Download Why Are Cells So Small?

Why Are Cells So Small?
Cells Have Limits In Size
● Most cells in
living things are
the same size
● There are problems
if a cell is too
small or too large
If A Cell Was Too Small
● It couldn’t contain
all the organelles
and nutrients
necessary for
survival
If A Cell Was Too Big
● The cell couldn’t get enough H2O,
nutrients, and O2 into the cell to live
● The cell couldn’t remove all its waste
● DNA couldn’t make enough proteins to
support the cell
● Too much energy and time would be used to
move things across the cell
If A Cell Was Too Big
Surface Area/Volume Ratio
● SA/V ratio determines the
upper limit of cell size
● Surface area- the total
area of the outer surface
of an object
● Volume- the amount of space
an object takes up
Surface Area/Volume Ratio
● Surface area formula for a
cube= length x width x # of
sides
● Volume formula for a cube=
length x width x height
Surface Area/Volume Ratio
● If length, width, and
height of cube is 1mm...
○ SA= 1mm x 1mm x 6 =
○ V= 1mm x 1mm x 1mm =
● SA/V ratio=
Surface Area/Volume Ratio
● If length, width, and
height of cube is 2mm...
○ SA= 2mm x 2mm x 6 =
○ V= 2mm x 2mm x 2mm =
● SA/V ratio=
Surface Area/Volume Ratio
● If length, width, and
height of cube is 3mm...
○ SA= 3mm x 3mm x 6 =
○ V= 3mm x 3mm x 3mm =
● SA/V ratio=
Surface Area/Volume Ratio
● The larger the cell, the smaller the SA/V
ratio
● The smaller the ratio, the less efficient
the cell
○ The cell membrane is too small to take
in enough nutrients for the large volume
Getting Around The SA/V Ratio
● A cell can be flat and thin instead of
cube-like
○ A cell can have the same volume but a
bigger surface area
○ ex. neurons
Getting Around The SA/V Ratio
● A
○
○
○
2mmx2mmx2mm cube ● A 1mmx1mmx8mm polygon
SA=2mmx2mmx6=
○ SA=4(1mmx8mm)+2
V=2mmx2mmx2mm=
(1mmx1mm)=
SA/V=
○ V=1mmx1mmx28mm=
○ SA/V=
Getting Around The SA/V Ratio
● A cell can increase surface area by having
folds in the cell membrane
○ increases exposure to environment
○ ex. intestine cells