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CELL DIVISION
Mitosis and Meiosis
CELL SIZE
Why are cells so small?
What causes cells to stop growing and then
to divide?
CELL SIZE

Cell Membrane


Size is measure SA (units2)
Cytosol

Size is measure volume (units3)
As cell size increases, the volume increases far
more rapidly than SA
 If SA:V (ie surface area equals volume) becomes
too small

CELL DUPLICATION
Mitosis
MITOSIS
Growth and repair of plant and animal tissues is
due to cell reproduction
 This reproduction is MITOSIS

Continuous process that divides a cell
 Parent cell divides into two daughter cells
 Each daughter cell has exactly the same
CHROMOSOMES as the parent cell

WHAT DOES THIS DIVISION LOOK LIKE?
Parent Cell
Mitosis Occurs
Daughter Cells
WHAT DOES CHROMOSOMES LOOK LIKE?
THE PHASES OF MITOSIS
INTERPHASE
Period between cell
division
 90% of cell’s life
 Chromosomes are
extended into a
chromatin network
 Chromosomes
replicate themselves
 Interphase is over
when centrioles
migrate to opposite
poles

PROPHASE





Begins when nuclear
membrane starts to
break down
Chromosomes coil into
short, thick, clearly visible
double stranded
chromosomes
Astral rays form from
centrioles
They extend across the cell
becoming spindle fibers
Prophase is over when the
chromosomes begin to
move toward the equator
of the cell
METAPHASE
Chromosomes line up
beside each other at
the equator of the
cell
 Metaphase is over
when each
centromere of a
chromosome
attaches itself to a
spindle fiber

ANAPHASE
The chromatids pull
apart to move to
opposite poles by the
shortening of the
spindle fibers
 Ends when the
chromatids reach
the poles

TELOPHASE




When the chromatids
are at opposite poles the
cell can safely divide in
two
Plant cells and animal
cells divide apart in
different ways
Plant cells, a cell plate
forms down the equator
Cell plate becomes
the missing cell wall
if each daughter cell
TELOPHASE


Animal cells, the cell
membrane pinches
inward until the two
daughter cells separate
Each daughter cell then
prepares for interphase;
chromosomes unwind into
a chromatin network,
nuclear membranes
reform, centrioles move to
form a centrosome
again, organelles are
manufactured to help the
new cells grow to
mature size
DIFFERENCES BETWEEN PLANT AND
ANIMAL CELL MITOSIS:
1.
Animal cells use centrioles, plant cells do not
2.
Animal cells pinch inwards to separate, plant
cells lay down a cell plate to separate
Mitosis produces a new cell exactly like the
parent cell.
 How does an organism like a human being
develop from a single fertilized egg?



Differentiation
The process that can change a form from an
immature one to a mature one requires 3
different factors:
1.
Each type of cell uses only certain info from the
chromosomes
2.
Neighbouring cells influence each other
3.
The cells environment is an influence
EX) Scars