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

The NCERT Chapter 10 Cycle and Cell Division discusses all the events that occur during the life of the cell. The NCERT Class 11 Biology chapter 10 notes cover a brief outline of the chapter cell cycle and cell division. The main topics covered in NCERT Class 11 Biology Notes are cell cycle, phases of cell cycle, mitosis, meiosis, cytokinesis, karyokinesis, etc. Class 11 Biology chapter 10 notes cover all the important concepts of chapter cell cycle and cell division in easy and simple language. Having revision notes and NCERT Solutions for Class 11 Biology Chapter 10 handy is beneficial to save you time. The NCERT Class 11 Biology chapter 10 notes PDF can be downloaded through the link given below.

Cell Cycle and Cell Division Class 11 notes Biology Chapter 10 also covers all the important headings of NCERT textbook that are useful in competitive exams. Chapter 10 Cell Cycle and Cell Division Notes help you revise these crucial concepts given in the NCERT Book in a short period of time during CBSE Board exam preparation. Download the CBSE Notes for Class 11 Biology Chapter 10 PDF and use them offline anywhere. It can be downloaded through the link. Students must go through each topic in cell cycle and cell division Class 11 notes biology in the easiest and most effective way possible with the help of NCERT Notes for Class 11. Check the given Class 11 Biology Notes Chapter 10 Cell Cycle and Cell Division PDF for quick revision.

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

Cell

Cells, like all living creatures, have the ability to grow and reproduce. All cells split into two daughter cells each time they divide, with each parental cell producing two daughter cells. These freshly generated daughter cells can grow and divide, forming a new cell population from the growth and division of a single parent cell and its progeny. To put it another way, such growth and division cycles enable a single cell to expand into a complex with millions of cells.

Cell Cycle and Cell Division Class 11 notes tell us that the cell cycle is a series of processes that occur in a cell as it divides and expands. A single cell goes through many cell cycles before becoming a multicellular creature. A cell spends the majority of its time in interphase, which is when it grows, duplicates its chromosomes, and prepares to divide. After that, the cell exits interphase, goes through mitosis and completes its division. According to notes on Biology for Class 11 chapter 10 For growth, repair, and reproduction, cell division is required.

Cell Cycle

• The cell cycle is a series of events that occur during the life of a cell. In all living organisms, cell division is a crucial activity.
• During cell division, DNA replication and cell growth happen at the same time. To ensure proper division and formation of progeny cells with intact genomes, all of these processes, namely cell division, DNA replication, and cell growth, must be coordinated.
• The cell cycle is the process through which a cell replicates its genome, synthesizes other cell parts, and eventually splits into two daughter cells.
• Interphase and M-phase are the two phases of the cell cycle. While cell growth (in terms of cytoplasmic expansion) is a continuous process, DNA synthesis occurs only once during the cell cycle.
• During cell division, a complex series of events distribute the replicated chromosomes (DNA) to daughter nuclei. These occurrences are genetically influenced.
• The length of the cell cycle, however, varies from organism to organism and from cell type to cell type. Yeast, for example, can complete the cell cycle in less than 90 minutes. Some cells do not go through a gap phase in their cell cycle, while others spend the majority of their life in it.

Phases of Cell Cycle

Interphase and M-phase are the two phases of the cell cycle. During interphase, the cell grows or rests depending on the situation. M-phase is the time when the cell division occurs.

Interphase

• The stage between two subsequent cell divisions is known as interphase.
• It is the longest phase of the cell cycle, during which the cell is extremely active and prepares for cell division. G1 -phase, S -phase, and G2 -phase are the three sub-phases of the interphase.
• The interphase takes up more than 95% of the cell cycle's time.
• The interphase, also known as the resting phase, is the time when the cell prepares for division by going through an organized process of cell growth and DNA replication.
• The interphase is further broken into three phases:

• G1 phase (Gap 1)
• S phase (Synthesis)
• G2 phase (Gap 2)

G1 phase (Gap 1):

The G1 phase is the time between mitosis and the start of DNA replication. The cell is metabolically active and expands continually during the G1 phase, but it does not duplicate its DNA.

S phase (Synthesis):

The S phase, also known as the synthesis phase, is the time when DNA is synthesized or replicated. The amount of DNA per cell doubled throughout this time. If the starting amount of DNA is 2C, it will increase to 4C. However, the chromosome number does not grow; if the cell had diploid or 2n chromosomes at G1, the number of chromosomes remains the same after the S phase, i.e. 2n.

In animal cells, DNA replication begins in the nucleus during the S phase, while the centriole duplicates in the cytoplasm.

