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Revision: Cell: Structure and Function >> Cell Cycle and Cell Division Biology Science (English Medium) Class 11 CBSE

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Definitions [5]

Definition: Centromere

The two sister chromatids remain attached to each other at a small region called centromere.

Definition: Spindle Fibres

A number of fibres appear between the two daughter centrioles, which are called the spindle fibres.

Definition: Karyokinesis

All the nuclear changes that occur during cell division are collectively termed karyokinesis (karyo: nucleus).

Definition: Cytokinesis

The division of cytoplasm to form two daughter cells after nuclear division is called cytokinesis.

 
Definition: Cell Cycle

The cell cycle is a series of events that take place in a cell leading to the duplication of its DNA and the subsequent division of the cell to produce two daughter cells.

Key Points

Key Points: Karyokinesis

Karyokinesis is the division of the nucleus during mitosis, ensuring equal distribution of chromosomes into two daughter nuclei.
It occurs in four continuous phases:

  1. Prophase – Chromosomes condense and become visible; nuclear membrane and nucleolus disappear; spindle fibres form.
  2. Metaphase – Chromosomes align at the cell's equator and attach to spindle fibres via centromeres.
  3. Anaphase – Centromeres split; sister chromatids separate and move to opposite poles.
  4. Telophase – Chromatids decondense into chromatin; nuclear envelope and nucleolus reappear around each set of chromosomes.
Key Points: Cytokinesis
  • Cytokinesis is the division of the cytoplasm that follows nuclear division (karyokinesis), resulting in the formation of two separate daughter cells.
  • In animal cells, it occurs by the formation of a cleavage furrow, while in plant cells, a cell plate forms at the centre to divide the cytoplasm.
Key Points: Cell Cycle
  1. The cell cycle is a series of steps by which a cell grows, duplicates its DNA, and divides to form two daughter cells.
  2. It has two main phases: Interphase (growth and preparation) and M-phase (mitosis or actual division).
  3. This cycle ensures orderly cell growth, DNA replication, and equal distribution of genetic material.
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