Students get through the TN Board 11th Bio Botany Important Questions Chapter 7 Cell Cycle which is useful for their exam preparation.
TN State Board 11th Bio Botany Important Questions Chapter 7 Cell Cycle
Answer the following short answers.
Question 1.
Who coined the word “Cell” and “protoplasm”?
Answer:
Robert Hooke, Jan Evangelista purkyne (J.E.Purkinje)
Question 2.
Mentions any two roles of the nucleus.
Answer:
- Control activities of the cell.
- Genetic information copied from cell to cell while the cell divides.
Question 3.
Define the term haploid.
Answer:
In meiosis, the daughter cells contain half the number of chromosomes of the parent cell and are known as a haploid state (n).
Question 4.
Define the term Cytokinesis.
Answer:
Whichever division takes place, it is normally followed by division of the cytoplasm to form separate cells, called cytokinesis.
Question 5.
What is C – Value?
Answer:
C-Value is the amount in picograms of DNA contained within a haploid nucleus.
Question 6.
What do you know about clone dolly?
Answer:
Since the DNA of cells in G0, does not replicate. The researcher is able to fuse the donor cells from a sheep’s mammary glands into G0 state by culturing in the nutrient-free state. The G0 donor nucleus synchronized with the cytoplasm of the recipient egg, which developed into the clone, Dolly.
Question 7.
Define maturation promoting factor (MPF).
Answer:
One of the proteins synthesized only in the G2 period is known as Maturation Promoting’Factor (MPF). It brings about the condensation of interphase chromosomes into the mitotic form.
Question 8. Define Amitosis.
Answer:
Amitosis is also called direct or incipient cell division. Here there is no spindle formation and chromatin material does not condense.
Question 9.
Mention two drawbacks of amitosis.
Answer:
- Causes unequal distribution of chromosomes.
- Can lead to abnormalities in metabolism and reproduction.
Question 10.
Explained closed mitosis.
Answer:
In closed mitosis, the nuclear envelope remains intact and chromosomes migrate to opposite poles of a spindle within the nucleus.
Question 11.
How does an aster form?
Answer:
In an animal cell, the centrioles extend a radial array of microtubules towards the plasma membrane when they reach the poles of the cell. This arrangement of microtubules is called an aster. Plant cells do not form asters.
Question 12.
What do you mean by anaphase-promoting complex cyclosome (APC/C)
Answer:
A ubiquitine ligase is activated called the anaphase-promoting complex cyclosome (APC/C) leads to degradation of the key regulatory proteins at the transition of metaphase to anaphase. APC is a cluster of proteins that induces the breaking down of cohesion proteins which leads to the separation of chromatids during mitosis.
Question 13.
List out various stages of prophase I of Meiotic cell division
Answer:
Leptotene, zygotene, pachytene, diplotene and diakinesis.
Question 14.
Define Chiasmata.
Answer:
The homologous chromosomes remain attached at one or more points where crossing over has taken place. These points of attachment where ‘X’ shaped structures occur at the sites of crossing over is called Chiasmata.
Question 15.
What is meant by metaphase plate?
Answer:
Bivalent (pairs of homologous chromosomes) aligned at the equator of the cell known as the metaphase plate.
Question 16.
Define interkinesis.
Answer:
The stage between the two meiotic divisions is called interkinesis which is short-lived.
Question 17.
Mention any two of the significance of meiosis.
Answer:
This maintains a definite constant number of chromosomes in organisms. Crossing over takes place and the exchange of genetic material leads to variations among species. These variations are the raw materials for evolution. Meiosis leads to genetic variability by partitioning different combinations of genes into gametes through independent assortment.
Question 18.
Explain the term ‘Mitogen’.
Answer:
The factors which promote cell cycle proliferation are called mitogen. Plant mitogens include gibberellin, ethylene, Indole acetic acid, kinetin. These increase the mitotic rate.
Question 19.
Define Anastral condition in cell division.
Answer:
This is present only in plant cells! No asters or centrioles are formed only spindle fibers are formed during cell division.
Question 20.
