NCERT Class 11 Biology Chapter 10 Notes Cell Cycle And Cell Division- Download PDF

NCERT Class 11 Biology Chapter 10 Notes: Cell Cycle and Cell Division delves into the different events that take place within a cell's life. The Chapter notes give the summary of the main points, such as the cell cycle, its stages, mitosis, meiosis, cytokinesis, and karyokinesis. These notes make it easy for students to understand intricate points by presenting them in a simpler way.

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This Story also Contains

1. What is the Cell Cycle?
2. Phases of Cell Cycle
3. Regulation of the Cell Cycle
4. Important Topics of Class 11 Biology Chapter 10: Cell Cycle and Cell Division
5. Most Important Questions of Class 11 Biology Chapter 10
6. Approach to solve questions of Class 11 Biology Chapter 10 Cell Cycle and Cell Division
7. Chapter-Wise NCERT Class 11 Notes Biology

Having properly organized revision notes and NCERT solutions Chapter 10 proves to be quite useful, serving to save the student time in the process of exam preparation. Furthermore, one can download PDF of the NCERT Class 11 Biology Notes using the provided link, permitting offline access. The notes even include important NCERT textbook topic points that are useful for competitive exams.

The Cell Cycle and Cell Division NCERT Notes for Class 11 are a ready reference while preparing for the CBSE board exams, making revision easy. Students can improve their concepts by reading these well-organized notes in simple and easy language. For effective last-minute revision, download the CBSE Notes for Class 11 Biology Chapter 10 PDF and learn anywhere, anytime.

Also, students can refer to:

• NCERT Solutions for Class 11 Biology Chapter 10 Cell Cycle and Cell Division
• NCERT Exemplar Class 11 Biology Chapter 10 Solutions Cell Cycle and Cell Division

What is the Cell Cycle?

The cell cycle refers to the chain of linear events that the cell goes through during its lifespan, from initiation to division into two daughter cells. It is a vital process in the growth, development, repair, and reproduction of all organisms. The cell cycle helps genetic material be accurately duplicated and transferred to ensure there is genetic stability. Accurate control of the cell cycle is necessary to avoid a process of unchecked cell growth that may result in conditions such as cancer.

Phases of Cell Cycle

The cell cycle is broadly divided into two major phases:

1. Interphase (Preparation Phase)
   Interphase is the longest phase of the cell cycle, where the cell grows, replicates its DNA, and prepares for division. It is further divided into three sub-phases:

G₁ Phase (First Gap Phase):

• The cell grows in size and synthesizes proteins and organelles.

• It prepares for DNA replication.

• The G₁ checkpoint ensures conditions are favorable for DNA synthesis.

S Phase (Synthesis Phase):

• DNA replication occurs, doubling the genetic material.

• Each chromosome duplicates to form two identical sister chromatids.

• The number of chromosomes remains the same, but the amount of DNA doubles.

G₂ Phase (Second Gap Phase):

• The cell continues to grow and prepares for mitosis.

• Proteins required for cell division are synthesized.

• The G₂ checkpoint ensures DNA replication is error-free before proceeding to mitosis.

2. M Phase (Mitotic Phase – Cell Division Phase)
The M phase is the division phase, where the duplicated genetic material is evenly distributed into two daughter cells. It consists of:

• Karyokinesis (Nuclear Division) – Includes mitosis (for somatic cells) or meiosis (for gametes).

• Cytokinesis (Cytoplasmic Division) – Division of the cytoplasm to form two separate daughter cells.

Duration and Regulation of the Cell Cycle

The length of the cell cycle is different for different organisms and cell types. For instance, human cells will take approximately 24 hours to complete one cycle.

• The cell cycle is regulated by checkpoints that ensure no errors are made while dividing.
• Important regulators are cyclins and cyclin-dependent kinases (CDKs), which regulate the proper course of the cycle.
• If there is damage or error in DNA, the cell cycle can be stopped or corrected. If damage is not reversible, the cell is destroyed by apoptosis (programmed cell death) to avoid malfunctioning cells from dividing.

Regulation of the cell cycle is important in order to maintain normal growth and avoid diseases such as cancer, which is caused by unchecked cell division due to the failure of checkpoints.

Also Read:

• NCERT Books for Class 11
• NCERT Syllabus for Class 11

Mitosis: The Process of Somatic Cell Division

Mitosis is a form of cell division in which one parent cell divides to give rise to two genetically equivalent daughter cells, each having the same number of chromosomes as the parent cell. It takes place in somatic (body) cells and plays a critical role in growth, repair, and asexual reproduction.

Significance of Mitosis

• Retains the number of chromosomes (diploid to diploid).
• Preserves genetic stability by forming the same cells.
• Assists in tissue development and repair by replacing old or broken cells.
• Is very important in asexual reproduction in unicellular organisms such as Amoeba.

