Class 9 Biology Summary

Cell Division

S.H. Kamboh Updated 6 hours ago 1 min read 75 views

Cell division is the process by which a parent cell divides to produce new cells. It is essential for growth, repair, reproduction, and maintaining living organisms.

There are two main types of cell division:

1. Mitosis

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Mitosis produces two genetically identical diploid daughter cells. It occurs in body (somatic) cells and is responsible for:

  • Growth

  • Tissue repair

  • Replacement of worn-out cells

  • Asexual reproduction in some organisms

The stages of mitosis are:

  • Prophase: Chromosomes condense and become visible.

  • Metaphase: Chromosomes align at the cell's equator.

  • Anaphase: Sister chromatids separate and move to opposite poles.

  • Telophase: New nuclear membranes form around each set of chromosomes.

  • Cytokinesis: The cytoplasm divides, producing two daughter cells.

2. Meiosis

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Meiosis produces four genetically different haploid cells (gametes), such as sperm and egg cells. It is important for:

  • Sexual reproduction

  • Maintaining the chromosome number across generations

  • Creating genetic variation through crossing over and independent assortment

Differences between Mitosis and Meiosis

FeatureMitosisMeiosis
Number of divisions12
Daughter cells24
Chromosome numberSame as parent (diploid)Half of parent (haploid)
Genetic makeupIdenticalGenetically different
Occurs inBody cellsReproductive cells

In summary, mitosis is used for growth and repair, while meiosis is used to produce reproductive cells for sexual reproduction.