NCERT exemplar Class 11 Biology solutions chapter 10 talk about one very important process that takes place in the bodies of living organisms and is considered crucial for their growth and development. The life of every living organism first starts with a single cell as we know, then new cells come into existence from pre-existing cells. The process of how the cells multiply their genome and eventually divide into two daughter cells is called the cell cycle. This NCERT exemplar Class 11 Biology solutions chapter 10 includes information about the cell cycle, DNA, the different stages of the cell cycle, the process of mitosis and meiosis along with the significance of both and how they are different from each other.
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Here are the NCERT exemplar Class 11 Biology solutions of chapter 10 Cell Cycle and Cell Division:
Multiple Choice Questions:
Meiosis in diploid organisms results in
(a) Production of gametes
(b) Reduction in the number of chromosomes
(c) All of the above
(d) Introduction of variation
The answer is the option (c) All of the above
Explanation: Meiosis results in a reduction of the number of chromosomes and gametes are formed only after meiosis. Crossing over during meiosis leads to variations. Hence, all the options are correct.
At which stage of meiosis does the genetic constitution of gametes is finally decided
(a) Metaphase I
(b) Anaphase I
(c) Metaphase II
(d) Anaphase II
The answer is the option (b) Anaphase I
Explanation: In anaphase I of meiosis, the actual reduction occurs which decides the genetic constitution of the gamete. Every single homologous chromosome with its two chromatids and unsegregated centromere moves to the opposite poles of the cell.
Meiosis occurs in organisms during
(a) Sexual reproduction
(b) Vegetative reproduction
(c) Both sexual and vegetative reproduction
(d) None of the above
The answer is the option (c) Sexual reproduction
Explanation: Option ‘a’ is correct because there is no need for meiosis during vegetative reproduction.
During anaphase-I of meiosis
(a) Non-sister chromatids separate
(b) Non-homologous autosomes separate
(c) Sister chromatids separate
(d) Homologous chromosomes separate
(d) Homologous chromosomes separate
Explanation: Homologous chromosomes segregated during Anaphase I.
Mitosis is characterised by
(a) Reduction division
(b) Both reduction and equal division
(c) Equal division
(d) Pairing of homologous chromosomes
The answer is the option (c) Equal division
Explanation: There is no reduction in chromosomes, and hence mitosis is also called an equal division.
A bivalent of meiosis-I consists of
(a) Four chromatids and two centromere
(b) Two chromatids and two centromere
(c) Two chromatids and one centromere
(d) Four chromatids and four centromere
Ans. The answer is the option (a) Four chromatids and two centromere
Explanation: Bivalent is formed by pairing of two chromosomes. Hence, bivalent contains four chromatids and four centromeres.
Cells which are not dividing are likely to be at
(c) S phase
The answer is the option (d) G0
Explanation: Phase G0 is also called the quiescent phase, and no cell division takes place during this phase.
Which of the events listed below is not observed during mitosis?
(a) Crossing over
(b) Movement of centrioles to opposite poles
(c) Appearance of chromosomes with two chromatids joined together at the centromere.
(d) Chromatin condensation
The answer is the option (a) Crossing over
Explanation: Crossing overtakes place only during prophase I of meiosis.
Identify the wrong statement about meiosis
(a) Pairing of homologous chromosomes
(b) Two cycles of DNA replication occur
(c) At the end of meiosis, the number of chromosomes is reduced to half
(d) Four haploid cells are formed
The answer is the option (b) Two cycles of DNA replication occur
Explanation: The number of chromosomes in daughter cells gets half, so there is no need for another cycle of DNA replication.
Select the correct statement about G1 phase
(a) Cell is metabolically inactive
(b) It is not a phase of synthesis of macromolecules
(c) DNA in the cell does not replicate
(d) Cell stops growing
The answer is the option (c) DNA in the cell does not replicate
Explanation: The cell is metabolically active during the G1 phase and continues to grow and carries out the synthesis of macromolecules, but DNA synthesis does not take place in this phase.
Mitosis results in producing two cells which are similar to each other. What would be the consequence if each of the following irregularities occur during mitosis?
(a) Nuclear membrane fails to disintegrate
(b) Duplication of DNA does not occur
(c) Centromeres do not divide
(d) Cytokinesis does not occur.
(a) The spindle fibres would not be able to reach chromosomes if the nuclear membrane fails to disintegrate. Because of this, the chromosomes would not be able to reach the opposite poles of the cell.
(b) The cell may not be able to reach the M phase if the DNA duplication does not take place. This shall result in the cessation of the cell cycle.
(c) If the division of centromeres does not take place, then one of the daughter cells will get a complete pair of chromosomes, and another daughter cell will get none. This may result in trisomy.
(d) If cytokinesis does not occur, then a cell with the multinucleate condition would be formed.
How does cytokinesis in plant cells differ from that in animal cells?
It takes place through cleavage.
It takes place by the cell plate method.
Soon after anaphase, there is a degeneration of spindle.
During cytokinesis, the spindle persists.
The cleavage progresses centripetally.
The growth of the cell plate takes place centrifugally.
The derivation of the new cell membrane takes place through endoplasmic reticulum.
The derivation of the new cell membrane is from the vesicles of Golgi apparatus.
Long Answer Type Questions:
Comment on the statement - Telophase is reverse of prophase.
Following contrasting features between prophase and telophase prove that telophase is reverse of prophase.
Mitochondria, Golgi Complex, ER, etc. disappear in the prophase.
Nuclear membrane starts to fall apart during the prophase.
Chromosomes become clearly visible in the prophase.
Mitochondria, ER, Golgi Complex, etc. reappear in the telophase.
