Chapter 10 –
Cell Growth and Division
Section 10-1: Cell Growth
Organisms become larger because they produce more
cells, not because the cells themselves get bigger
There are 2 main reasons why cells
divide instead of getting bigger;
DNA & nutrient and waste movement
1. The larger the cell = the more demands on the cell’s
DNA
The cell only has so much DNA
and when the cell is small it can
meet all of its needs
More DNA is usually not created
even if a cell gets larger, so the
initial amount of DNA isn’t
enough to meet the larger needs
2. The larger the cell = the more trouble moving nutrients
and waste across the cell membrane
Exchange of food, water,
waste, and oxygen depend on
the cell membrane (the surface
area)
The rate at which cells use
food and produce waste
depend on the cell’s volume,
not the surface area
Volume increases faster than surface area does, so
eventually if the cell got large enough, there would
be more volume than surface area and it wouldn’t
be able to regulate food and waste properly.
Before a cell becomes too large to function, the
cell divides forming two “daughter” cells
Before division, a cell will
copy all of its DNA to make
sure the two new cells have
the same DNA
Cell division = the process
of dividing to form two
“daughter cells”
Section 10-2:
Cell Division
In cell division, each daughter cell needs to have the
same contents  this takes some prep work
In prokaryotes, cell division is
pretty simple: just separate the
cell contents into two equal parts
In eukaryotes, cell division is more complex and
happens in two main stages; mitosis and cytokinesis
Mitosis occurs in the
nucleus of the cell
It is the source of new cells
when an organism grows
and develops
Cytokinesis occurs in the
cytoplasm
Chromosomes are important when it comes to passing
on DNA to daughter cells
Chromosomes are made up
of DNA  it carries the
cell’s genetic code
The number of chromosomes
present is important, each
type of organism has a specific
number of chromosomes
Normally, DNA is spread through the nucleus, but
during cell division chromosomes condense
Before cell division happens, each
chromosome is replicated  this
means that each chromosome
consists of two “sister” chromatids
Since “sister” chromatids contain
the same information, during cell
division the “sister” chromatids
separate into 2 different cells
Centromeres = what keep
the chromatids attached to
each other before division
The cell cycle is the series of events that cells go through
as they grow and divide
During the cell cycle, a cell
grows, prepares for division,
and divides to form two
daughter cells, which both
start the cycle over again
The cell cycle consists of 4
phases; M phase, G1 phase,
S phase, and G2 phase
1. M phase: mitosis and cytokinesis take place
2. G1 phase: the cell experiences a good deal of cell
growth (an increase in size, new organelle production)
3. S phase: chromosomes are replicated (synthesized)
4. G2 phase: the shortest phase, the cell prepares for
mitosis to happen
The G1, S, and G2 phases all
make up interphase = a period
in between cell divisions
Mitosis is a phase in the cell cycle, but is also
broken up into 4 phases;
prophase, metaphase, anaphase, and telophase
Prophase: the first and longest phase of mitosis
Chromosomes become visible as
they start to condense
Centrioles separate and take a
position on opposites sides of
the nucleus
Spindle fibers start to form
The centromeres of each set of
chromotids attach to the spindle fibers
Towards the end of prophase,
the nucleous disappears and the
nuclear envelope breaks down
Metaphase: the second phase that
may only last a few minutes
Chromosomes line up
across the center of the cell
Anaphase: the third phase of mitotis
The centromeres connecting sister
chromatids split  the sister
chromatids can now separate and
become their own chromosome
The chromosomes move
away from each other and
move toward the centrioles
When the chromosomes stop
moving, anaphase ends
Telophase: the last phase of mitosis
The separated chromosomes start to
disperse (they aren’t dense any more)
The spindle breaks apart
A nuclear envelope starts
to form around each
cluster of chromosomes
Cell division and the cell cycle end with cytokinesis
Cytokinesis = the division
of the cytoplasm of the cell
to create the two new cells
Cytokinesis usually happens
at the same time as telophase
In animal cells, the cell
membrane gets pinched
in and creates 2 cells
In plant cells, a cell plate
forms between the nuclei
 it eventually turns into
a separating membrane
Section 10-3:
Regulating the Cell Cycle
Cell growth and division are controlled
very carefully in the human body
Not all cells move through the cycle at
the same rate, and some developed
cells do not even undergo division
Controls for cell division can be turned on and off
Cells grown in a culture will
continue to grow until they
If some of the cells are
come into contact with
removed, the cells
respond by growing
another cell  at that point
they stop growing
again to fill in the gaps
The idea of control can be seen in
the human body  when you get
a cut, your cells respond by rapid
growth to fill in the cut, or heal
Cyclins regulate the timing of the
cell cycle in the eukaryotic cell
Cyclins are proteins that rise and
fall in numbers, depending on
where a cell is in the cell cycle
If you inject cyclin into a
nondividing cell, it will
start to divide
More recently, dozens of other proteins were found that
regulate the cell cycle
They are separated into two
categories; those that occur
inside the cell and those that
occur outside the cell
Internal regulators are found inside the
cell and basically serve to double check
each step of mitosis
External regulators are found
outside the cell and help speed
up and slow down the cell cycle
Growth factors are important
external regulators  they help
with embryonic development
and healing
Neighboring cells help to slow
down cell growth so that tissues
don’t disrupt each other
Cancer cells do not respond to the signals that
regulate the growth of most cells
Cancer cells divide
uncontrollably and form tumors
The control of the cell cycle is broken
down by something (anything from
smoking, to excessive radiation, to
viral infections)
A lot of cancer cells have a defect in a gene
called p53  it normally stops the cell cycle
until all chromosomes have been replicated
Cancer is an example of why the
cell cycle is so important