploid insect – Honey bee
   haploid lower plants – Spirogyra, Riccia.
2. Male and female gametes.

Question 14.
Can there be mitosis without DNA replication in ‘S’ phase?
Answer:
DNA replication is necessary for cell division and cell division cannot happen without DNA replication.

Question 15.
Can there be DNA replication without cell division?
Answer:
Generally, DNA replication is followed by cell division. But, there can be DNA replication without cell division.

Question 16.
Analyse the events during every stage of cell cycle and notice how the following two parameters change
(i) Number of chromosomes (N) per cell
(ii) Amount of DNA content (C) per cell
Answer:
G1 Phase – 2N 2C
S Phase – 2N 2C
G2 Phase – 4N 4C
M Phase – 2N 2C
2N corresponds to diploid chromosomes whereas 2C corresponds to diploid.

• The number of chromosomes doubles after mitotic cell division and becomes half after meiotic cell division.
• During the S phase the DNA content doubles, but the number of chromosomes remains the same.

1st PUC Biology Question Bank Additional Questions and Answers

1st PUC Biology Question Bank One Mark Questions

Question 1.
What is Karyokinesis? (B’lore North 2005)
Answer:
The division of the nucleus is called karyokinesis.

Question 2.
What is interphase?
Answer:
The nondividing phase of the cell is interphase

Question 3.
In which phase DNA replication takes place?
Answer:
S or synthetic phase.

Question 5.
Mention the substages of Interphase.
Answer:
G₁ stage, ‘S’ stage and G₂ stage.

Question 6.
What is Cytokinesis? (B’lore North, Dharwar .04)
Answer:
Division of cytoplasm is called cytokinesis.

Question 7.
Mention the Substages of Mitosis.
Answer:
Prophase, Metaphase, Anaphase, Telophase, Cytokinesis.

Question 8.
Give two differences between plant and animal cell division.
Answer:

• In-plant cell, Asters are not formed.
  In animal cell Asters are formed.
• In-plant cell, cytokinesis occurs due to the formation of a cell plate.
  In an animal cell, cytokinesis occurs due to the formation of a cleavage furrow.

Question 9
What is kinetochore?
Answer:
The kinetochore is a discoidal area on the chromatid which is the site of attachment of spindle fibre.

Question 10.
What Is genetic crossing over? (B.North. 04)
Answer:
Exchanges of segments between non-sister chromatids of the bivalents are called Genetic crossing over.

Question 11.
What are Chiasmata?
Answer:
The regions where segments of non-sister chromatids of the bivalents are exchanged are called chiasmata.

Question 12.
What is interkinesis?
Answer:
Interkinesis is an interphase between meiosis I and meiosis II.

Question 13.
Define cell cycle.
Answer:
The sequence of events by which a cell duplicates its genome, synthesis the other constituents of the cell, and eventually divides into two daughter cells is termed as the cell cycle.

Question 14.
What percentage of the duration of the cell cycle does interphase last?
Answer:
More than 95%.

Question 15.
What happens during the ‘S’ phase In animal cells?
Answer:
During the ‘S’ phase in animal cells, DNA replication begins in the nucleus, and the centriole duplicates in the cytoplasm.

Question 16.
Name the two major types of cell division.
Answer:
Mitosis and meiosis.

Question 17.
What is a metaphase plate?
Answer:
The plane of alignment of the chromosomes at metaphase is referred to as the metaphase plate.

Question 18.
When do the centromeres of chromosomes divide in a cell of the root tip?
Answer:
During anaphase of mitosis.

Question 19.
Name the stage of mitosis, when chromosomes start their poleward movement.
Answer:
Anaphase.

Question 20.
When does the nucleolus reappear during mitosis?
Answer:
Telophase.

Question 21.
What is a cell plate?
Answer:
The formation of the new cell wall begins with the formation of a simple precursor, called the cell plate that represents the middle lamella between the walls of two adjacent cells.

Question 22.
Define meiosis.
Answer:
The specialized kind of cell division that reduces the chromosome member by half resulting in the production of haploid daughter cells is called meiosis.

Question 23.
What indicates the beginning of diplotene?
Answer:
The beginning of diplotene is recognised by the dissolution of the synaptonemal complex and the tendency of the recombined homologous chromosomes to separate from each other.

Question 24.
Name the last state of prophase I and what marks this stage?
Answer:
Diakinesis is the last stage of prophase I and it is marked by the terminalisation of chiasmata.

