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Cell Cycle and Cell Division Class 11 Notes Biology Chapter 10

1. Introduction: It is the process by which a mature cell divides and forms two nearly equal daughter cells which resemble the parental cell in a number of characters.
2. Discovery: Prevost and Dumas (1824) first to study cell division during the cleavage of zygote of frog.
3. Nagelli (1846) was the first to propose that new cells are formed by the division of pre-existing cells.
4. Rudolf virchow (1859) proposed “omnis cellula e cellula” and “cell lineage theory”.
5. A cell divides when it has grown to a certain maximum size which disturb the karyoplasmic index (KI)/Nucleoplasmic ratio (NP)/Kernplasm connection.
6. Two processes take place during cell reproduction.

  • Cell growth: (Period of synthesis and duplication of various components of cell).
  • Cell division: (Mature cell divides into two cells).

7. Cell cycle: Howard and Pelc (1953) first time described it. The sequence of events which occur during cell growth and cell division are collectively called cell cycle. Cell cycle completes in two steps:

  • Interphase
  • M-phase/Dividing phase
    (i) Interphase: It is the period between the end of one cell division to the beginning of next cell division. It is also called resting phase or not dividing phase. But, it is actually highly metabolic active phase, in which cell prepares itself for next cell division. In case of human beings it will take approx 25 hours. Interphase is completed in to three successive stages.
    Cell Cycle and Cell Division Class 11 Notes Biology Chapter 10
    (a) G1 phase/Post mitotic/Pre-DNA synthetic phase/Gap Ist
    (b) S-phase/Synthetic phase
    (c) G2-phase/Pre mitotic/Post synthetic phase/gap-IInd
    (ii) M-phase/Dividing phase/Mitotic phase
    (a) Nuclear division i.e. karyokinesis occurs in 4 phases – prophase, metaphase, anaphase and telophase. It takes 5-10% (shortest phase) time of whole division.
    (b) Cytokinesis: Division of cytoplasm into 2 equal parts. In animal cell, it takes place by cell furrow method and in plant cells by cell plate method.

8. Duration of cell cycle: It depends on the type of cell and external factors such as temperature, food and oxygen. Time period for G1, S, G2 and M-phase is species specific under specific environmental conditions. e.g. 20 minutes for bacterial cell, 8-10 hours for intestional epithelial cell, and onion root tip cells may take 20 hours.
9. Regulation of cell cycle: Stage of regulation of cell cycle is G1 phase during which a cell may follow one of the three options.

  • It may start a new cycle, enter the S-phase and finally divide.
  • It may be arrested at a specific point of G1 phase.
  • It may stop division and enter G0 quiscent stage. But when conditions change, cell in G0 phase can resume the growth and reenter the G1 phase.

10. Cell division is of three types, Amitosis, Mitosis and Meiosis.
11. Difference between cell Mitosis and Meiosis

Cell Cycle and Cell Division Class 11 Notes Biology Chapter 10
Cell Cycle and Cell Division Class 11 Notes Biology Chapter 10
Cell Cycle and Cell Division Class 11 Notes Biology Chapter 10
Cell Cycle and Cell Division Class 11 Notes Biology Chapter 10
Cell Cycle and Cell Division Class 11 Notes Biology Chapter 10
Cell Cycle and Cell Division Class 11 Notes Biology Chapter 10


12. Types of Mitosis

  • Anastral mitosis: It is found in plants in which spindle has no aster.
  • Amphiastral mitosis: It is found in animals in which spindle has two asters, one at each pole of the spindle. Spindle is barrel-like.
  • Intranuclear or Promitosis: In this nuclear membrane is not lost and spindle is formed inside the nuclear membrane e.g. Protozoans (Amoeba) and yeast. It is so as centriole is present within the nucleus.
  • Extranuclear or Eumitosis: In this nuclear membrane is lost and spindle is formed outside nuclear membrane e.g. in plants and animals.
  • Endomitosis: Chromosomes and their DNA duplicate but fail to separate which lead to polyploidy e.g. in liver of man, both diploid (2N) and polyploid cells (4N) have been reported. It is also called endoduplication and endopolyploidy.
  • Dinomitosis: In which nuclear envelope persists and microtubular spindle is not formed. During movement the chromosomes are attached with nuclear membrane.

Types of meiosis: On the basis of time and place, meiosis is of three types

  • Gametic/Terminal meiosis: In many protozoans, all animals and some lower plants; meiosis takes place before fertilization during the formation of gametes. Such meiosis is described as gametic or terminal.
  • Zygotic or Initial Meiosis: In fungi, certain protozoan groups, and some algae fertilization is immediately followed by meiosis in the zygote, and the resulting adult organisms are haploid. Such a meiosis is said to be zygotic or initial. This type of life cycle with haploid adult and zygotic meiosis is termed the haplontic cycle.
  • Sporogenetic Meiosis
    (a) Diploid sporocytes or spore mother cells of sporophytic plant, undergo meiosis to form the haploid spores in the sporangia.
    (b) Haploid spore germinates to form haploid gametophyte which produces the haploid gametes by mitosis.
    (c) Haploid gametes fuse to form diploid zygote which develops into diploid sporophyte by mitotic divisions. e.g.  in higher plants like pteridophytes, gymnosperms and angiosperms.
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FAQs on Cell Cycle and Cell Division Class 11 Notes Biology Chapter 10

1. What is the cell cycle and why is it important for cell division?
Ans. The cell cycle refers to the sequence of events that occur in a cell, including growth, DNA replication, and division into two daughter cells. It is important for cell division as it ensures the proper distribution of genetic material and the formation of new cells for growth, repair, and reproduction.
2. What are the different phases of the cell cycle?
Ans. The cell cycle consists of four main phases: G1 (gap phase 1), S (synthesis phase), G2 (gap phase 2), and M (mitotic phase). During G1, the cell grows and carries out its normal functions. In S phase, DNA replication occurs. G2 phase is a preparation phase before cell division. Finally, the M phase involves mitosis, where the cell divides into two daughter cells.
3. How is the cell cycle regulated?
Ans. The cell cycle is regulated by a complex network of proteins and checkpoints. Cyclin-dependent kinases (CDKs) and cyclins are key regulatory proteins that control the progression through different phases of the cell cycle. Checkpoints ensure that the cell has properly replicated its DNA and has no DNA damage before proceeding to the next phase.
4. What happens during mitosis?
Ans. Mitosis is a process of cell division where a single cell divides into two identical daughter cells. It consists of several stages: prophase, metaphase, anaphase, and telophase. During prophase, the chromosomes condense, the nuclear envelope breaks down, and the spindle apparatus forms. In metaphase, the chromosomes align at the center of the cell. Anaphase is characterized by the separation of sister chromatids, which are pulled towards opposite poles of the cell. Finally, in telophase, the nuclear envelopes reform, chromosomes decondense, and the cell physically divides through cytokinesis.
5. What are the consequences of abnormal cell cycle regulation?
Ans. Abnormal cell cycle regulation can lead to various consequences, including uncontrolled cell division and the formation of tumors. When the cell cycle is not properly regulated, cells may continue to divide without control, leading to the formation of cancerous tumors. On the other hand, if the cell cycle is halted or slowed down, it can result in impaired tissue growth and repair, as seen in certain genetic disorders or delayed wound healing.
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