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Transcript
Cell Growth and Division
How do we grow?
Is each cell getting larger?
Or
Are there more cells?
Living things grow by producing more
cells!
Why can’t we just have larger cells?
Why is it necessary for our cells to divide?
Remember…
How is the cell controlled?
How does the cell know what to do?
How does the cell get nutrients?
How does the cell remove wastes?
Quick Review
With a partner, define the following terms:





Nucleus
Chromosomes
DNA
Cell membrane
Diffusion
Limits to Cell Growth
The larger the cell becomes, the more
demands the cell places on its DNA and
the more trouble the cell has moving
enough nutrients and wastes across the
cell membrane.
DNA “Overload”
DNA = information found in the nucleus that
controls a cell’s function
When a cell is small, the information stored
in the DNA is able to meet the cell’s needs
When a cell gets larger, it does not make
more DNA and the DNA is no longer able to
meet the large cell’s needs resulting in an
“information crisis”
DNA
Exchanging Materials
Nutrients and waste diffuse through the cell
membrane.
The rate of this exchange depends on the
surface area of the cell
But the rate of using nutrients and
producing wastes depend on the volume of
the cell.
Surface Area & Volume
As a cell increases in size, the volume
increases more rapidly than the surface
area, so the ratio of volume to surface
area decreases creating a problem.
As the cell grows larger, it will be difficult
for the cell to get enough nutrients and
release wastes as quickly as they are
needed or produced by the cell.
Surface Area by Volume Ratio
Divide Surface area by Volume to get a
ratio.
Volume increases much more rapidly than
surface area.
Cell Division
Before a cell becomes too large, it divides to
form two cells.
The two new cells are called daughter cells.
The process by which the cell divides into two
new daughter cells is called cell division.
Why divide?
DNA: Before the cell divides, it replicates (copies)
all of its DNA, so each new daughter cell gets one
complete copy of genetic information and there is no
shortage.
Material Exchange: Each new daughter cell has an
increased ratio of surface area to volume, so
enough materials may be exchanged based on the
demands of the cell.
Why else must things reproduce?
Cellular Reproduction
Reproduction – the life process by which living things
produce other living thing of the same species
It is necessary for the survival for the species
Two types of Reproduction through cell division:


Sexually reproducing organisms go through mitosis and meiosis
Asexually reproducing organisms only go through mitosis
What about me?
At this very moment, group of cells in your
body are growing, dividing, and dying.
Worn out skin is being replaced and
bruises are healing.
Red blood cells are being produced in
your bones at a rate of 2 to 3 billion to
replace those that wear out.
http://video.google.com/videoplay?docid=-7204725871954420481
Review the cycle
Organisms go through stages, or a life
cycle, while they are alive. A simple
cycle consists of birth, growth and
development, and death.
In cell division, the nucleus divides and
then the cytoplasm divides to form two
new daughter cells.
The cell cycle is a series of events that
takes place in a cell from one division to
the next.