Class 11 Biology Chapter 10 Cell Cycle and Cell Division Notes - FREE PDF Download
Cell cycle
The cell cycle is defined as the series of changes that a cell undergoes which results in the division of cells into two daughter cells and its growth. The cell cycle is divided into two phases- interphase and mitosis. The average duration of a cell completing its two phases in humans is 24 hours. Of this, the duration of mitosis is for only 1 hour. Therefore, the majority of time of a cell cycle is spent in interphase.
Interphase
It is a phase in which different changes occur to prepare the cell for cell division. It is further divided into the following phases
The G1 phase also called the first gap phase deals with the biosynthetic activities which occur at a very fast rate. Cell synthesizes more proteins, increasing the number of mitochondria and ribosomes. The cell also prepares itself for DNA replication.
In the S phase, DNA is replicated. At the end of DNA replication, each chromosome will have two sister chromatids. So the content of DNA gets doubled, but ploidy remains the same.
G2 phase, where the cell prepares itself for mitosis involves protein synthesis and leads to further growth of the cell.
Mitosis
Called equational division as the number of chromosomes in the daughter cell and the parent cell remains the same. It begins with nuclear division. This is known as karyokinesis. Chromosomes get distributed equally during mitosis. Only somatic cells undergo mitosis.
It is divided into the following phases
Prophase
In prophase, chromatin condenses to form chromosomes. Two identical copies of each chromosome are attached to the centromere. During the end of this phase, the nucleolus dissolves. The nuclear membrane also disintegrates at the end. The centrosome moves to the opposite poles. Spindle fibers start to appear.
Metaphase
Here chromosomes get aligned on the equatorial plate. It is also called metaplate. The method of analyzing the metaphase chromosomes helps in cytogenetics and cancer studies.
Anaphase
It is the shortest stage of the cell cycle. During this phase, the replicated chromosomes move apart and daughter chromatids move to the opposite poles. Chromosomes get condensed during the late anaphase. The chromosomes become Y-shaped while moving towards the poles on opposite sites.
Telophase
The end result of telophase is the formation of two daughter nuclei. Nucleolus and nuclear membrane reappear. The late telophase is marked by cytokinesis. This is the last phase of mitosis. Finally, the chromosomes reach the poles.
Cytokinesis
The division of the cytoplasm, its organelles, and membrane to form two cells is known as cytokinesis. It results in the division of a cell into two daughter cells that are identical to its parent.
Importance of Mitosis
Produce genetically identical daughter cells.
Growth of the body takes place as a result of mitosis.
Cell repair and replacement also occur as a result of mitosis.
Maintenance of nucleo-cytoplasmic ratio.
Cell Cycle Exit
Some cells divide at a fast rate whereas some divide slowly and some even do not divide once they are formed. Those cells which do not divide once formed, enter into a phase known as GO phase. For example, neuronal cells once formed will not divide.
Meiosis
Meiosis is also called reductional division as it reduces the number of chromosomes in the progenies to half the parent cell. There are two types of meiosis; I and II which results in gametes such as sperm or egg.
Meiosis I
It is divided into the following phases
Prophase I
The longest phase of meiosis I is where homologous chromosome pairs and DNA segments are exchanged. This process is also known as recombination. It is further divided into following
Leptotene
First stage of meiosis is leptotene
Individual chromosomes subsist with two sister chromatids.
Elements of synaptonemal complex assemble.
Condensation and coiling of chromosomes takes place in leptotene
Zygotene
Chromosomes align together as homologous pairs
Synapses of homologous chromosomes occur.
The paired chromosomes are known as bivalent or tetrad due to its appearance
Pachytene
Crossing over and homologous recombination occurs during the pachytene stage
Chiasmata are X-shaped structures as a result where homologous chromosomes remain in contact.
Diplotene
Homologous chromosomes start to separate.
Synaptonemal complex disassemble.
Chromosomes remain attached to the chiasmata.
