Odisha State Board CHSE Odisha Class 11 Biology Solutions Chapter 10 Cell Division Cycle Textbook Questions and Answers.
CHSE Odisha 11th Class Biology Chapter 10 Question Answer Cell Division Cycle
Cell Division Cycle Cells Class 11 Questions and Answers CHSE Odisha
Very Short Answer Type Questions
Multiple choice questions
Question 1.
During cell division, the replication of DNA occurs during
(a) M-phase
(b) S-phaase
(c) G-phase
(d) Prophase
Answer:
(b) S-Phase
Question 2.
In male flowers, meiosis is seen in
(a) sepals
(b) androecium
(c) petals
(d) gynoecium
Answer:
(b) androecium
Question 3.
From every meiocyte the spores formed is (are)
(a) one
(b) two
(c) four
(d) eight
Answer:
(c) four
Express in one word
Question 4.
The pairing of homologous chromosome.
Answer:
Synapsis
Question 5.
The points of exchange of chromosome segments.
Answer:
Crossing over
Question 6.
The process of end of exchange of chromosomal segments.
Answer:
Terminalisation
Question 7.
The process of division of cytoplasm into two cells.
Answer:
Cytokinesis
Question 8.
Cells with multiple chromosome numbers.
Answer:
Polyploids
Fill in the blanks
Question 9.
………… can disrupt spindle fibre and is also used to induce polyploidy.
Answer:
Colchicine
Question 10.
During the chromosomes are aligned at the equatorial plate.
Answer:
Metaphase
Question 11.
Where the cells are not separated by cell walls and nuclei lie scattered are called condition.
Answer:
Coenocytic
Question 12.
In yeasts, the cells divide by ………….. .
Answer:
budding
Question 13.
During pachytene …………. chromosomes pair.
Answer:
homologous
Short Answer Type Question
Question 14.
Write short notes on
(a) Control of cell cycle
Answer:
The cell cycle is controlled by certain proteins at certain points in a cell cycle called check points. These proteins are called Cyclin-dependent protein kinases (Cdks) and cyclins.
A Cdk is infact an enzyme that adds negatively charged phosphate groups to other molecules through phosphorylation process. This signals the cell to enter the next stage of cell cycle. But, Cdks are dependent on cyclins for their activation.
Cyclins are activating proteins that bind to Cdks to form a cyclin-Cdk complex. The exit from a particular phase of cell cycle takes place when cyclin gets degraded thereby deactivating Cdks.
(b) Chromosomal pairing
Answer:
Chromosomal pairing It occurs during zygotene of Prophase-I during meiois. During this process, the homologous chromosomes pair by the process called synapsis and the connecting material is called synaptonemal complex. The chromosomal pairs are called bivalents.
(c) S-phase of cell cycle
Answer:
S (Synthesis)-phase It is the phase in which actual synthesis or replication of DNA takes place. The overall amount of DNA doubles per cell, but no increase in chromosome number takes place during this phase. Therefore, if the initial amount of DNA is 2C, it will become 4C at the end of S-phase.
In case of animal cell, during S-phase DNA replication begins inside the nucleus while, the duplication of centrioles takes place in the cytoplasm.
(d) Anaphase of mitosis
Answer:
It is known to be the shortest duration phase, i.e., only of 2-3 min and is also very simple stage. At the beginning of this phase, splitting of chromosomes (that are already arranged at metaphase plate) takes place.
The two daughter chromatids now become the chromosomes of future daughter nuclei and start migrating towards the opposite poles along the path of their chromosome fibres.
(e) Amitosis
Answer:
It refers to the type of division that operate differently from the pattern followed by mitosis for, e.g.
(i) In some algal and fungal forms there is direct division of the cell nuclei.
(ii) In some cases, there is free nuclear division in which the cells do not possess cell walls and several nuclei are found scattered in the cytoplasm of large cells. These cells are called coenocytic cells.
(iii) In yeast, the cells divide by budding. The protoplast of parent cell bulges out through which a daughter nuclei migrates later to form a daughter cell.
Long Answer Type Questions
Question 15.
Describe the prophase-I of meiosis with suitable diagrams. What is the significance of this type of divison?
Answer:
Prophase-I
It is considered to be the most complicated and prolonged phase as compared to the similar stage in mitosis.
This phase is further subdivided into five subphases on the basis of chromosomal behaviour, i.e., leptotene, zygotene, pachytene, diplotene and diakinesis.
(i) Leptotene (Thin thread)
It is known to be the very first stage of meiotic division following the interphase.
Following features are seen during this phase
- Chromosomes become gradually visible under light microscope.
- Centrioles start moving towards opposite ends or poles and each centriole develops astral rays.
- Each chromosome is attached to the nuclear envelope through the attachment plate at both of its ends.
Homologous Chromosomes:
There are two sets of chromosomes in a diploid cell which undergo meiosis. One set of chromosomes is contributed by the male parent i and the other by the female parent. There are always two similar chromosomes having the same size, shape and position of centromere. In some organisms, the chromosomes give beaded appearance due to the presence of chromomeres (swollen area).
(ii) Zygotene (Yoked thread)
This is the next substage that takes place after the completion of the previous one. This is also a short lived stage like leptotene.