Explain Amphiastral condition.
Answer:
Aster and centrioles are formed at each pole of the spindle during cell division. This is found in animal cells.
Answer In brief.
Question 1.
Enumerate any three important features of the chromosome.
Answer:
- The shape of the chromosome is specific: The long, thin, lengthy structured chromosome contains a short, constricted region called a centromere. A centromere may occur anywhere along the chromosome, but it is always in the same position on any given chromosome.
- The number of chromosomes per species is fixed: for example, the mouse has 40 chromosomes, the onion has 16 and humans have 46.
- Chromosomes occur in pairs: The chromosomes of a cell occur in impairs, called homologous pairs. One of each pair come originally from each parent, eg. human has 46 chromosomes,
- coming originally from each parent in the process of sexual reproduction.
Question 2.
Tabulate the time duration in hours of the different phases of the cell cycle.
Answer:
Phase | Time duration (in hrs) |
G1 | 11 |
S | 8 |
G2 | 4 |
M | 1 |
Question 3.
Explain G1 phase of cell cycle.
Answer:
The first gap phase-2 C amount of DNA in cells of G1. The cells become metabolically active and grow by producing proteins, lipids, carbohydrates, and cell organelles including mitochondria and endoplasmic reticulum. Many checkpoints control the cell cycle. The checkpoint called the restriction point at the end of G1 determines a cell’s fate whether it will continue in the cell cycle and divide or enter a stage called G0 as a quiescent stage and probably as specified cell or die. Cells are arrested in G1 due to:
- Nutrient deprivation.
- Lack of growth factors or density-dependent inhibition.
- Undergo metabolic changes and enter into G0 state.
Biochemicals inside cells activate cell division. The proteins called kinases and cyclins activate, genes and their proteins to perform cell division. Cyclins act as major checkpoint which operates in G1 to determine whether or not a cell divides.
Question 4.
Distinguish between Karyokinesis and cytokinesis.
Answer:
Karyokinesis | Cytokinesis |
Involves division of the nucleus. | Involves division of cytoplasm. |
The nucleus develops a constriction at the center and becomes dumbell shaped. | Plasma membrane develops a constriction along with nuclear constriction. |
Constriction deepens and divides the nucleus into two. | It deepens centripetally and finally divides the cell into two cells. |
Question 5.
Describe the prophase of Mitotic cell division.
Answer:
- Prophase is the longest phase in mitosis. Chromosomes become visible as long thin thread-like structure, condenses to form compact mitotic chromosomes. In-plant cells initiation of spindle fibers takes place, the nucleolus disappears. The nuclear envelope breaks down. Golgi apparatus and endoplasmic reticulum are not seen.
- In the animal cell, the centrioles extend a radial array of microtubules towards the plasma membrane when they reach the poles of the cell. This arrangement of microtubules is called an aster. Plant cells do not form asters.
Question 6.
How Do you calculate the length of the S period?
Answer:
A Culture of animal cells in which the cell cycles were asynchronous was incubated with 3H-Thymidine for 10 minutes. Autoradiography showed that 50% of the cells were labeled. If the cell cycle time (generation time) was 16 hrs how long was the S period?
Length of the S period Fraction of cells in DNA replication x generation time
Length of the S period == 0.5 x 16 hours = 8 hours
Question 7.
Explain the process of cytokinesis in plant cells.
Answer:
Division of the cytoplasm often starts during telophase. In plants, cytokinesis cell plate grows from center towards lateral walls – centrifugal manner of cell plate formation. Phragmoplast contains microtubules, actin filaments, and vesicles from the Golgi apparatus and ER. The Golgi Vesicles contain carbohydrates such as pectin, hemicellulose which move along the microtubule of the phragmoplast to the equator fuse, forming a new plasma membrane arid the materials which are placed their becomes new cell wall. The first stage of cell wall construction is a line dividing the newly forming cells called a cell plate. The Cell plate eventually stretches right across the cell forming the middle lamella. Cellulose builds up on each side of the middle lamella to form the cell walls of two new plant cells.
