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NCERT Solutions Class 11 Biology Chapter 10 - Cell Cycle and Cell Division
NCERT Solutions for Class 11 Biology Chapter 10, Cell Cycle and Cell Division, explain how cells grow, prepare for division, and produce new cells. The chapter covers important topics such as the cell cycle, DNA replication, mitosis, meiosis, karyokinesis, and cytokinesis. Students can understand the different stages of cell division and learn how chromosomes are organised and separated during these processes.
NCERT Solutions for Class 11 Biology Chapter 10 by ALLEN provide clear explanations of the stages of mitosis and meiosis, including the five stages of Prophase I: leptotene, zygotene, pachytene, diplotene, and diakinesis. Students can also understand the reduction in chromosome number during meiosis, the role of crossing over, and the differences between mitosis and meiosis. The solutions follow the concepts covered in NCERT Class 11 Biology Chapter 10 and help students prepare for questions based on cell cycle and cell division.
1.0NCERT Solutions for Class 11 Biology Chapter 10 Cell Cycle and Cell Division: Key Concepts
Class 11 Biology Chapter 10, Cell Cycle and Cell Division, explains the stages through which a cell grows, duplicates its genetic material, and divides to form new cells. The key concepts covered in this chapter include:
- Cell Cycle: Understand the different stages of the cell cycle, including G1, S, G2, and M phases, and the major events that occur during each stage.
- Mitosis: Study the stages of nuclear division, including prophase, metaphase, anaphase, and telophase, and understand the changes that occur in chromosomes during each stage.
- Cytokinesis: Learn how the cytoplasm divides after nuclear division and understand the difference between cell plate formation in plant cells and cleavage furrow formation in animal cells.
- Significance of Mitosis: Understand the role of mitosis in growth, development, cell replacement, and repair, while maintaining the chromosome number.
- Meiosis: Study the specialised type of cell division that reduces the chromosome number by half and produces haploid cells.
- Meiosis I: Understand the stages of Meiosis I, with special focus on Prophase I, which includes leptotene, zygotene, pachytene, diplotene, and diakinesis.
- Meiosis II: Learn about the stages of Meiosis II and how they lead to the formation of four haploid daughter cells.
- Crossing Over and Genetic Variation: Understand the role of crossing over during pachytene of Prophase I in producing genetic variation.
- Significance of Meiosis: Learn how meiosis helps maintain the chromosome number across generations and contributes to genetic variation.
2.0NCERT Solutions Class 11 Biology Chapter 10 -Cell Cycle and Cell Division: Detailed Solutions
- What is the average cell cycle span for a mammalian cell?
Ans. 24 hours.
- Distinguish cytokinesis from karyokinesis.
Ans. Differences between cytokinesis and karyokinesis are:
- Describe the events taking place during the interphase.
Ans. The interphase, though called the resting phase, is the time during which the cell is preparing for division by undergoing both cell growth and DNA replication in an orderly manner. The interphase is further divided into three phases:
- (Gap 1) phase
- S (Synthesis) phase
- (Gap 2) phase
phase corresponds to the interval between mitosis and initiation of DNA replication. During 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 begins in the nucleus, and the centriole duplicates in the cytoplasm.
During the phase synthesis of DNA stops while cell growth continues with synthesis of protein and RNA in preparation for mitosis.
- What is (quiescent phase) of cell cycle?
Ans. 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 unless called on to do so depending on the requirement of the organism.
- Why is mitosis called equational division?
Ans. The number of chromosomes in the parent and progeny cells is the same, so mitosis is called as equational division.
- 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 chromosomes takes place. (iv) Crossing over between homologous chromosomes takes place.
Ans.
(i) Metaphase (ii) Anaphase (iii) Zygotene of prophase I of meiosis 1 (iv) Pachytene of prophase I of meiosis I
- Describe the following: (a) Synapsis (b) Bivalent (c) Chiasmata Draw a diagram to illustrate your answer.
Ans.
(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 X-shaped structures are called chiasmata.
- How does cytokinesis in plant cells differ from that in animal cells? Ans. Plant cytokinesis and animal cytokinesis differ in following respects:
- Find examples where the four daughter cells from meiosis are equal in size and where they are found unequal in size. Ans. 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 daughter cells are unequal in size.
- Distinguish anaphase of mitosis from anaphase I of meiosis. Ans. Anaphase of mitosis : 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.
- List the main differences between mitosis and meiosis.
Ans.
12. What is the significance of meiosis?
Ans. Meiosis is the mechanism by which conservation of specific chromosome number of each species is achieved across generations in sexually reproducing organisms, even though the process, per se, paradoxically, results in reduction of chromosome number by half. It also increases the genetic variability in the population of organisms from one generation to the next. Variations are very important for the process of evolution.
- 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.
Ans.
(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.
- Can there be mitosis without DNA replication in S-phase? Ans. No there cannot be any mitotic division without-DNA replication in 'S' phase.
- Can there be DNA replication without cell division? Sol. Yes. polyploidy is the multiplication of chromosomes present in a set in nucleus without karyokinesis and cytokinesis result-ing in numerous copies of set within cell. This increase in sets of chromosomes is called polyploidy.
- Analyse the events during every stage of cell cycle and notice how the following two parameters change. (i) number of chromosomes (N) per cell-B (ii) amount of DNA content (C) per cell-B Ans. 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 , 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.
3.0NCERT Class 11 Biology – Chapter-Wise Solutions & Explanations
Get NCERT Solutions for Class 11 Biology for every chapter and solved answers for all questions in the textbook. Understand key concepts, revise important topics, and improve your Biology preparation for exams.
4.0Key Features of NCERT Solutions for Class 11 Biology Chapter 10
- DNA Content and Chromosome Number: Clear explanations of changes in DNA content and chromosome number during the S phase, mitosis, and meiosis to help students understand ploidy and DNA content.
- Prophase I: Describes the five stages of Prophase I in detail, with emphasis on key events like as synapsis in zygotene and crossing-over in pachytene.
- Mitosis vs. Meiosis: Clear comparison of mitosis and meiosis based on their stages, number of daughter cells, chromosome number, and genetic outcome.
- Cytokinesis: Step-by-step explanation of cell plate formation in plant cells and cleavage furrow formation in animal cells during cytokinesis.
- Phase Identification: Diagram-based explanations to help students identify different stages of cell division by observing chromosome arrangement and movement, such as the metaphase plate.
- Complete NCERT Exercise Coverage: Answers to all NCERT exercise questions with clear explanations based on the concepts covered in Class 11 Biology Chapter 10.
- Prepared by Expert Faculty: Prepared by ALLEN subject experts with explanations aligned with the concepts given in NCERT Class 11 Biology Chapter 10.