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Welcome to Swastik Classes! In this chapter, we delve into the intricate world of cell biology as we explore the “Cell Cycle and Cell Division.”
The cell cycle is a fundamental process that governs the growth, development, and reproduction of all living organisms. Understanding the mechanisms underlying cell division is crucial to comprehend the complexities of life itself.
In this comprehensive series of NCERT solutions for Class 11 Biology Chapter 10, we have meticulously crafted detailed explanations and step-by-step solutions to help you navigate through this intriguing subject with ease. Our team of experienced educators at Swastik Classes has taken great care to ensure that every concept is explained in a clear and concise manner, making it accessible to students of all levels of understanding.
We cover a wide range of topics in this chapter, including the phases of the cell cycle, mitosis, meiosis, and the significance of cell division in growth, repair, and reproduction. Our solutions provide not only the answers to the exercises in the NCERT textbook but also offer additional insights, tips, and illustrations to enhance your comprehension and retention of the material.
At Swastik Classes, we believe in fostering a love for learning and promoting a deep understanding of biology. Our NCERT solutions for Class 11 Biology Chapter 10 aim to empower you with the knowledge and skills necessary to excel in your examinations and beyond. So, whether you’re a curious learner seeking a better grasp of cell biology or a diligent student preparing for your exams, Swastik Classes is here to support you every step of the way.
Embark on this fascinating journey of cell cycle and cell division with us and unlock the secrets of life itself. Let’s dive in together and explore the intricacies of the microscopic world that shapes our existence.
NCERT Solutions for Class 11 Biology Chapter 10: Cell Cycle and Cell Division – Exercises
1. What is the average cell cycle span for a mammalian cell?
Sol. 24 hours.
2. Distinguish cytokinesis from karyokinesis.
Sol. Differences between cytokinesis and karyokinesis are:
3. Describe the events taking place during interphase.
Sol. The interphase, though called the resting phase, is metabolically quite active. It is the time during which the cell prepares itself for division by undergoing both cell growth and DNA replication in an orderly manner. The interphase is further divided into three phases:
• G1 (Gap 1) phase
• S (Synthesis) phase
• G2 (Gap 2) phase
G1 phase corresponds to the interval between mitosis of previous cell cycle and initiation of DNA replication. During G1 phase the cell is metabolically active and grows continuously but does not replicate its DNA S or synthesis phase marks the period during which DNA synthesis or replication takes place. During this time the amount of DNA doubles per cell. In animal cells, during the S phase, DNA replication occurs in the nucleus, and the centriole duplicates in the cytoplasm. During the G2 phase synthesis of DNA stops while cell growth continues with synthesis of protein and RNA in preparation for mitosis.
4. What is G0 (quiescent phase) of cell cycle?
Sol. G0 phase is the phase of inactivation of cell cycle due to non-availability of mitogens and energy rich compounds. Cells in this stage remain metabolically active but no longer proliferate i.e., do not grow or differentiate unless called on to do so depending on the requirement of the organism. E.g., Nerve and heart cells of chordates are in permanent G0 phase.
5. Why is mitosis called equational division?
Sol. Mitosis is a type of cell division in which chromosomes replicate and become equally distributed in two daughter nuclei so that the daughter cells come to have the same number and type of chromosomes as present in parent cell. So mitosis is called as equational division.
6. Name the stage of cell cycle at which each one of the following events occur:
(i) Chromosomes are moved to spindle equator.
(ii) Centromere splits and chromatids
separate.
(iii) Pairing between homologous chromo-somes takes place.
(iv) Crossing over between homologous chromosomes takes place.
Sol.
(i) Metaphase
(ii) Anaphase
(iii) Zygotene of prophase I of meiosis 1
(iv) Pachytene of prophase I of meiosis I
7. Describe the following:
(a) Synapsis
(b) Bivalent
(c) Chiasmata
Draw a diagram to illustrate your answer.
Sol. (a) Synapsis: During zygotene of prophase I stage homologou s chromosomes start pairing together and this process of association is called synapsis. Electron micrographs of this stage indicate that chromosome synapsis is accompanied by the formation of complex structure called synaptonemal complex.