Following changes are seen during this phase
- Homologous chromosomes pair up. This pairing is done in such a way that the genes of the same character present on the two chromosomes lie exactly opposite to each other. This process of association is known as synapsis.
- It is revealed from the electron micrographic studies that the formation of synaptonemal complex takes place by a pair of homologous chromosomes that show synapsis. The complex so formed, on account of synapsis forms a bivalent or a tetrad.
(iii) Pachytene (Thick thread)
This is the stage which immediately follows zygotene where the pair of chromosomes become twisted spirally around each other and cannot be distinguished separately. This stage is comparatively long lived as compared to the previous two stages.
Following changes are seen during this stage
- Bivalent chromosomes are clearly seen as tetrads.
- In this stage, sometimes exchange of genes or crossing over between the two non-sister chromatids of homologous chromosomes occurs at the points called recombination nodules, which appear at intervals, on synaptonemal complex. By the end of pachytene recombination gets completed leaving the chromosomes linked at the sites of crossing over.
In this process, exchange of genetic material takes place between the non-sister chromatids of two homologpus chromosomes. It finally leads to recombination of genetic material on the two chromosomes.
(iv) Diplotene (Doube thread)
It is the stage of longest duration of all.
Following changes are observed during this stage
- In this, the synaptonemal complex appears to get dissolved while, the chromatids of each tetrad remain clearly visible.
- Recombined homologous chromosomes of the bivalents get separated and form chiasmata (X-shaped structures).
- Chiasmata formation is necessary for the separation of homologous chromosome which have undergone the process of crossing over.
(v) Diakinesis (Double ending)
This is the final stage of meiotic prophase-I. Also known as terminalisation, due to the shifting of chiasmata towards the end of the chromosomes.
Following changes are observed during this stage
- Chromosomes become fully condensed.
- Nucleolus degenerates.
- Breakdown of nuclear envelope into vesicles occurs.
- Formation of meiotic spindle (as in mitosis) in order to prepare the homologous chromosomes for separation also occurs.
- Diakinesis phase represents the transition from prophase to metaphase of meiosis-I.
Question 16.
Give an account of different phases a somatic cell undergoes during division process.
Answer:
Mitosis (M Phase):
In this type of division, the chromosomes replicate themselves and get equally distributed into daughter nuclei, i.e., the chromosome number in the parental and progeny cell (diploid) becomes the same. Therefore, it is also known as equational division.
Mitosis is also known as somatic cell division because it always occurs in somatic cells. Mitotic cell division is seen in the diploid somatic cells in animals, whereas, in plants, mitotic division is seen in both haploid and diploid cells.
It is known to be the phase of actual cell division, which starts with the division of nucleus, followed by the separation of daughter chromosomes, i.e., karyokinesis and terminates with the cytoplasmic division, i. e., cytokinesis.
Karyokinesis:
It is further divided into four main substages, i.e., prophase, metaphase, anaphase and telophase.
1. Prophase:
This phase is known for the initiation of condensation of chromosomal material, which during the process of chromatin condensation becomes untangled, and finally the centriole (already duplicated during S-phase of interphase) begins to move towards the opposite poles of the animal cell.
For the suitability in study we can categorise prophase as
(i) Early Prophase
During this phase, condensation of chromosomal material takes place in order to form compact mitotic chromosomes that are composed of two chromatids which are attached together at centromere.
The most conspicuous change that takes place during prophase is the formation of mitotic spindle. The initiation of mitotic spindle assembly, the micro-tubules and the proteinaceous components of the cell cytoplasm helps in the completion of the process. The mitotic spindle is formed between the two pairs of centrioles that migrate towards the opposite poles of the cell.
(ii) Late Prophase
At the end of the prophase, i.e., during late prophase the nucleolus disintegrates gradually and the nuclear envelope disappears. This disappearance marks the end of the prophase.
Question 17.
What is the significance of mitosis? Give details of the phases in between two successive M-phases.
Answer:
Mitosis (M Phase):
In this type of division, the chromosomes replicate themselves and get equally distributed into daughter nuclei, i.e., the chromosome number in the parental and progeny cell (diploid) becomes the same. Therefore, it is also known as equational division.
Mitosis is also known as somatic cell division because it always occurs in somatic cells. Mitotic cell division is seen in the diploid somatic cells in animals, whereas, in plants, mitotic division is seen in both haploid and diploid cells.
It is known to be the phase of actual cell division, which starts with the division of nucleus, followed by the separation of daughter chromosomes, i.e., karyokinesis and terminates with the cytoplasmic division, i. e., cytokinesis.
Question 18.
Give major points of comparision between mitosis, and meosis.
Answer:
Differences between Mitosis and Meiosis
| Mitosis | Meiosis |
| This division occurs in somatic cells. | It occurs in reproductive cells. |
| It is a single division. | It is a double division. |
| The daughter cells resemble each other as well as their mother cell. | The daughter cells neither resemble one another nor their mother cell. |
| Replication of chromosomes occurs before every mitotic division. | Replication of chromosomes occurs only once though meiosis is a double division. |
| Mitosis does not introduce variations. | Meiosis introduces variations. |
| Mitosis is required for growth, repair and healing. | Meiosis is involved in sexual reproduction. |