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Types of Cell Division

Cell cycle of Class 11

  1. Mitosis takes place when new cells are added to multicellular organisms as they grow and when tissues are repaired or replaced. Root tips (root meristem) of onion (Allium cepa, 2n = 16) are the best plant  material for the study of mitosis in labs. Root tips of Vicia faba (broad bean) are also used. In animals, cells at the base of the nails, bone marrow cells, and skin cells (stratum germinativum) are taken to study mitosis.
  2. Meiosis occurs in the production of gametes by organisms that reproduce sexually. The best material to study meiosis in the classroom is anthers from young unopened buds (buds before anthesis) of Tradescantia and onion and testes of Grasshopper.
  3. Aceocarmine is a nuclear basic stain used to study the cell division in plant material.

Factors Controlling Cell Divison

  1. Cell Size When cells grow in size, their nucleo-cytoplasmic ratio, and surface area-volume ratio decrease. To maintain these ratios cells divide as smaller cells have high ratios, therefore more active.
  2. Mitogens are polypeptide growth factors that control cell proliferation. A common plant mitogen is the hormone cytokinin. Mitogens in human beings include lymphokines, Epidermal growth factor (EGF), or platelet-derived growth factors. (PDGF)

Generation time : Period between two successive divisions.

Cell Cycle: The entire sequence of events which takes place in a cell between one cell division and the next.

Three major events of the cell cycle are

  • Replication of DNA
  • Karyokinesis (Nuclear division)
  • Cytokinesis (Cytoplasmic division)

Cell Cycle consists of

  1. Long nondividing – I-phase
  2. Short dividing – M-phase
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