Diakinesis
Chromosomes condense further so that four parts of the tetrads are visible.
The nucleoli disappear, and the nuclear membrane disintegrates.
Mitotic spindle starts to form.
Metaphase I
Homologous chromosomes remain aligned on the meta plate.
The replicated chromosomes are collectively bound together with a protein known as cohesin.
Anaphase I
Homologous chromosomes are pulled to the opposite poles as the result of the shortening of microtubules. The cohesin (protein complex) degrades from the chromosome arms and remains safe around the centromere. Thus the sister chromatids exist together while the homologus segregate.
Telophase I
The daughter cell contains half the number of chromosomes as compared to the parent cell. The spindle begins to disappear which was formed of microtubules. Once again chromosomes from chromatin. Sister chromatids remain attached together.
Meiosis II
Meiosis II is the second meiotic division. Similar to mitosis in process, but the genetic results are different. Products formed are four haploid cells from the two haploid cells produced in meiosis I.
The four main steps of Meiosis II are:- Prophase II, Metaphase II, Anaphase II, and Telophase II.
In prophase II nucleoli and nuclear membrane disappear, shortening and thickening of the chromatids occur. Centrosomes move to the poles and spindle fibers are formed for the second meiotic division.
In metaphase II, the centromeres are present with two kinetochores attached to spindle fibers from the centrosomes at opposite poles. When compared to meiosis I, the metaplate is rotated perpendicular to the previous plate by 90 degrees.
Anaphase II is determined by sister chromatid segregation. The remaining protein cohesin degrades to allow segregation of sister chromatids.
Telophase II which is similar to telophase I, results in the de-condensation of chromosomes. Nuclear envelopes reorganize and cleavage. Cell plate formation produces four daughter cells, each with a haploid set of chromosomes.
Significance of Meiosis:
Maintenance of chromosome number generation after generation in case of sexual reproduction.
Increases variation in the population.
5 Important Topics of Biology Class 11 Chapter 10 You Shouldn’t Miss!
Importance of Cell Cycle and Cell Division Class 11 Short Notes
Cell Division Class 11 Notes PDF provides a strong understanding of the basic concept of cell cycle and cell division, which are essential for learning more complex biological processes in higher classes.
Cell cycle and Cell division a fundamental chapters for NEET and other competitive exams, making these notes crucial for exam preparation.
The notes break down complex concepts into simple, easy-to-understand points, helping students grasp the material quickly.
Well-organised Cell Cycle and Cell Division Short Notes allow for efficient revision, covering key points, important reactions, and frequently asked structures in exams.
Diagrams and examples included in the notes enhance understanding and retention of the subject matter.
Cell Division Class 11 Notes PDF covers all important topics and subtopics, ensuring that students have a complete understanding of the chapter.
Tips for Learning the Class 11 Biology Chapter 10 Cell Cycle and Cell Division
Familiarise yourself with key terms like interphase, mitosis, meiosis, cytokinesis, chromatin, chromosomes, and spindle fibres.
Review and draw diagrams of the cell cycle, phases of mitosis, and meiosis to help with memorization.
Learn the cell cycle and mitosis/meiosis phases step-by-step, focusing on what happens in each phase and its purpose.
Understand how cell division impacts growth, repair, and reproduction by relating concepts to real-life examples.
Solve end-of-chapter questions and previous year’s papers to test your understanding and application of concepts.
Periodically review the material to reinforce your memory and understanding.
Conclusion
The Cell Cycle and Cell Division are fundamental processes essential for life. They enable growth, repair, and reproduction by ensuring that cells divide correctly and pass on genetic information accurately. Understanding the phases of the cell cycle, including interphase and mitosis, as well as the process of meiosis, helps in grasping how organisms develop and maintain their functions. These processes are crucial for both single-celled and multicellular organisms. By regularly reviewing Cell Cycle and Cell Division Class 11 Notes and practising with diagrams and key points, you will strengthen your grasp of the material.