G2 phase (Gap 2):

Proteins are synthesized in preparation for mitosis during the G2 phase, while cell development continues. Some cells in mature animals do not appear to divide (e.g., heart cells), while many others divide only when necessary to replace cells that have been lost due to damage or cell death. These cells that do not divide further depart the G1 phase and reach the quiescent stage (G0) of the cell cycle, which is a dormant stage of the cell cycle. Cells in this stage are still metabolically active, but they no longer proliferate unless they are required to do so by the organism.

M-phase (Mitosis phase) or Division Period

The M phase is the period during which a cell divides or undergoes mitosis. This is the cell cycle's most dramatic stage. The letter 'M' stands for mitosis or meiosis, respectively. Karyokinesis and cytokinesis are both involved in M-phase. Cytokinesis is the division of the cytoplasm into two daughter cells, whereas karyokinesis is the division of the nucleus into two daughter nuclei. In a rapidly dividing human cell with a 24-hour cell cycle, M phase takes approximately an hour.

Karyokinesis

Karyokinesis involves the following four stages:

• Prophase

• Metaphase

• Anaphase

• Telophase

Prophase:

Prophase, the first stage of mitosis karyokinesis, occurs after the S and G2 phases of interphase. The new DNA molecules generated in the S and G2 stages are not separate, but rather interconnected. The onset of chromosomal material condensation characterizes prophase. Each chromosome, which can be seen with its sister-chromatids connected by the centromere, becomes visible under a light microscope due to condensation. The nucleolus begins to go away. The nuclear membrane gradually disintegrates and vanishes. The centrosome, which had been duplicated during interphase, begins to migrate towards the cell's opposite poles.

Metaphase:

The second phase of mitosis begins when the nuclear envelope completely disintegrates and the chromosomes are distributed throughout the cell's cytoplasm. Chromosome condensation is complete at this point and they may be seen clearly under the microscope. The chromosomes have been condensed to the point where they appear to be extremely short. Sister chromatids and centromeres take the stage. In the equatorial plane of the cell, all chromosomes are found. The metaphase plate is the term for this. The mitotic spindle has completed its development. Each chromosome's centromere is divided into two halves, each of which is associated with a chromatid.

Anaphase:

Each chromosome's chromatids separate to generate two chromosomes known as daughter chromosomes. The spindle apparatus pulls the produced chromosomes away in the opposite direction. During mid-anaphase, chromosomes being dragged out resemble a cluster of bananas. Anaphase ends when each set of chromosomes reaches opposing poles of the cells.

Telophase:

The telophase is the last stage of mitosis. The centromeres with their chromosomes at the poles begin to uncoil, lengthen, and lose their uniqueness. The nucleolus starts to emerge again. Around the chromosomes, the nuclear membrane begins to emerge. Spindle threads disintegrate and are absorbed by the cytoplasm. In this way, a cell produces two daughter nuclei.

Cytokinesis

• The division of the cytoplasm into two daughter cells is referred to as cytokinesis. A constriction marks the beginning of the division.
• This constriction deepens over time, eventually joining in the Centre and dividing cytoplasm into two daughter cells.
• The process of cytoplasmic division is perpendicular to the spindle. This cytokinesis mechanism is only found in animal cells. Plant cells, on the other hand, have a moderately rigid cell wall. Furrow formation is impossible as a result of this. Instead, the cell wall/partition begins at the cell's Centre and spreads outward to meet the existing lateral walls.
• The creation of the new cell wall starts with the formation of a basic precursor known as the 'cell-plate,' which symbolizes the middle lamella between two adjacent cells' walls.
• Organelles such as mitochondria and plastids are dispersed between the two daughter cells during cytoplasmic division.

Significance of Mitosis:

Because mitosis is an equational division, the number of chromosomes remains constant. It ensures a quantitative and qualitatively balanced distribution of nuclear and cytoplasmic material between daughter cells. Hereditary material (DNA) is also distributed evenly. It aids in the development and growth of organisms. Mitosis makes a substantial contribution to cell repair. The cells of the epidermis' upper layer, the cells of the stomach lining, and blood cells are all regularly replaced. Plants grow continuously throughout their lives due to mitotic divisions in the meristematic tissues - the apical and lateral cambium.

MEIOSIS:

• The fusion of two gametes, each with a complete haploid set of chromosomes, is required for the creation of offspring by sexual reproduction. Specified diploid cells are used to make gametes.
• The formation of haploid daughter cells is achieved through a specialized type of cell division that reduces the number of chromosomes by half. Meiosis is the technical term for this type of division, which is also known as reductional division.
• In the life cycle of sexually reproducing organisms, meiosis ensures the generation of the haploid phase, whereas fertilization restores the diploid phase. Meiosis is a process that occurs during gametogenesis in both plants and animals.
• Meiosis is made up of two nuclear and cell division cycles named meiosis I and II, but only one DNA replication cycle.
• After the parental chromosomes have replicated in the S phase to produce identical sister chromatids, meiosis I begins.
• Meiosis involves the pairing of homologous chromosomes and recombination between non-sister chromatids of homologous chromosomes.
• At the completion of meiosis II, four haploid cells appear.