Nuclear membrane starts to integrate during the telophase.
Chromosomes start to lose their visibility in this telophase.
What are the various stages of meiotic prophase-I? Enumerate the chromosomal events during each stage?
These are the different stages of meiotic prophase:
(a) Leptotene: During the stage of leptotene, the chromosomes are slowly visible under a light microscope. The compression of chromosomes continues until the end of this stage. The sister chromatids which are tightly bound so that they cannot be differentiated from each other.
(b) Zygotene: Zygotene is the stage where the chromosomes start forming into pairs.This process of formation is called synapsis. Formation of synapsis goes along with the formation of synaptonemal complexes. Each pair formed in this process is called a bivalent or tetrad.
(c) Pachytene: In the stage of pachytene, the bivalent chromosomes get detached.Reconnection of the nodules starts to appear on the tetrads. The recombination nodule is the site at which the crossing over of the non-sister chromatid takes place. Crossing over happens between non-sister chromatids of the homologous chromosomes.Crossing over helps in the exchange of genes between two homologous chromosomes.
(d) Diplotene: In the stage of diplotene, the synaptonemal complex starts to break down. The reconnected chromosomes begin to segregate from each other. But they are connected at the site of crossing over. This makes an X-shaped structure called chiasmata.
(e) Diakinesis: In the Diakinesis stage, the Chiasmata is terminated. The nucleolus disappears in this process, and so does the nuclear membrane.
Differentiate between the events of mitosis and meiosis.
Prophase is shorter in duration. Chromosomes do not become segregated at this stage. Chromosomes show two distinct chromatids. No crossing over takes place during this stage. Prophase is simple and is not distinguishable into sub-stages.
Prophase–I is of longer duration, while prophase–II is of shorter duration. Chromosomes are quite distinct. Chromosomes of prophase–I do not show distinct chromatids. Chiasmata is formed, and crossing overtakes place.
A single metaphasic plate is formed during metaphase. Chromosomes are independent in this phase and do not show connections. Limbs of chromosomes are in different directions. Two chromatids of a chromosome are genetically similar.
Two metaphasic plates are formed during metaphase–I but a single metaphasic plate is formed during metaphase–II. The Homologous chromosomes are interconnected. Limbs of chromosomes point towards the center. The two chromatids of a chromosome are mostly genetically different.
Centromere splits along its length to form two centromeres during anaphase. Chromosomes are single stranded. Similar chromosomes move towards the opposite poles.
During anaphase–I, centromeres do not require segregation, but segregation of centromere takes place during anaphase–II. Double-stranded chromosomes are visible in anaphase–I, but during anaphase–II, single-stranded chromosomes are visible. Dissimilar chromosomes move towards the opposite poles.
Telophase is of longer duration. It produces the interphase nuclei.
Telophase is shorter in case of meiosis.
Cytokinesis is a process that happens after every mitosis. Two daughter cells are formed at the end of this process.
Cytokinesis does not happen after meiosis–I but it happens after the second stage of meiosis. Four daughter cells are formed at the end of meiosis 2.
Write a brief note on the following
(a) Synaptonemal complex
(b) Metaphase plate
(a) Synaptonemal complex consists of protein. It is made between two homologous chromosomes in the process of meiosis. It is the site of matching, synapsis and recombination. During prophase–I of meiosis, the homologous chromosomes get matched through the synaptonemal complex. Through this complex, the exchange of genes takes place. Hence, reconnection or recombination of genetic characters happens through a synaptonemal complex.
(b) The metaphase plate is an imaginary line which is at equal distances from the two centrosome poles. During the process of metaphase, the chromosomes get together at the metaphase plate. The even alignment of chromosomes happens because of the facing kinetochore microtubules.
Write briefly the significance of mitosis and meiosis in multicellular organisms.
Significance of Mitosis:
Mitosis facilitates the development of single-cell zygote into a full-grown organism. It helps growth of an organism. It helps repair worn out or damaged tissues. It helps vegetative propagation in flowering plants. It helps regeneration in some animals.
Significance of Meiosis:
Meiosis makes sure that the number of chromosomes becomes diploid in gametes. This aids in making sure that the conservation of particular chromosomal numbers in species. Meiosis helps genetic variability in populations. This happens due to crossing over during prophase–I.
NCERT Exemplar Class 11 Biology Solutions Chapter 10 - Main Subtopics
- Cell Cycle
- Phases of cell cycle
- M Phase
- Significance of Mitosis
- Meiosis I
- Meiosis II
- Significance of Meiosis
What will the students learn in NCERT Exemplar Class 11 Biology Solutions Chapter 10?
Class 11 Biology NCERT exemplar solutions chapter 10 will provide a deeper insight into the functioning of their body and why it works the way it does. It covers all the important topics from the process of meiosis and mitosis to the significance of DNA and how it is replicated. It answers the questions that the students might have after knowing a part of it and also provides suitable, relevant diagrams of the same.
It is important to understand cell theory and cell division to understand biology better as the cell is the basic functional unit of life. Finding and knowing about different organisms have been easy ever since the concept of cell theory was developed by Theodor Schwann in 1839.
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NCERT Exemplar Class 11 Biology Solutions Chapter 10 - Important Topics
Class 11 Biology NCERT exemplar solutions chapter 10 is important for both board exams and other competitive exams that a student might appear for. NCERT Exemplar Class 11 Biology solutions chapter 10 deals with the reason behind their growth and development of all living organisms.
Class 11 Biology NCERT exemplar solutions chapter 10 has detailed that Cell Cycle, phases of the cell cycle, M phases, mitosis, meiosis, and their significance are important topics which students should pay extra attention to.
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