Cell division is the process by which a parent cell divides into two or more daughter cells. It is the means by which organisms grow, repair damaged tissues, and reproduce. There are three types: amitosis, mitosis, and meiosis.
Cell division is a fundamental process of life. All cells arise from pre-existing cells — this principle was stated by Rudolf Virchow as "Omnis cellula-e cellula." The cell cycle describes the sequence of events from one cell division to the next and consists of two main phases: interphase and the M phase (mitotic phase).
Interphase is the phase between two successive cell divisions and accounts for about 95% of the cell cycle duration. It consists of three sub-phases: G1 phase (cell grows, organelles are synthesized), S phase (DNA replication occurs — each chromosome now has two sister chromatids), and G2 phase (cell prepares for division, proteins needed for mitosis are synthesized).
Some cells exit the cell cycle after G1 and enter a quiescent stage called G0 phase. Cells in G0 do not divide — examples include neurons and mature red blood cells. This is an important concept for NEET as it explains why nerve and heart muscle cells don't regenerate.
The M phase includes mitosis (nuclear division) and cytokinesis (cytoplasmic division). Mitosis is equational division producing two identical diploid cells, while meiosis is reductional division producing four different haploid cells.
Amitosis is the simplest form of cell division, where the nucleus divides directly by constriction without spindle formation or chromosome condensation. It occurs in prokaryotes, some protists, and in certain specialized cells like the endosperm cells of angiosperms.
The cell cycle is regulated by cyclins and cyclin-dependent kinases (CDKs). Cancer results from uncontrolled cell division due to failure of cell cycle regulation — this is why understanding cell cycle control is medically important.
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