Download Cellular Growth - Biology-RHS

Cellular
Growth
Chapter 9.1
Main Idea
Explain why
cells are
relatively
small in
your notes.
Cells grow
until they
reach their
size limit,
then they
either stop
growing or
divide
Cell Size
Limitations
Most cells are smaller
than the period at the
end of a sentence.
The key factor that
limits cell size is the
ratio of its surface area
to its volume
The larger the
volume the less
efficient the cell
As the cell grows, its
volume increases much
more rapidly than the
surface area.
The larger the
surface Area the
more efficient
the cell
This means the cell
might have difficulty
supplying nutrients and
expelling enough waste
products.
By remaining small, cells
have a higher ratio of
surface area than volume
and can sustain themselves
more easily
Large animals do
not have larger cells,
they have more of
them.
Transport of Substances
Recall that the cell membrane controls cellular
transport…controls what goes into and out of the cell.
Diffusion over large distances is slow and inefficient
because it relies on random movement.
If the distance to travel becomes too large the cell
becomes less efficient
Cells remain small to
maximize the ability of
diffusion and motor
proteins to transport
nutrients and waste
products
Cellular communications
If the cell becomes to large, it becomes
almost impossible for cellular
communications, many of which
involve movement of substances and
signals to various organelles
For example: signals that trigger protein
synthesis might not reach the ribosome
fast enough for protein synthesis to occur
The Cell Cycle
Once a cell reaches its size limit----it
either stops growing or divides
Most cells divide—hence how we replace
old cells with new ones
(RECALL THE CELL THEORY all
cells arise from previously
existing cells)
Cellular reproduction allows you
to grow and heal certain injuries
Interphase
Each time a cell goes through
one complete cycle, it becomes
two cells
G1
Continuous cycles results in
continuous production of new
cells
S
G2
Some cells might complete the cycle in
as few as 8 minutes
Other cells might take up to 1 year
Normal cell cycles take approximately
12-24 hours
G1 Phase
Phase where the cell is growing, carrying out
normal cell functions, and preparing to
replicate DNA
Muscle and nerve cells, exit the cell cycle at
this point and do not divide again
S Phase
Cell copies its DNA in preparation for cell
division
Chromosomes are the structures that contain
the genetic material that is passed from
generation to generation of cells
Chromatin is the relaxed form of DNA in the
cell’s nucleus
G2 Phase
Phase when the cell prepares for the division
of its nucleus.
Microtubules for cell division are synthesized
at this time
The cell also take inventory and makes sure it
is ready to continue with mitosis
Mitosis and Cytokinesis
Phase when cell’s nuclear material divides
and separates into opposite ends of the cell
Cytokinesis is the actual splitting of the
cytoplasm making two daughter cells with
identical nuclei
Prokaryotic
Cell Division
Prokaryotes
which are
bacteria like
cells are much
simpler cells
Prokaryotes
reproduce by a
process called
binary fission