(b) Bivalent: The complex formed by a pair of synapsed homologous chromosomes is called a bivalent or a tetrad i.e., 4 chromatids or a pair of chromosomes.
(c) Chiasmata: The beginning of diplotene is recognized by the dissolution of the synaptonemal complex and the tendency of the synapsed homologous chromosomes of the bivalents to separate from each other except at the sites of crossovers. These points of attachment (X-shaped structures) between the homologous chromosomes are called chiasmata.
8. How does cytokinesis in plant cells differ from that in animal cells?
Sol. Plant cytokinesis and animal cytokinesis differ in following respects:
9. Find examples where the four daughter cells from meiosis are equal in size and where they are found unequal in size.
Sol. During formation of male gametes (i.e., spermatozoa) in a typical mammal (i.e., human being), the four daughter cells formed from meiosis are equal in size. On the other hand, during formation of female gamete (i.e., ovum) in a typical mammal (i.e., human being), the four daughter cells are unequal in size.
10. Can there be DNA replication without cell division?
Sol. Yes. Endomitosis is the multiplication of chromosomes present in a set in nucleus without karyokinesis and cytokinesis result-ing in numerous copies within each cell. It is of 2 types.
Polyteny: Here chromosomes divide and redivide without separation of chromatids so that such chromosomes become multistranded with many copies of DNA. Such polytene (many stranded) chromosomes remain in permanent prophase stage and do not undergo cell cycle e.g., polytene (salivary glands) chromosome of Drosophila has 512- 1024 chromatids. Here number of sets of chromosomes does not change.
Polyploidy (endoduplication) : Here all chromosomes in a set divide and its chromatids separate but nucleus does not divide. This results in an increase in number of sets of chromosomes in the nucleus (4x, 8x….). This increase in sets of chromosomes is called polyploidy. It can be induced by colchicine and granosan. These chromosomes are normal and undergo cell cycle.
11. List the main differences between mitosis and meiosis.
Sol. 
12. Distinguish anaphase of mitosis from anaphase I of meiosis.
Sol. Anaphase of mitosis : It is the phase of shortest duration. APC (anaphase promoting complex) develops. It degenerates proteins -binding the two chromatids in the region of centromere. As a result, the centromere of each chromosome divides. This converts the two chromatids into daughter chromosomes each being attached to the spindle pole of its side by independent chromosomal fibre. The chromosomes move towards the spindle poles with the centromeres projecting towards the poles and the limbs trailing behind. There is corresponding shortening of chromosome fibres. The two pole-ward moving chromosomes of each type remain attached to each other by interzonal fibres. Ultimately, two groups of chromosomes come to lie at the spindle poles.
Anaphase I of meiosis : Chiasmata disappear completely and the homologous chromosomes separate. The process is called disjunction. The separated chromosomes (univalents) show divergent chromatids and are called dyads. They move towards the spindle poles and ultimately form two groups of haploid chromosomes.
13. What is the significance of meiosis?
Sol. The significance of meiosis is given below:
(i) Formation of gametes – Meiosis forms gametes that are essential for sexual reproduction.
(ii) Genetic information – It switches on the genetic information for the development of gametes or gametophytes and switches off the sporophytic information. ‘
(iii) Maintenance of chromosome number – Meiosis maintains the fixed number of chromosomes in sexually reproducing organisms by halving the same. It is essential since the chromosome number becomes double after fertilisation.
(iv) Assortment of chromosomes – In meiosis paternal and maternal chromosomes assort independently. It causes reshuffling of chromosomes and the traits controlled by them. The variations help the breeders in improving the races of useful plants and animals.
(v) Crossing over – It introduces new combination of traits or variations.
(vi) Mutations – Chromosomal and genomic mutations can take place by irregularities of meiotic divisions. Some of these mutations are useful to the organism and are perpetuated by natural selection.
(vii) Evidence of basic relationship of organisms – Details of meiosis are essentially similar in the majority of organisms showing their basic similarity and relationship.
14. Discuss with your teacher about
(i) haploid insects and lower plants where cell division occurs, and
(ii)some haploid cells in higher plants where cell division does not occur.
