Download f211 1.1.3 cell division

Module 1 - Cells
1.1.3 Cell Division
•
State that mitosis occupies only a small percentage
of the cell cycle and that the remaining percentage
includes the copying and checking of genetic
information.
•
Explain the significance of mitosis for growth, repair
and asexual reproduction in animals and plants.
•
Describe, with the aid of diagrams, the stages of
mitosis.
The Cell Cycle
Each cell goes through a
regular life cycle, similar to
the cycle of life in humans.
The major cell stages are
interphase, mitosis, and
cytokinesis.
Interphase

Interphase consists of:
G1 = growth and preparation of the chromosomes
for replication, new cell organelles are synthesised
(approx 10 hours).

S = synthesis of DNA, amount of DNA doubles (approx

G2 = preparation for mitosis, centrioles replicate and
spindle starts to form (approx 4 hours).
9 hours).
When a cell is in any phase of the cell cycle other
than mitosis, it is often said to be in interphase.
Interphase
A normal resting cell
exists in a state called
interphase in which the
chromatin is
undifferentiated in the
heavily-stained nucleus.
Interphase
Before the cell enters
the mitosis phase, it first
undergoes a synthesis
or S phase where each
chromosome is
duplicated and consists
of two sister
chromatids joined
together by a specific
DNA sequence known
as a centromere.
Mitosis
Mitosis is cell
division.
 The genetic purpose
of mitosis is to
produce two
daughter cells that
are genetically
identical to the
parent cell.
 Mitosis occupies a
small percentage of
the cell cycle.

Prophase
•Tiny bundles of protein called
centrioles start moving to
opposite ends of the cell.
•The mitotic spindle forms.
•The chromosomes become
shorter and more compact.
•
• Nuclear membrane begins to
disappear.
• At the end of prophase, each
chromosome can be seen to
consist of two chromatids, held
together by a centromere.
Prophase
Metaphase
The chromosomes,
attached to the
spindle by the
centromere, begin to
align along the
equator, halfway
between the spindle
poles.
Metaphase
Anaphase
During anaphase the
sister chromatids
separate and are
moved toward the
poles of the spindle,
centromeres first.
 The movement is a
result of the spindle
fibres contracting
and shortening.

Anaphase
Telophase
Chromosomes uncoil
to become long and
thin.
 The mother cell is
physically divided
into two daughter
cells by cytokinesis.
 New nuclear
membranes are
formed.

Telophase
Why is mitosis important?
Mitosis will result in cells which are exact copies of
the parent cells. The daughter cells will contain the
same number of chromosomes and be genetically
identical to the parent.
Mitosis is needed for:
 Growth – in order to grow new cells must be formed,
identical to original cells.
 Repair of tissues – Damaged cells must be replaced
by identical ones.
 Asexual reproduction – results in offspring being
genetically identical to the parent.
Useful websites for Mitosis

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www.biologycorner.com/bio1/cellcycle.html
www.cellsalive.com/mitosis.htm
micro.magnet.fsu.edu/.../mitosis/mitosis.html
www.johnkyrk.com/mitosis.html
www.biologylessons.sdsu.edu/classes/lab8/g
lossary.html
Mitosis animations:
www.johnkyrk.com/mitosis.html
 http://www.cellsalive.com/mitosis.htm

Meiosis

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
Cell division of the
gametes sperm and
ovum.
Results in 4 haploid
chromosomes
genetically different to
mother cell.
This gives rise to
variation within species.