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CBSE Quick Revision Notes (Class-11 Biology)
CHAPTER-10 CELL CYCLE AND CELL DIVISION
•The sequence of events by which a cell duplicates its genome, synthesizes the other
constituents of cells and eventually divides into two daughter cells is called cell cycle.
•DNA synthesis occurs in one specific stage of cell division but distribution of chromosome in
cells occurs in complex series of events during cell division.
Phases of Cell cycle
Human cell divides once in approximately 24 hours, which may
vary in different organisms. In yeasts it takes about 90 minutes
to complete the cell division process.
Cell cycle is divided into two basic phases-
a. Interphase- it is the phase between two successive M phases.
Interphase lasts for 95% of a cell cycle. This phase is called as
resting phase but during this period the cells prepare its self
for nuclear division by cell growth.
b. M Phase- when the actual cell division or mitosis occurs. It
starts with karyokinesis (nuclear division) or duplication of chromosome and end with
cytokinesis or division of cell matrix (cytoplasm division).
•G1 phase represents the interval between
mitosis and initiation of DNA replication.
Cell is continuously active and grows in
size.
•During synthesis phase, replication or
synthesis of DNA takes place and amount of DNA get doubles per cell.
•During G
2
phase protein is synthesized in preparation for mitosis.
•In adult animals, some cells do not divide or may divide occasionally. These cells do not
divide further and exists the G
1
phase to enter an inactive stage called Quiescent Stage (G
0
)
of cell cycle.
•In animals mitotic division is present in only somatic diploid cells but in plants it is seen in
both haploid and diploid cells.
•Mitosis cell division is also known as equational division because the numbers of
chromosome remain same in parental and progeny cells.
