XI Biology Topic- Cell Cycle. Study material for NEET,CET. It includes phases of cell cycle -Interphase and M-phase described in detail with images.

1. Cell Cycle &
Division
Mrs.Tarini Joshi
M.Sc.,M.Ed., NET,SET

2. Cell Division
Cell division is imp for growth
and differentiation.
The division is achieved by
Karyokinesis and cytokinesis.
Differentiation of cell leads to
organ development.
Organ into organism.
Tissues like Bone marrow
,germinal tissue and
meristematic region divide
continuously.

3. Cell Cycle
• All cells are produced by division of pre existing
cell.
• The orderly sequence of events by which the cell
duplicates its contents and divides into two is
called as cell cycle.
• All events are genetically controlled.

4. Did You Know!!!
Duration of cell cycle
varies from organism
to organism.
E.g. in Human,24 hrs
In Yeasts, 90 min

5. What is Cell Cycle?
Sequential events occurring in
the life of a cell is called cell
cycle.
There are two phases of cell cycle
as -1. interphase
2. M-phase.

7. Phases of cell cycle
• G1-phase:
• This is also known as first gap period or first
growth period. It starts.
• Interval between mitosis and DNA synthesis.
• immediately after cell division, cell becomes
metabolically active.
• Prepare machinery for DNA Replication.
• Cell performs RNA synthesis (mRNA, rRNA and t-
RNA), protein synthesis and synthesis of
membranes during this phase.
• Regulatory proteins which controls mitosis.
• Enzymes necessary for DNA synthesis.
• Tubulin and other mitotic apparatus.
• 30-50% time
• Time 8 hrs or more

8. S-phase ( Synthetic Phase):
• It is synthesis phase in which DNA is
synthesized or replicated, so that amount
of DNA per cell doubles.
• Chromosome number remains same.
• Histone proteins are also synthesized
during this phase.
• 35-45% time
• In animal cell centrioles duplicate in
cytoplasm.

9. G2phase:
• G2 is the second growth phase, during which
nucleus increases in
volume.
• Metabolic activities essential for cell division
occur during this phase.
• Various proteins necessary for cell division
are continue to synthesized during this phase.
• Besides, RNA synthesis also occurs during
this phase.
• DNA replication stops.
• Organelle duplication
• 10-20% time
• In animal cells, a daughter pair of centrioles
appear near the pre-existing pair.
• Cell prepared for mitosis.

10. G0-phase
• The phase in which cells fail to divide
further (do not undergo S-phase after G1-
phase) and undergo differentiation is known
as G0 phase or quiescent stage.
• It occurs due to non-availability of mitogen
(a substance that induces or stimulates
mitosis) and energy rich compounds.
• The cells remain metabolically active, grow
in size and differentiate for particular
function after attaining a particular shape.
• However, some cells remain in
undifferentiated state as reserve cells. They
may proceed with cell division when
required e.g. fibroblasts; it helps in healing
of wounds and grow and divide again.

11. M-phase or period of division:
1. 'M' stands for mitosis or meiosis.
2. M-phase involves karyokinesis and cytokinesis.
3. Karyokinesis is the division of nucleus into two daughter
nuclei whereas cytokinesis is division of cytoplasm
resulting in two daughter cells.
Types of cell division:
Three kinds of cell division are found in animal cells. They
are –
1. amitosis or direct division
2. mitosis or indirect division
3. meiosis or reduction division.

12. Amitosis: Amitosis, also known as direct cell division, is a simple form of cell
division where a single cell divides into two without involving the complex
processes of mitosis or meiosis. This division occurs without the formation of
a spindle apparatus or the nuclear changes seen in mitosis.

13. Mitosis: Mitosis is a type of cell division that occurs in somatic cells (non-
reproductive cells) and results in the formation of two genetically identical
daughter cells, each having the same number of chromosomes as the parent
cell.

14. Meiosis:
Meiosis is a specialized type of cell
division that occurs in reproductive cells
(germ cells) and results in the formation
of four non-identical haploid daughter
cells, each containing half the number of
chromosomes as the parent cell.

15. Questions
Define cell cycle.
Organelle duplication takes place in……….
DNA replication takes place in …..
Centriole duplication takes place in ……
Explain in detail phases of cell cycle.
Sketch and label cell cycle.
Differentiate between mitosis and amitosis.

16. References –
NCERT Text book of Biology
H.Sc. Text book of Biology
http//: google images.com