Question 25.
When does the actual reduction in the number of chromosomes take place during meiosis?
Answer:
Anaphase I.

Question 26.
What is Interkinesis?
Answer:
The stage between the two meiotic divisions (Meiosis I and Meiosis II) is called interkinesis.

Question 27.
Name the stage of all division to study the chromosome morphology.
Answer:
Metaphase.

1st PUC Biology Question Bank Two Marks Questions

Question 1.
Write the three processes which take place in interphase.
Answer:
Three processes which take place in interphase are:

• The replication of DNA and the synthesis of histones and nuclear proteins.
• Division of centriole to form two new centrioles which lie at a right angle to each other.
• The synthesis of the energy-rich compounds to provide energy for mitosis.

Question 2.
Name any four stages of prophase of meiosis (M.Q.P., Mandya. 05)
Answer:
Leptotene, Zygotene
Pachytene, Diplotene & Diakinesis.

Question 3.
Bring out any four differences between mitosis and meiosis. (Hassan. 05, D.K. 2008)
Answer:

• Mitosis is seen in somatic cells, whereas Meiosis is seen in germ cells.
• Mitosis is an equational division, whereas Meiosis is a reductional division.
• In mitosis no crossing over, whereas in miosis crossing over between non-sister chromatids is seen.
• In mitosis one cell produces two cells with the same chromosome number, whereas In meiosis one cell produces four haploid cells

Question 4.
Write any 2 differences between Mitosis and Meiosis.
Answer:

• Mitosis consists single nuclear divisions.
  Meiosis consists of two nuclear divisions.
• In mitosis crossing over is absent.
  In Meiosis crossing over is present.

Question 5.
Mention the substages of Meiosis
Answer:

• Proohase II
• Metaphase II
• Anaphase II
• Telophase II
• cytokinesis.

Question 6.
Define Ceil Cycle. Mention two main stages of Ceil Cycle.
Answer:
The series of events occurring in a growing cell that occurs between the formation of cell and its division into daughter cells is called cell cycle. Two main stages are Interphase and M. Phase.

Question 7.
Mention the differences between G and G₂ phase of Interphase.
Answer:

G1 phase	G2 phase
(a) It is the first substage of interphase that follows cytokinesis (b) The Cell is metabolically active and contiguously grows but does not replicate its DNA. (c)  Certain cells may stop dividing and enter G0 phase	(a)  It is the last substage of interphase which is followed by M-phase (b)  Proteins are synthe­sized in preparation for mitosis while cell growth continues (c)  All cells entering G2 phase continue with the M-phase

Question 8.
What are kinetochores? What is their function?
Answer:
Kinetochores are small disc-shaped structures at the surface of centromeres. They serve as the binding site for the spindle fibres to the centromeres of chromosomes.

Question 9.
Mention the events that occur during diakinesis.
Answer:
The events that occur during diakinesis:

• There is terminalisation of chiasmata.
• The chromosomes are fully condensed.
• The assembling of the meiotic spindle is initiated.
• The nucleolus and nuclear membrane break down and disappear completely by the end of diakinesis.

Question 10.
What is crossing over? Name the enzyme responsible for it.
Answer:
Crossing over is defined as the exchange of equivalent segments between non-sister chromatids of homologous chromosomes and the exchange of genetic material between them. The enzyme responsible for crossing over is recombinase.

Question 11.
Mention the events that occur during diakinesis.
Answer:
During diakinesis, there is terminalisation of chiasmata. The chromosomes are fully condensed and the meiotic spindle is assembled to prepare the homologous chromosomes for separation. The nucleolus disappears and the nuclear envelope breaks down.

Question 12.
Mention the key features of metaphase in mitosis.
Answer:

• Spindle fibres attach to kinetochores of chromosomes
• Chromosomes are moved to the spindle equator and get aligned along with the metaphase plate through spindle fibres to both poles.

Question 13.
What is syncytium? Give an example.
Answer:
In some organisms karyokinesis is not followed by cytokinesis as a result of which multinucleate condition arises leading to the formation of the syncytium.
E.g: liquid endosperm in coconut.

Question 14.
How does metaphase I differ from metaphase?

