Cell Division: Cell Cycle and Types of Cell Division | Biology Grade XI

Cell Division

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Cell Division: Cell Cycle and Types of Cell Division | Biology Grade XI

Cell Division: Cell Cycle and Types of Cell Division

Cell Division:

It is a cyclic process in which the division of nucleus is followed by division of cytoplasm as a result daughter cells are formed.

Cell Cycle:

All the changes that take place during cell growth and cell division are called cell cycle. Cell cycle can be divided into following phases

  • Interphase: The stage when cell becomes ready to divide is called interphase. It is subdivided into G1 Phase, G2 Phase, S Phase
  • Karyokinesis: It is the process of division of nucleus. It is subdivided into Prophase, Metaphase, Anaphase, Telophase.
  • Cytokinesis: It is the process of division of cytoplasm.

Types of Cell Division:

1. Amitosis cell division or direct cell division: This cell division takes place in prokaryotic and unicellular eukaryotic animals. During the process, the nucleus becomes elongated. The nucleus divides into two nuclei by forming constrictions. The cytoplasm also divides into two parts and the cell membrane is also constricted. Thus two daughter cells are formed.

2. Mitosis cell divisionThe process of cell division in which al the chromosomes replicate and separate into two groups having equal number of chromosomes as their parent cell. Thus two nuclei are formed. 

3. Meiosis Cell Division: The process of cell division which takes place in a diploid cell and produces four haploid cell is meiosis cell division i.e. Each cell having half the number of chromosomes as that of parent cell.

  • Meiosis I: The meiosis I the division is called reductional division or heterotypic division because the cell divides into two daughter cells having chromosome number half in two daughter cells as that present in the mother cell.
  • Meiosis II: It is called equational division or homotypical division because the cells produced after meiosis I undergo further division to produce four cells where chromosome number remains same as that of parent cells, similar to mitosis.

Differences between mitosis and meiosis:

Mitosis

Meiosis

  1. It occurs in somatic cells
  2. Mitosis division completed only in one division

Prophase

  1. It is very short Synapses is absent
  2. No coiling and no replication takes place
  3. No chiasmata formation takes place No crossing over takes place
  4. No Variation occurs

Metaphase

  1. One metaphasic plate is formed Contromere divides longitudinally

Anaphase

  1. Two chromatids of each chromosome separate and move towards opposite pole
  2. Each chromosome is single stranded

Telophase:

  1. Nucleus id diploid
  2. Two nuclei are formed
  3. Two cells are produced after cytokinesis
  1. It occurs in reproductive cells
  2. Meiosis division is completed in two successive divisions

Prophase

  1. Prophase is very long Subdivided into 5 sub phases
  2. In Zygotene synapses occurs
  3. In Pahcytene homologous chromosome undergo coiling and replication occurs
  4. In diplotene chiasmata formation and crossing over takes place
  5. Variation occurs

Metaphase

  1. Two metaphase plate is formed
  2. Centromere does not divide in Meiosis I but in II

Anaphase

  1. Homologous chromosomes separate and move towards opposite pole
  2. Each chromosome is double stranded n meiosis I

Telophase

  1. Nuclei are haploid
  2. Four nuclei are formed after Telophase II Four cells are produced after cytokinesis II

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