Download Cell Size

Why are cells so small?
Why cells are
small?

•
Diffusion limits
cell size
•
DNA limits the
cell size.
•
Surface areavolume ratio


Diffusion is fast and
efficient over short
distances
Diffusion becomes slow
and inefficient over
larger distances.
• Small cell

good diffusion
• Big cell

bad diffusion

Speed of Diffusion
• An organelle in the
center of a 20 μm
diameter cell receives
supplies a fraction of a
second after it enters
the cell.
• An organelle in the
center of a 20 cm
diameter cell would
have to wait months
before receiving
supplies that enter the
cell.



The DNA tells the cell
which proteins to be
made.
Not enough protein
the cell will die. Takes
time for protein to be
produced.
As cells increase in
size, no extra DNA is
made



As cell size increases,
volume increases much
faster than surface
area.
A bigger cell has a
smaller surface area to
volume ratio
This smaller ratio does
not allow the cell to get
enough “things” into it



Before a cell gets too
large, it divides into
two “daughter” cells.
Before cell division
takes place, the cell
must replicate all of
its DNA.
The cell then divides
and solves the problem
of the cell becoming
too large.
1.
2.
3.
4.
Cell size vs. surface area must remain
at an efficient ratio
Growth - bigger organism needs more
cells
Repair - regeneration of skin, blood &
bone etc.
Reproduction - asexual vs sexual
 Cut
out and make boxes (cells)
 Calculate area of one side ( L X W)
 Calculate total surface area (L X W X # of sides)
 Calculate
 Measure
volume of cube (L X W X H)
distance from edge to the middle of
the cell
 Calculate
surface area to volume ratio (SA/V)