Transcript Cell Reproduction-
Why do cells reproduce at all?
Couldn’t they grow really, really big?
• Cells are limited to small sizes, therefore
they must reproduce to make many cells
instead of one big cell.
• Reasons why big cells are bad include:
– Diffusion would be too slow.
– Too many proteins would be needed.
– Cell membrane (surface area of cell) would
not be able to increase as fast as the cell
volume and would not work properly. (volume
= l x w x h; surface area = l x w x 6)
Review: all cells come from
• This means that when a cell reproduces or
divides, it creates two cells that are identical to
• This occurs not only because it is better to have
many small cells, but also because an organism
needs to grow or replace dead tissue. (This also
will cause population growth in unicellular
Chromosomes carry the coiled
The Cell Cycle
• The cell cycle is the steps a cell goes
through during its life.
• First, there is a period of growth and DNA
replication called interphase. Most of a
cell’s life is spent in this stage.
• After this, the cell divides, or reproduces,
in a series of steps called mitosis. After
this 2 identical cells are formed, each with
complete set of chromosomes.
Steps of Mitosis
• **use the terms to provide clues for what
happens in each step**
• First and longest step.
• Chromatin (DNA) coils into
• The two halves are identical,
and are called sister
chromatids. They are held
together by the centromere.
• By the end of prophase the
nuclear membrane is
• In animal cells, centrioles and
spindle fiber have formed and
are lining up in the cell.
become attached to
the spindle fibers at
• Spindle fibers help to
chromosomes in the
middle of the cell, so
each sister chromatid
is facing a pole.
• Chromatids reach
opposite poles and begin
• Two new nuclei are
formed at the poles.
• A new cell membrane
begins to form down the
middle of cell. This
divides the cytoplasm and
organelles and is called