Related Study Materials for Class 11 Biology Chapter 10 Cell Cycle and Cell Division
Students can also download additional study materials provided by Vedantu for Biology Class 11, Chapter 10–
Revision Notes Links for Class 11 Biology
Important Study Materials for Class 11 Biology
FAQs on Cell Cycle and Cell Division Class 11 Notes: CBSE Biology Chapter 10
1. What are the main phases of the cell cycle according to Class 11 Biology revision notes?
The main phases of the cell cycle are interphase and mitotic phase. Interphase includes the G1 phase (cell growth and preparation), S phase (DNA replication), and G2 phase (final preparation for division). The mitotic phase involves both mitosis and cytokinesis, resulting in two daughter cells.
2. How does mitosis differ from meiosis in terms of process and outcome?
Mitosis is a single division producing two genetically identical diploid daughter cells from a somatic cell, maintaining chromosome number. Meiosis involves two consecutive divisions resulting in four genetically unique haploid cells (gametes), each with half the parent chromosome number, contributing to genetic variation.
3. Why is the interphase considered the most critical period for cell preparation during the cell cycle?
The interphase is crucial because the cell grows, performs regular functions, synthesizes proteins, replicates its DNA, and prepares necessary organelles. Most of the cell’s time is spent here, ensuring successful and error-free division.
4. Summarize the key steps of mitosis as described in Class 11 Biology Chapter 10 notes.
Mitosis includes:
- Prophase: Chromatin condenses; nucleus and nucleolus disappear; spindle fibres form.
- Metaphase: Chromosomes align at the cell’s equatorial plate.
- Anaphase: Sister chromatids separate and move toward opposite poles.
- Telophase: New nuclear membranes form, followed by cytokinesis resulting in two identical daughter cells.
5. What roles do cell division and the cell cycle play in growth and repair in organisms?
Cell division enables an organism to grow by producing new cells and replaces damaged or dead cells to maintain tissue health. The cell cycle controls the timing and sequence of these processes, ensuring genetic material is accurately passed to daughter cells.
6. How does the cell ensure genetic consistency during cell division?
The cell ensures genetic consistency by precisely replicating DNA during the S phase of interphase and by equally distributing chromosomes to daughter cells during mitosis. This maintains the correct chromosome number in each new cell.
7. Why is meiosis important in sexually reproducing organisms, as per revision notes?
Meiosis is essential for producing gametes (sperm and egg cells) that contain half the parent cell's chromosomes. This reductional division restores the species' chromosome number during fertilisation and increases genetic variation in the population.
8. What is the significance of the G0 phase in the cell cycle?
The G0 phase is a resting state where cells exit the active cell cycle, ceasing division. Cells like neurons remain in G0 permanently, allowing for specialization and preventing unnecessary cell proliferation.
9. How does crossing over during meiosis contribute to genetic diversity?
During Prophase I of meiosis, homologous chromosomes exchange segments in a process termed crossing over. This recombination shuffles genes, producing new allele combinations and contributing to genetic diversity in offspring.
10. What revision strategies are recommended for CBSE Class 11 Biology Chapter 10?
Effective revision strategies include:
- Understanding key terms such as interphase, mitosis, meiosis, and cytokinesis
- Drawing labelled diagrams of cell division stages
- Summarizing main concepts and creating concept maps
- Regular self-testing with previous questions for strong recall
11. How do errors in the cell cycle or cell division affect an organism?
Errors such as uncontrolled division or faulty chromosome separation can lead to conditions like cancer or genetic disorders. Proper regulation of the cell cycle ensures healthy growth and functioning.
12. What are the key differences in chromosome movement during mitosis and meiosis I?
In mitosis, sister chromatids separate and move to opposite poles. In meiosis I, homologous chromosomes separate while sister chromatids remain attached, reducing chromosome number by half in each cell.
