Download Cell Size Lab

Name _____________________________
AP Biology
Cell Size Lab
(15 points)
Period _________
Date ______________________
Name:_____________________________________________
Period:________ Date:_____________________________
LAB ____. LIMITS TO CELL SIZE
Most
cells areare
between
2 micrometers
and 200
Most cells
between
2 micrometers
and 200 micrometers
micrometers—too
to ofbe
seen Why
withcan’t
naked
eye.
(1 micrometer is 1 small
millionth
a meter).
cells ever
Remember,
a micrometer
is 1
millionth
of a meter!
become larger
than that? Why
don’t
we regularly
find one-Why
can’t
cells
ever become
larger
than
that? Why don’t we
celled
organisms
the size of
frogs or
insects?
regularly find one-celled organisms the size of small
In order for animals,
cells to survive,
they must
multicellular
like frogs
or constantly
even flies? In other
exchange
ions, gases,
and
wastes with
their
words,
why can’t
there nutrients,
ever be an
organism
which
is visible
exchanges
to environment.
the naked eyeThese
and that
is one take
giantplace
cell?at the cell’s
surface—across
the cell membrane. The movement of
In these
ordermaterials
for cells is
to survive,
they mostly
must constantly
accomplished
by diffusionexchange
(flow of
ions,
gases,
nutrients,
and wastes
withacross
their the
environment.
solutes
down
a
concentration
gradient)
cell
These
exchanges
take place
at the
membrane.
Consequently,
factors
that cell’s
affect surface—across
diffusion can
theaffect
cell the
membrane.
The
movement
of these materials is
survival of a cell.
accomplished mostly by diffusion (flow of solutes down a
concentration
gradient)
across
the cell
Consequently,
factors
that affect
One of the core
principles
that govern
the membrane.
efficiency of diffusion
is the ratio
of surface
area diffusion
can
affect
the
survival
of
a
cell.
to volume. Surface area is the amount of cell membrane available for diffusion. So for a cell,
surface
area
actually
represents
how much
diffusion
thatof
can
happen at
Whereas
One
of the
core
principles
that governs
the
efficiency
diffusion
is one
the time.
ratio of
surface area to
volume
is
the
amount
of
cytoplasm
contained
within
the
cell
membrane.
So
for
a
cell,
volume. Surface area is the amount of cell membrane available for diffusion. So for a cell,
volumearea
is how
long It takes
to get from
membrane
to the
the cellatbyone
diffusion.
surface
actually
represents
how the
much
diffusion
thatcenter
can of
happen
time. Whereas
volume is the amount of cytoplasm contained within the cell membrane. So for a cell, volume is
Therefore, to perform diffusion efficiently, there must be an adequate ratio between the
how long It takes to get from the membrane to the center of the cell by diffusion.
cell’s surface area and its volume. But as a sphere (the simplest model of cell shape) gets
larger, its to
volume
increases
at a different
ratethere
than must
its surface
area.
Therefore,
perform
diffusion
efficiently,
be an
adequate ratio between the cell’s
surface area and its volume. But as a sphere (the simplest model of cell shape) gets larger, its
The largest
limitation
cell size rate
is diffusion.
Diffusion
a veryIn
slow
cellinvestigate
were
volume
increases
at aon
different
than its
surfaceisarea.
thisprocess.
lab, weIf awill
this
20
cm
(~8
inches),
it
would
take
days
for
nutrients
to
reach
its
center
or
for
wastes
to
reach
relationship and how it affects diffusion time.
the cell membrane. The cell would quickly starve to death or poison itself with its own
The
primeSolimitation
cell size
theapproaches
limitation its
imposed
by size?
diffusion.
Diffusion
is Ifa very slow
wastes.
what’s thetosolution,
if aiscell
maximum
It’s time
to divide!
process.
If
a
cell
were
20
cm
(~8
inches),
it
would
take
days
for
nutrients
to
reach
cells receive the proper signals, they will divide by mitosis before they become too big. its center or
for wastes to reach the cell membrane. The cell would quickly starve to death or poison itself
with
its own
wastes. So what’s the solution, if a cell approaches its maximum size? It’s time to
PART
1 PROCEDURE
divide! If cells receive the proper signals, they will divide by mitosis before they become too big.
In this lab activity, you will use agar cubes as cell models. You will investigate how
increasing
a cell’s size affects the time for diffusion to move material across the cell. The
PART
1 PROCEDURE
agar for the cubes has been dyed with phenolphthalein—a pH indicator. When the agar
In cubes
this lab
you
will use
agar cubes
as cell
willsodium
investigate
how increasing a
areactivity,
placed in
sodium
hydroxide,
they begin
to models.
turn pinkYou
as the
hydroxide
cell’s
size into
affects
the time
for diffusion
to move process
materialfor
across
the cell.
diffuses
the agar.
You will
time this diffusion
3 different
sizedThe
cellsagar
and for the cubes
has
been
dyed
with
bromothymol
blue—a
pH
indicator.
When
the
agar
cubes
compare them. Diffusion will be considered complete when the clear color completely are placed in
vinegar,
theyfrom
will the
begin
to turn
disappears
center
of theyellow
cell. as the vinegar diffuses into the agar. You will time this
diffusion process for 3 different sized cells and compare them. Diffusion will be considered
complete
whenthe
thesurface
blue color
completely
disappears
the center
of the in
cell.
1. Calculate
area and
volume of
each cube from
and record
your values
Table 1.
Surface area (SA) of a uniform cube = (L x W) x 6
Volume (V) of a cube = L x W x H
2. Fill in the surface area to volume ratios for each cube in Table 1.
Surface are to volume ratio (SA:V) = SA/V
1 of 4
Developed by Kim B. Foglia • www.ExploreBiology.com • ã2010
Table 1: Cell Dimensions and Time for Diffusion in Various Sized Cubes
Surface Area
Cell Size (cm)
Volume (cm3)
SA:V Ratio
(cm2)
Time (min)
1x1x1
2x2x2
PART 2 PROCEDURE
1. Now that you have observed differences in the rate of diffusion, calculate the surface
area and volume for the cube in Table 2.
2. Determine the surface area to volume ratio.
3. How do you predict the rate of diffusion will compare for this cube? Do you think it
will be similar to the 1x1x1 or the 2x2x2? Explain your reasoning.
Prediction:
_________________________________________________________________________________________________________
_________________________________________________________________________________________________________
_________________________________________________________________________________________________________
_________________________________________________________________________________________________________
_________________________________________________________________________________________________________
_________________________________________________________________________________________________________
_________________________________________________________________________________________________________
Table 2: Cell Dimensions and Time for Diffusion in a 1x1x8 cube
Surface Area
Cell Size (cm)
Volume (cm3)
SA:V Ratio
(cm2)
Time (min)
1x1x8
Post Lab Questions
Complete the following questions on a separate piece of paper and attach to this lab.
1. The 2x2x2 cell and the 1x1x8 cell have the same volume. Were their diffusion times
the same? Explain why or why not.
2. In general, what is the relationship between the SA:V ratio and diffusion time?
3. Explain why cells can’t get very, very big.
4. Each of the following types of cells are shaped very differently than the classical
round or boxy shape that you see drawn in introductory textbook chapters on cells.
For each of the following cells, draw a diagram for and explain how the unique shape
is tied to the function that each performs.
 Erythrocytes (red blood cells)
 Simple columnar epithelial cells (with microvilli) lining small intestine
 Root hairs in plants