Meiosis I:

Prophase I:

• When compared to mitosis, the prophase of the initial meiotic division is often longer and more complex. Based on chromosomal behavior, it has been further classified into the following five phases: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.
• The chromosomes become visible under a light microscope during the leptotene stage. Chromosomes continue to compress throughout leptotene.
• This is followed by zygotene, the second stage of prophase I. During this stage, chromosomes begin to couple together, and this process is referred to as synapsis.
• Homologous chromosomes are chromosomes that are paired in this way. This stage's electron micrographs show that chromosome synapsis is accompanied by the creation of a complex structure known as the synaptonemal complex.
• A bivalent or tetrad is a complex produced by a pair of synapsed homologous chromosomes. However, at the next step, these become more apparent.
• In comparison to the next stage, pachytene, the first two stages of prophase I are relatively short-lived.
• The four chromatids of each bivalent chromosome become differentiated and appear as tetrads at this stage.
• The emergence of recombination nodules, which are sites where non-sister chromatids of homologous chromosomes cross over, characterizes this stage.
• The exchange of genetic material between two homologous chromosomes is referred to as crossing over. Crossing over is also an enzyme-mediated process, with recombinase being the enzyme involved. Recombination of genetic material on the two chromosomes occurs when crossing over happens.
• By the end of pachytene, recombination between homologous chromosomes has been accomplished, leaving the chromosomes connected at the crossing-over sites.
• Diplotene begins with the dissolution of the synaptonemal complex and the potential of the bivalents' recombined homologous chromosomes to separate from one another except at crossover sites. Chiasmata are these X-shaped structures.
• Diakinesis is the final stage of meiotic prophase I. Chiasmata terminalization is a sign of this.
• The chromosomes are fully condensed during this phase, and the meiotic spindle is put together to prepare the homologous chromosomes for separation. The nucleolus vanishes and the nuclear envelope disintegrates after the end of diakinesis. Diakinesis is the shift from prophase to metaphase.

Metaphase I:

On the equatorial plate, the bivalent chromosomes align. Microtubules from opposing poles of the spindle bind to homologous chromosomes' kinetochore.

Anaphase I:

Sister chromatids remain connected at their centromeres as homologous chromosomes split.

Telophase I:

• The nucleolus and nuclear membrane return, cytokinesis occurs, and the dyad of cells is formed.
• Despite the fact that chromosomes disperse in many circumstances, they never reach the interphase nucleus's very stretched state.

Interkinesis is a short-lived stage between the two meiotic divisions. During interkinesis, DNA is not replicated. Prophase II occurs after interkinesis.

Meiosis II:

Prophase II:

Meiosis II begins soon after cytokinesis, often before the chromosomes have fully lengthened. Meiosis II, in contrast to meiosis I, looks like a regular mitosis. By the end of prophase II, the nuclear membrane is no longer visible. The chromosomes become compact once more.

Metaphase II:

The chromosomes align at the equator at this phase, and microtubules from opposite poles of the spindle attach to the kinetochores of sister chromatids.

Anaphase II:

It starts with the centromeres of each chromosome (which were holding the sister chromatids together) splitting simultaneously, allowing them to migrate toward opposing poles of the cell by shortening microtubules associated with kinetochores.

Telophase II:

In telophase II, when the two groups of chromosomes are enveloped by a nuclear envelope once more, cytokinesis occurs, resulting in the production of four haploid daughter cells, or a tetrad of cells.

Significance of Meiosis:

Gametes are produced through meiotic division. If it isn't present, the number of chromosomes doubles or quadruples, resulting in monstrosities (abnormal forms). Meiosis keeps the number of chromosomes in a species constant from generation to generation. Crossing over results in the exchange of genetic material, resulting in genetic variants, which are the basic ingredients for evolution.

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• Cell Cycle and Cell Division Class 11 notes will help you review the chapter and have a better understanding of the important concepts addressed.
• These Notes for Class 11 Biology chapter 10 are also beneficial for covering the core themes of the CBSE Biology Syllabus in Class 11 as well as for competitive exams such as AIPMT, AIIMS, NEET, and others.
• Class 11 Biology chapter 10 notes pdf download can be utilised for offline preparation.
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