Question 8.
Explain the sequences of Anaphase I Telophase I in Meiotic cell division.
Answer:
Anaphase I: Homologous chromosomes are separated from each other. Shortening of spindle fibers takes place. Each homologous chromosome with its two chromatids and undivided centromere move towards the opposite poles of the cells. The actual reduction in the number of chromosomes takes place at this stage. Homologous chromosomes which move to the opposite poles are either 1 paternal or maternal in origin. Sister chromatids remain attached with their centromeres.
Telophase I: Haploid set of chromosomes are present at each pole. The formation of two daughter cells, each with the haploid number of chromosomes. Nuclei are reassembled. Nuclear envelope forms around the chromosome and the chromosomes become uncoiled. Nucleolus reappears.
Question 9.
Give the differences between mitosis in plant and animal cells.
Answer:
Plants | Animals |
Centrioles are absent. | Centrioles are present. |
Asters are not formed. | Asters are formed. |
Cell division involves the formation of a cell plate. | Cell division involves furrowing and cleavage of the cytoplasm. |
Occurs mainly at meristem. | Occurs in tissues throughout the body. |
Question 10.
What is Endomitosis? Explain with example.
Answer:
The replication of chromosomes in the absence of nuclear division and cytoplasmic division resulting in numerous copies within each cell is called endomitosis. Chromonema does not separate to form chromosomes but remains closely associated with each other. The nuclear membrane does not rupture. So no spindle formation. It occurs notably in the salivary glands of Drosophila and other flies. Cells in these tissues contain giant chromosomes (polyteny), each consisting of thousands of intimately associated, or synapsed, chromatids, eg. Polytene chromosome.
Answer In detail.
Question 1.
Draw and label the events of the cell cycle.
Answer:
Question 2.
Draw the schematic diagram of anaphase-promoting complex cyclosome and explain briefly.
Answer:
A ubiquitine ligase is activated called the anaphase-promoting complex cyclosome (APC/C) leads to degradation of the key regulatory proteins at the transition of metaphase to anaphase. APC is a cluster of proteins that induces the breaking down of cohesion proteins which leads to the separation of chromatids during mitosis.
Question 3.
Explain the events that take place at metaphase and anaphase stages of somatic cell division – with diagram.
Answer:
Metaphase: Chromosomes (two sister chromatids) are attached to the spindle fibers by kinetochore of the centromere. The spindle fibers is made up of tubulin. The alignment of the chromosome into the compact group at the equator of the cell is known as the metaphase plate. This is the stage where chromosome morphology can be easily studied.
The kinetochore is a DNA-Protein complex present in the centromere DNA where the microtubules are attached. It is a trilaminar disc-like plate.
The spindle assembly checkpoint decides the cell to enter anaphase.
For diagram refer to Figure 7.2 (Metaphase only).
Anaphase: Each chromosome split simultaneously and two daughter chromatids begin to migrate towards two opposite poles of a cell.
Each centromere splits longitudinally into two, freeing the two sister chromatids from each other. Shortening of spindle fiber and longitudinal splitting of centromere creates a pull that divides the chromosome into two halves.
Each half receives two chromatids (that is sister chromatids are separated). When the sister chromatids separate the actual partitioning of the replicated genome is complete.
For diagram refer to Figure 7.2 (Anaphase only).
Question 4.
Explain the different stages of prophase I of meiotic cell division.
Answer:
- Prophase I: Prophase I is of longer duration and it is divided into 5 substages – Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.
- Leptotene: Chromosomes are visible under a light microscope. Condensation of chromosomes takes place. Paired sister chromatids begin to condense.
- Zygotene: Pairing of homologous chromosomes takes place and it is known as synapsis. Chromosome synapsis is made by the formation of the synaptonemal complex. The complex formed by the homologous chromosomes is called bivalent (tetrads).
- Pachytene: At this stage, bivalent chromosomes are clearly visible as tetrads. Bivalent of meiosis I consist of 4 chromatids and 2 centromeres. Synapsis is completed and, recombination nodules appear at a site where crossing over takes place between non-sister chromatids of the homologous chromosome. Recombination of homologous chromosomes is completed by the end of the stage but the chromosomes are linked at the sites of crossing over. This is mediated by the enzyme recombinase.