Sol. (i) Cell division occurs in haploid insect, such as drones of honey bee and lower plant like gametophyte of algae, bryophytes, and pteridophytes.
(ii) Synergids and antipodals in embryo sac of ovule are haploid cells where cell division does not occur.
15. Can there be mitosis without DNA replication in ’S’ phase?
Sol. No there cannot be any mitotic division without-DNA replication in ‘S’ phase.
16. Analyse the events during every stage of ceil cycle and notice how the following two parameters change.
(i) number of chromosomes (N) per cell
(ii) amount of DNA content (C) per cell
Sol. Number of chromosomes and amount of DNA change during S-phase and anaphase of cell cycle. 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.
In mitotic anaphase, number of chromosomes remains the same. It is only sister chromatids which move towards their respective poles. DNA content remains unchanged. In anaphase I of meiosis, number of chromosomes are reduced to half, i.e., from 2N to IN and also DNA content decrease to one half i.e., from 4C to 2C. In anaphase II of meiosis II DNA content decreases to one half from 2C to 1C but chromosome number remain same.
Conclusions for NCERT Solutions for Class 11 Biology Chapter 10: Cell Cycle and Cell Division
Swastik Classes is proud to present our NCERT Solutions for Class 11 Biology Chapter 10: Cell Cycle and Cell Division. We have provided comprehensive and reliable solutions that will assist you in understanding the intricate processes of cell division.
Through our detailed explanations and step-by-step solutions, we have strived to simplify complex concepts, making them accessible and engaging for students of all levels. Our experienced educators have carefully crafted the solutions to ensure clarity and accuracy, enabling you to grasp the fundamental principles of the cell cycle and cell division.
By studying this chapter, you have gained a deep understanding of the phases of the cell cycle, the mechanisms of mitosis and meiosis, and the significance of cell division in growth, repair, and reproduction. This knowledge forms the foundation for further exploration in the field of biology and serves as a stepping stone for your academic journey.
We at Swastik Classes believe in fostering a love for learning and providing the tools necessary for your success. Our NCERT Solutions not only offer answers to the textbook exercises but also provide additional insights and illustrations, helping you develop a strong conceptual understanding.
We hope that our NCERT Solutions have been valuable resources for you, aiding in your preparation for examinations and enhancing your overall understanding of the subject. Remember, the world of biology is vast and ever-evolving, and we encourage you to continue exploring and expanding your knowledge.
Thank you for choosing Swastik Classes as your learning partner. We wish you all the best in your academic endeavors and beyond.
- What is the cell cycle, and what are its phases?
- The cell cycle is a series of events that a cell goes through as it grows and divides. It consists of interphase and mitotic phase. Interphase is further divided into three phases: G1 (Gap 1), S (Synthesis), and G2 (Gap 2). The mitotic phase includes mitosis and cytokinesis.
- What is the significance of mitosis?
- Mitosis is the process of cell division that results in the formation of two identical daughter cells. It plays a crucial role in growth, repair, and asexual reproduction in organisms. Mitosis ensures that the genetic material is accurately distributed to each daughter cell, maintaining the genetic stability of the organism.
- How does meiosis differ from mitosis?
- Meiosis is a specialized form of cell division that occurs in reproductive cells (gametes) and leads to the formation of haploid cells. Unlike mitosis, meiosis involves two rounds of division (meiosis I and meiosis II), resulting in the production of four genetically unique daughter cells. Meiosis is vital for sexual reproduction and contributes to genetic variation.
- What are the major differences between plant and animal cell division?
- Plant and animal cells differ in their methods of cell division. Animal cells undergo cytokinesis by the formation of a cleavage furrow, which pinches the cell into two daughter cells. In contrast, plant cells form a cell plate during cytokinesis, which eventually develops into a cell wall that separates the daughter cells.
- Why is the cell cycle tightly regulated?
- The cell cycle is precisely regulated to ensure accurate replication and distribution of genetic material, as well as the proper growth and development of organisms. Regulatory mechanisms, such as checkpoints and cell cycle control proteins, monitor the integrity of DNA and ensure that cell division occurs only when all requirements are met. This regulation helps prevent the formation of abnormal cells and maintains the overall health and functioning of the organism.