Metaphase I	Metaphase II
(a)  The homologous pairs of chromosomes are arranged in two rows near the centre of the spindles. (b) There no metaphasic plate formed (c) The arms of the chromosomes are at spindle fibres	(a)  Centromeres of all the chromosomes are arranged in a single row at the centre of the spindles (b) A metaphase plate is formed (c)  The arms of the chromosomes are parallel to the fibres.

Question 15.
Name the four substages of prophase I.
Answer:

• Leptotene
• Zygotene
• Pachytene
• diplotene

1st PUC Biology Question Bank Three Marks Questions

Question 1.
What is the role of the centrosome with centriole?
Answer:
The centrosome with centriole plays a very important role in mitosis and meiosis. It forms spindle-shaped fibers attached to 10 chromosomes and these place chromosomes to the equator and then to the poles. Without the centrosome with centriole, these processes were not able to be performed in the cell.

Question 2.
Describe the events in the telophase of mitosis.
Answer:
Telophase is the final stage of mitosis. The events that happen in telophase are:-

• Chromosomes cluster at opposite spindle poles and their identity is lost as discrete elements.
• Nuclear envelop assembles around the chromosome cluster.
• Nucleolus, Golgi complex and ER reform.

Question 3.
How and why chromosome number is maintained the same in the cell mitotic division.
Answer:
The chromosomes in the prophase stage of mitosis are 2N, which later becomes 4N. Then in anaphase I, the chromosomes segregate, followed by nuclear and cell division. Which restores the chromosome number to 2N.

Question 4.
Diagrammatically show the stages of Meiosis I.
Answer:

Question 5.
Diagrammatically shows the stages of Meiosis I.
Answer:

1st PUC Biology Question Bank Five Marks Questions

Question 1.
Explain Anaphase and Telophase of Mitosis
Answer:
Anaphase:

• The centromere of each chromosome splits. So that chromatids separate.
• The separated chromatids along with the centromeres get pulled to the opposite poles. Such movement of chromatids takes place by the shortening of chromosomal fibres. The Anaphasic chromosomes appear V, L, J or I shaped.

Telophase:

• Condensed chromosomes begin to decondense, become thin and produce the chromatin network.
• Spindle fibers, asters, disappear.
• Nucle I membrane, nucleoli are formed. So at the end cell consists of two nuclei one at each pole

Question 2.
With neat labelled diagrams explain Meiosis I (Gulbarga, Belgaum, B.South 04, D.K. 07)
Answer:
The first meiotic division is reductional division so that two haploid cells are formed.
Meiosis I consists I Karyokinesis I: It has the following stages;

A. Prophase:
It lasts for a long period and studied under the following substages.
(Shimoga. 06)

(a) Leptotene following is the characteristic of leptotene
Chromosomes are long, thin and they are double-stranded each chromosome appears as a string of beads. Such beads are called chromomeres.

(b) Zygotene

• Homologous chromosomes come to lie side by side, closely applied at every point this process of pairing is called Synapsis.
• Each pair is called bivalent and each bivalent consists of 2 chromatids, so-called tetrad.
• The two chromatids of the same chromosome are called sister chromatids and chromatids belonging to two different chromosomes are called non-sister chromatids.

(c) Pachytene :

• Two non-sister chromatids of each tetrad get coiled around each other and exchanges segments
• This process is called genetic crossing over. It results in the recombination of genes. Crossing over takes place by breaking and reunion of chromatids.
• The points where exchanges have occurred appear X – shaped structure. It is called chiasmata.

(d) Dipiotene

• Chromosomes are more condensed
• The attraction between homologous chromosomes disappears, but repulsion begins.
• Repulsion produces chain like 8 – shaped or o shaped bivalents.
• Repulsion results in the criminalization of chiasmata and finally disappears.

(e) Diakinesis:
Nucleolus disappear, nuclear membranes disappears and each bivalent shows four chromatids.

(B) Metaphase
(i) Paired chromosomes ar-range at the equatorial plane of the spindle and spindle fibres become attached to the centromeres of each chromosome.

(C) Anaphase
Spindle fibres contract so bivalent move towards the opposite poles of the spindle. The separated chromosomes are called univalents. The two centromeres of a homologous pair move towards the opposite poles along with the chromosomes.

(D) Telophase :

• Chromosomes reach the poles. They uncoil and become thin and long thread-like.
• Nuclear membrane and Nucleoli reappear:
• Cytokinesis I
• A constriction develops in the middle of the cell which becomes deep and the cytoplasm is divided into two equal parts.