Stages of Mitosis

Mitosis consists of four primary stages:

1. Prophase (Initiation of Cell Division)

• Chromatin condenses into observable chromosomes, each made up of two sister chromatids united by a centromere.
• The nucleolus and nuclear membrane dissolve.
• Centrosomes migrate towards opposite poles, and the mitotic spindle (formed of microtubules) forms.

2. Metaphase (Chromosome Alignment)

• Chromosomes align on the equatorial plane (metaphase plate).
• Spindle fibers bind to the chromosomes' centromeres.
• This step is significant to ensure proper chromosome separation.

3. Anaphase (Chromatid Separation)

• Sister chromatids move apart as spindle fibers draw them toward opposite poles.
• After separation, each chromatid is a daughter chromosome.
• This guarantees each daughter cell has an equal number of chromosomes.

4. Telophase (Mitosis End)

• Chromosomes decondense into chromatin.
• The nucleolus and nuclear membrane reappear to form two distinct nuclei.
• The spindle fibers break down.

Cytokinesis: Final Step of Cell Division

After mitosis, the cytoplasm divides in a process called cytokinesis, forming two identical daughter cells.

• In animal cells, a cleavage furrow forms and pinches the cell into two.

• In plant cells, a cell plate forms, developing into a new cell wall.

Role of Mitosis in Growth, Repair, and Asexual Reproduction

• Mitosis increases the number of cells, helping in the growth of an organism from a single fertilized egg to a multicellular body.

• Essential for embryonic development and organ formation.

• Damaged or dead cells are replaced through mitosis (e.g., skin, blood, and liver cells).

• Helps in wound healing and tissue regeneration (e.g., starfish regrowing limbs).

• In unicellular organisms like bacteria, yeast, and Amoeba, mitosis enables asexual reproduction (binary fission or budding).

• Allows plants to propagate through vegetative reproduction (e.g., potato tubers, strawberry runners).

Meiosis

Meiosis is a reproductive cell division that takes place in germ cells (sperm and egg cells) by halving the number of chromosomes. It produces a haploid (n) gamete from a diploid (2n) parent cell. This way, when a fertilization process happens, the zygote resulting from it re-establishes a diploid number, thus ensuring stability in species' chromosomes.

Meiosis consists of two successive divisions:

Meiosis I (Reductional Division)

The stages of meiosis I includes

Prophase I:

• Chromatin condenses into chromosomes.

• Homologous chromosomes pair up (synapsis) to form tetrads.

• Crossing over (genetic exchange) occurs at chiasmata, ensuring variation.

• Nuclear membrane dissolves, and spindle fibers form.

Metaphase I:

• Homologous chromosome pairs align at the metaphase plate.

• Independent assortment of homologous chromosomes occurs, increasing variation.

Anaphase I:

• Homologous chromosomes separate and move to opposite poles, but sister chromatids remain together.

Telophase I and Cytokinesis:

• Chromosomes decondense, and two haploid daughter cells are formed.

Meiosis II (Equational Division)

The stages of meiosis II include:

Prophase II:

• Chromosomes condense again. Spindle fibers reappear.

Metaphase II:

• Chromosomes align at the metaphase plate, similar to mitosis.

Anaphase II:

• Sister chromatids separate and move to opposite poles.

Telophase II and Cytokinesis:

• Nuclear membranes reform, and four genetically unique haploid cells are produced.

How Meiosis Provides Genetic Variation

Meiosis adds genetic diversity by:

Crossing Over (Prophase I): Homologous chromosomes swap genetic information, forming new combinations of alleles.

Independent Assortment (Metaphase I): Random allocation of pairs of homologous chromosomes results in various genetic combinations.

Significance of Cell Cycle and Cell Division

Growth, Development, and Tissue Repair

• Mitosis facilitates organism growth by adding to the number of cells.
• Critical for embryonic development and organogenesis.
• Replaces dead or damaged cells, contributing to wound healing and tissue regeneration.

Function in Preserving Chromosome Number in Organisms

• Mitosis maintains daughter cells receiving the same genetic material, retaining the chromosome number.
• Meiosis halves the chromosome number in gametes, avoiding doubling in every generation and species stability.

Genetic Stability and Variations

• Mitosis ensures genetic stability by resulting in identical cells.
• Meiosis enhances genetic variety, which is essential for evolution and adaptation.

Differences Between Mitosis and Meiosis

Regulation of the Cell Cycle

Role of Cell Cycle Checkpoints

Cell cycle checkpoints are responsible for ensuring proper replication and division of DNA, and avoiding errors. Primary checkpoints are:

• G₁ Checkpoint: Ensures appropriate growth and conditions prior to DNA replication.
• G₂ Checkpoint: Verifies DNA damage prior to mitosis.
• M Checkpoint (Spindle Checkpoint): Verifies proper alignment of chromosomes prior to division.