- Diplotene: Synaptonemal complex disassembled and dissolves, the homologous chromosomes remain attached at one or more points where crossing over has taken place.
These points of attachment where ‘X’ shaped structures occur at the sites of crossing over is called Chiasmata. - Chiasmata are chromatin structures at sites where recombination has been taken place. They are specialized chromosomal structures that hold the homologous chromosomes together.
Sister chromatids remain closely associated whereas the homologous chromosomes tend to separate from each other but are held together by chiasmata. This substage may last for days or years depending on the sex and organism. - The chromosomes are very actively transcribed in females as the egg stores up materials for use during embryonic development. In animals, the chromosomes have prominent loops called the lampbrush chromosome.
- Diakinesis: Terminalisation of chiasmata. Spindle fibers assemble. The nuclear envelope breaks down. Homologous chromosomes become short and condensed. Nucleolus disappears.
Question 5.
Enumerate the differences between mitosis and meiosis.
Answer:
Mitosis | Meiosis |
One division | Two divisions |
A number of chromosomes remain the same. | The number of chromosomes is halved. |
Homologous chromosomes line up separately on the metaphase plate. | Homologous chromosomes line up in pairs at the metaphase plate. |
Homologous chromosome do not pair up | Homologous chromosomes pair up to form bivalent. |
Chiasmata do not form and crossing over never occurs. | Chiasmata form and crossingover occurs. |
Daughter cells are genetically identical. | Daughter cells are genetically different from the parent cells. |
Two daughter cells are formed. | Four daughter cells are formed. |
Question 6.
Draw and label the various stages of mitosis cell division.
Answer:
Choose the correct answer.
1. The word cell coined by:
(a) Robert brown
(b) Leeuwenhoek
(c) Anton
(d) Robert Hooke
Answer:
(d) Robert Hooke
2. Which of the following is incorrect about the role of the nucleus?
(a) Control activities of the cell
(b) Genetic information copied from cell to cell
(c) Gametic cells fused together in sexual reproduction
(d) Characters passed on to new individuals
Answer:
(c) Gametic cells fused together in sexual reproduction
3. Match the following with phase and time duration:
Phase | Time duration (in hrs) |
G1 | 11 |
S | 8 |
G2 | 4 |
M | 1 |
(a) (i)-(c), (ii)-(a), (iii)-(d), (iv)-(b)
(b) (i)-(c), (ii)-(b), (iii)-(d), (iv)-(a)
(c) (i)-(a), (ii)-(c), (iii)-(d), (iv)-(b)
(d) (i)-(b), (ii)-(d), (iii)-(a), (iv)-(c)
Answer:
(a) (i)-(c), (ii)-(a), (iii)-(d), (iv)-(b)
4. Name the types of nuclear divisions?
(a) Mitosis
(b) Mitosis and Meiosis
(c) A Mitosis
(d) Meiosis
Answer:
(b) Mitosis and Meiosis
5. The checkpoint is otherwise called:
(a) Important point
(b) collecting point
(c) restriction point
(d) Controlling point
Answer:
(c) restriction point
6. In S phase DNA count increases from 2C to:
(a) 3C
(b) 4C
(c) 5C
(d) 6C
Answer:
(b) 4C
7. Which of the following, Microtubules are formed?
(a) G0
(b) G1
(c) S
(d) G2
Answer:
(d) G2
8. Which animal regenerates the parts of its body?
(a) starfish
(b) amoeba
(c) shark
(d) jellyfish
Answer:
(a) starfish
9. Pick the incorrect statement of the significance of meiosis:
(a) maintain a definite constant number of chromosome
(b) Adaption of an organism to various stress
(c) crossing over takes place
(d) The chromosome number increases in the Organism.
Answer:
(d) The chromosome number increases in the Organism.