Question 3.
With neat labelled diagrams explain Mitosis In an Animal Cell. (Shimoga, Chikmagalore, Dharwar, Bijapur 2004, B’Iore North, Tumkur, Kolar, Mandya 2005)
Ans:
There are two processes. They are
(1) Karyokinesis.
(2) Cytokinesis

(1) Karyokiriesis: It is divided into the following sub-stages.

• The duplicated chromosomes undergo condensation (become Short and thick).
• Each chromosome has two chromatids and remains attached to each other at the region of the centromere.
• Centrioles are duplicated and begin to move towards the other pole of the cell.
• Aster begins to appear around each centriole.
• Spindle fibers begin to appear.
• Nuclear membranes and Nucleolus disappear.

• Spindle fibres are completely formed.
• Chromosomes are highly condensed and they arrange at the equator.
• Spindle fibre attached to the centromere and arms project in a different direction.

The spindle fibers become short and two chromatids of each chromosome separate and move away from the equator to the opposite poles. The moving chromosomes exhibit different shapes like V or J shapes.

The daughter chromosomes arrived at the poles start uncoiling become thin. The nuclear membrane and nucleolus reappear around the chromosome at each pole. Spindle fibres disappear.

(ii) Cytokinesis: A furrow develops in the middle of the cell which depends at the centre and divides the cytoplasm into two equal parts.

Question 4.
Draw a neat labelled diagram of the Metaphase chromosome and explain any four parts.
Answer:
1) Karyokiriesis: It is divided into the following sub-stages.

• The duplicated chromosomes undergo condensation (become Short and thick).
• Each chromosome has two chromatids and remains attached to each other at the region of the centromere.
• Centrioles are duplicated and begin to move towards the other pole of the cell.
• Aster begins to appear around each centriole.
• Spindle fibers begin to appear.
• Nuclear membranes and Nucleolus disappear.

• Spindle fibres are completely formed.
• Chromosomes are highly condensed and they arrange at the equator.
• Spindle fibre attached to the centromere and arms project in a different direction.

The spindle fibers become short and two chromatids of each chromosome separate and move away from the equator to the opposite poles. The moving chromosomes exhibit different shapes like V or J shapes.

The daughter chromosomes arrived at the poles start uncoiling become thin. The nuclear membrane and nucleolus reappear around the chromosome at each pole. Spindle fibres disappear.

(ii) Cytokinesis: A furrow develops in the middle of the cell which depends at the centre and divides the cytoplasm into two equal parts.

Question 5.
Describe the Zygotene and Pachytene stage of Meiosis. (D. Kannada 2009)
Answer:
Zygotene:

• Homologous chromosomes come to lie side by side, closely applied at every point this process of pairing is called Synapsis.
• Each pair is called bivalent and each bivalent consists of 2 chromatids, so-called tetrad.
• The two chromatids of the same chromosome are called sister chromatids and chromatids belonging to two different chromosomes are called non-sister chromatids.

Pachytene:

• Two non-sister chromatids of each tetrad get coiled around each other and exchanges segments
• This process is called genetic crossing over. It results in the recombination of genes. Crossing over takes place by breaking and reunion of chromatids.
• The points where exchanges have occurred appear X – shaped structure. It is called chiasmata.

Question 6.
When does each of the following occur in mitosis?

1. The nuclear membrane reappears
2. The chromosomes are the thickest and shortest
3. Centromere divides into two
4. Chromosomes begin to coil
5. The nuclear membrane disappears

Answer:

1. Telophase.
2. Metaphase
3. Anaphase
4. Prophase
5. Prophase.

Question 7.
Give the specific scientific term for the following:

1. The period between two successive mitotic divisions
2. Process of all division by which chromosome member is halved.
3. Nuclear division in mitosis
4. Phase in the cell cycle when proteins and RNA are synthesized
5. The point at which two sister chromatids are held together.

Answer:

1. Interphase
2. Meiosis
3. Karyokinesis
4. Interphase
5. Centromere

Question 8.
March the following:
(a) Protein Synthesis – (i) Meiosis
(b) Equational division – (ii) Zygotene
(c) Reductlonal division – (iii) G₂ phase
(d) Synaptonemal complex – (iv) diplotene
(e) Chlasmata – (v) Mitosis
Answer:
(a) – (iii)
(b) – (v)
(c) – (i)
(d) –  (ii)
(e) –  (iv)