Role of Cyclins and CDKs in Cell Cycle Control

• Cyclins are proteins that control the cycle by activating cyclin-dependent kinases (CDKs).
• CDKs initiate important events such as mitosis and DNA replication.
• There are various cyclins that operate during particular phases of the cell cycle to prevent chaotic movement.

Mutations in Control as a Cancer Cause

• Without proper checkpoints, cells continue dividing, causing cancerous growth.
• Mutations affecting tumor suppressors (e.g., p53) or proto-oncogenes (e.g., RAS) interrupt the regulation of the cell cycle.
• Mitosis that is unchecked mitosis causes tumors to develop and also metastasize.

Subject-Wise NCERT Exemplar Solutions

• NCERT Exemplar Class 11 Solutions
• NCERT Exemplar Class 11 Maths
• NCERT Exemplar Class 11 Physics
• NCERT Exemplar Class 11 Chemistry
• NCERT Exemplar Class 11 Biology

Important Topics of Class 11 Biology Chapter 10: Cell Cycle and Cell Division

The essential points from this chapter are listed below for quick and easy revision.

• Phases of the Cell Cycle

• Mitosis and Its Stages

• Meiosis and Its Significance

• Regulation of the Cell Cycle

Most Important Questions of Class 11 Biology Chapter 10

Some of the most important questions from this chapter are listed below to help in better preparation and understanding.

Question 1: The following are the stages of cell division:
A. Gap 2 phase
B. Cytokinesis
C. Synthesis phase
D. Karyokinesis
E. Gap 1 phase
Choose the correct sequence of stages from the options given below:

1. C-E-D-A-B

2. E-B-D-A-C

3. B-D-E-A-C

4. E-C-A-D-B

Answer:

The correct sequence of stages of cell division is

Gap 1 phase → Synthesis Phase → Gap 2 phase → Karyokinesis → Cytokinesis

Hence, the correct answer is option 4, E-C-A-D-B.

Question 2: A student observes a cell at the telophase stage in a plant sample brought from the field. He notices that, unlike normal telophase cells, there is no formation of a cell plate, and the cell contains more chromosomes than usual. What could be the reason behind this observation?

Answer:

Polyploid cells have a chromosome number that is more than double the haploid number, example Triticum aestivum (wheat) is a hexaploid (6n). Polyploid cells possess a chromosome count that exceeds double the haploid number.

Question 3: What is the purpose of meiosis in cell division?

Answer:

The purpose of meiosis in cellular division is to diminish the chromosome count by a factor of two, thereby producing gametes such as sperm and eggs in animals, or pollen and ovules in plants. This process guarantees that upon fertilization, where two gametes unite, the ensuing progeny will possess the precise number of chromosomes.

Question 4: What will the cell do if the cell cycle is halted at the G₂ checkpoint?

Answer:

The G2 checkpoint verifies that DNA replication was completed and that the cell is prepared to proceed to the mitotic phase of the cell cycle. The cell will halt at the G2 checkpoint and activate DNA repair mechanisms to fix any damaged DNA before continuing if any is present.

Question 5: What occurs if cell cycle regulation is ineffective?

Answer:

Ineffective cell cycle regulation can cause cells to proliferate out of control, which can result in the growth of cancer. Cell growth and division can occur unchecked if there are any flaws or irregularities in the processes that control the cell cycle, which is a highly regulated process. Failure of the checkpoint mechanisms may allow the accumulation of mutations necessary for the ultimate onset of cancer by preventing the repair of damaged DNA.

Subject-Wise NCERT Solutions

• NCERT Solutions for Class 11 Mathematics
• NCERT Solutions for Class 11 Chemistry
• NCERT Solutions for Class 11 Physics

• NCERT Solutions for Class 11 Biology

Approach to solve questions of Class 11 Biology Chapter 10 Cell Cycle and Cell Division

Students should first try to understand all stages of the cell cycle, including interphase (G₁, S, G₂ phases) and M phase (mitosis and meiosis). They should focus on important topics like the significance of the cell cycle, differences between mitosis and meiosis, and the regulation of the cell cycle. Some key terminologies, such as cytokinesis, chromosomal behavior, spindle formation, and synapsis, need to be read repeatedly to get a clear vision. Students should practice the labeled diagrams of mitosis and meiosis, and the entire process can be more easily understood by creating flow charts. Solving previous years' questions will help in quick revision and to grasp the concepts clearly.

Chapter-Wise NCERT Class 11 Notes Biology

Below are all the chapter-wise links presented in a simple and easy-to-understand table format to help with quick revision and learning.