10. Which one of the following is not a mitotic poison?
(a) Cyanide
(b) A zide
(c) 2, 4, dinitrophenol
(d) Polyamines
Answer:
(d) Polyamines
11. Insulin and steroid hormones are examples of:
(a) Inhibiting factors
(b) Growth factors
(c) Limiting factors
(d) Synthetic factors
Answer:
(b) Growth factors
12. Identify the correct statement for equational division:
(a) The number of chromosomes in the parent and daughter cells remains the same
(b) Chromosome in the parent and daughter are different
(c) Double the number of chromosomes
(d) It depends upon the division
Answer:
(a) The number of chromosomes in the parent and daughter cells remains the same
13. The number of chromosomes in humans are:
(a) 36
(b) 40
(c) 46
(d) 16
Answer:
(c) 46
14. The chromosomes of a cell occur in pairs called:
(a) haploid pair
(b) homologous pair
(c) diploid pair
(d) Tetraploid
Answer:
(b) homologous pair
15. The amount in picograms of DNA contained within a haploid nucleus is called:
(a) B-value
(b) X – value
(c) Y-value
(d) C – value
Answer:
(d) C – value
16. In meiosis, the daughter cells contain half the number of chromosomes of the parent cell and is known as:
(a) Triploid
(b) Haploid
(c) Tetraploid
(d) Diploid
Answer:
(b) Haploid
17. The major checkpoint which operates in G1 to determine whether or not a cell divides is:
(a) Kinase
(b) protease
(c) cyclins
(d) pepsin
Answer:
(c) cyclins
18. A cell division in which no spindle formation and non condensation of chromatin material is called:
(a) Mitosis
(b) Amitosis
(c) Meiosis
(d) None of the above
Answer:
(b) Amitosis
19. Karyokinesis involves in:
(a) division of cytoplasm
(b) division of cells
(c) division of nucleus
(d) none of the above
Answer:
(c) division of nucleus
20. The sequence of stages of mitotic cell division is as follows:
(a) Metaphase, Anaphase, Prophase and Telophase
(b) Telophase, Anaphase, Prophase and Metaphase
(c) Prophase, Anaphase, Telophase and metaphase
(d) Prophase, Metaphase, Anaphase and Telophase
Answer:
(d) Prophase, Metaphase, Anaphase and Telophase
21. The longest phase in mitosis is:
(a) Metaphase
(b) Telophase
(c) Prophase
(d) Anaphase
Answer:
(c) Prophase
22. The cells, which do not form asters during cell division are:
(a) Animal cells
(b) Plant cells
(c) Virus
(d) None of the above
Answer:
(b) Plant cells
23. Mitosis cell division occurs during:
(a) Cogenesis
(b) Gametogenesis
(c) Somatic growth
(d) Spermatogenesis
Answer:
(c) Somatic growth
24. The Golgi vesicles contain carbohydrates such as:
(a) Pectin
(b) Actin
(c) Glucose
(d) Fructose
Answer:
(a) Pectin
25. A sexual reproduction is prominent is:
(a) Starfish
(b) Dolphin
(c) Yeast
(d) Delonix regia
Answer:
(c) Yeast
26. Synapsis takes place in meiosis during:
(a) Pachytene
(b) Metaphase
(c) Diplotene
(d) Zygotene
Answer:
(d) Zygotene
27. Chiasmata is the point where:
(a) Grossing over takes place
(b) Nuclear division takes place
(c) Cytokinesis occur
(d) Nucleolus disappears
Answer:
(a) Grossing over takes place
28. The random distribution of homologous chromosomes in a cell in metaphase I of meiotic cell division is called:
(a) Segregation
(b) Independent assortment
(c) Linkage
(d) None of the above
Answer:
(b) Independent assortment
29. The stage between two meiotic divisions is called:
(a) Karyokinesis
(b) cytokinesis
(c) Interphase
(d) Interkinesis
Answer:
(d) Interkinesis
30. The factors which promote cell cycle proliferation is called:
(a) Mitotic poison
(b) action
(c) mitogen
(d) recombinase
Answer:
(c) mitogen