Transcript mitosis - Free Exam Papers

MITOSIS
MITOSIS
Primary purpose is to increase the number
of cells
 Daughter cells are genetically identical to
the parents
 Occurs during growth and asexual
reproduction.
 Mitosis is a continuous process which is
divided for convenience into a number of
stages.

MITOSIS
Interphase
 Sometimes called the
“resting stage” between
divisions
 BUT cells are
metabolically very active
 The amount of DNA in the
nucleus doubles
 New organelles such as
mitochondria are made.
MITOSIS
Interphase
 No chromosomes are
visible
 The chromosome
material, chromatin,
is spread through the
nucleus in a diffuse
form.
MITOSIS
Prophase
The longest stage
 Chromosomes become
visible
 In animal cells, the
centrioles divide and
move to opposite ends
of the nucleus
MITOSIS
Prophase
 Protein microtubules
develop from each
centriole forming
spindle fibres.
 (In plant cells there are
no centrioles and the
spindle forms
independently)
MITOSIS
Prophase
 Towards the end of
prophase each
chromosome can be
seen to consist of two
chromatids held
together by a
centromere.
MITOSIS
Prophase
 At the end of prophase
the nucleolus
disappears and the
nuclear envelope
breaks down.
MITOSIS
Metaphase
 Chromosomes line up
on the equator of the
spindle.
 They attach
themselves to the
spindle by their
centromere
MITOSIS
Anaphase
 The centromeres
divide
 The free chromatids
move to the poles
MITOSIS
Anaphase
 This movement results
from the contraction
of the spindle fibres.
 As they shorten they
pull the chromatids
apart.
MITOSIS
Telophase
 The chromatids have
reached the poles and
are now regarded as
distinct chromosomes
again.
 A nuclear envelope
forms around each
group of chromosomes
MITOSIS
Telophase
 The chromosomes
uncoil returning to
chromatin
 The cytoplasm divides
by cytokinesis.
CYTOKINESIS
Animal cells
 The centre of the cell
‘pinches in’ to form a
division furrow.
 As the division
deepens, the cell
surface membrane on
each side joins up.
 Two separate cells
result.
CYTOKINESIS
Plant cells
 Vesicles produced by the Golgi body collect
on equator of cell
 These vesicles fuse to form a cell plate.
 The cell plate eventually stretches right
across the cell forming the middle lamella.
 Cellulose builds up on lamella to form cell
walls.
CYTOKINESIS