Biology Cells
The Effect of Cell Size on Material Transport
Background
Cells are so small that their existence went unnoticed until the microscope was invented.
The microscope allows scientists to examine the cellular makeup of living organisms for
the first time. A question that arises is: why are cells so small? Is there a factor that limits
the size of a cell? In this lab, you will investigate the possibility that diffusion of nutrients
into the cell may be a limiting factor on cell size.
In this lab, you will work with raw potatoes, cut into cubes to mimic a working model of
a cell. You will cut the potatoes into cubes of pre-determined size and then place the
cubes in a dish containing a food-coloring solution. When the food coloring diffuses into
the potato, it will produce a visible stain. After incubating all potato cubes that are
simulating cells in a food-coloring solution for the same time period, you will slice open
each of them to determine how far the food coloring diffused. By comparing the distance
that the food-coloring diffuses into each size of cell that you make, you will be able to
draw conclusions about whether the rate of material transport may be one of the limiting
factors on cell size.
Question
How does cell size affect the rate of diffusion of materials into a cell?
Materials
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2 raw potatoes.
knife
metric ruler
250 ml beaker (or medium-sized glass/metal kitchen mixing bowl)
1 cup of water
1 teaspoon of food coloring (blue, red, or green)
2 teaspoons of lemon juice
paper towels
cutting board
potato peeler
tweezers
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Safety
Use caution when handling the knife to cut potato cubes. Alert both your teacher and
Learning Coach if you accidentally cut yourself. Wash your hands thoroughly with soap
and warm water before leaving the lab.
Lab Tips
 When handling food coloring, be aware that it will stain surfaces, clothing, and
skin. Avoid using plastic containers while conducting this lab (disposable
containers are okay). Wearing an old T-shirt and plastic gloves may help avoid
any unwanted clothing and skin stains. Wash your hands and any kitchen and lab
tools thoroughly with soap and warm water before leaving the lab.
 Potatoes without their skins will brown after being left out in open air. Do not
peel or cut the potato until you are ready to place the potato cubes into the
solution. If a potato is left out for an extended period of time, carefully trim the
potato so it has a fresh surface.
 If you need to use more than one cup of water to submerge your potatoes, there
should always be one teaspoon of food coloring and two teaspoons of lemon juice
per cup of water.
Example: Two cups of water will require two teaspoons of food coloring and four
teaspoons of lemon juice.
Pre-Lab Work
1. Design an Experiment: What is the independent variable in this experiment (i.e., the
variable that you manipulate)?
2. Measure: How will you determine the size of your cells?
3. Control Variables: Why will you incubate all cells in the same food coloring solution
for the same length of time?
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Procedures
1. Prepare your food coloring solution. Add one cup of water, one teaspoon of food
coloring, and two teaspoons of lemon juice to the 250-ml beaker. Stir the solution
until the food coloring and lemon juice have fully mixed with the water. Tip: It may
be helpful to wear rubber gloves for this step.
2. Rinse the potato with warm water to remove any dirt that may still be present on the
skin. Then pat the potato dry with a paper towel.
3. Carefully remove the skin from the raw potatoes with the potato peeler. Then cut four
potato cubes out of the bodies of the potatoes. Each cube should have the same
length, width, and height. For the first cube, make each side equal to 1 cm. For the
second cube, make each side equal to 2 cm. For the third cube, make each side equal
to 3 cm. For the fourth cube, make each side equal to 4 cm.
4. Carefully place each potato cube into the food coloring solution. Tip: It may be
helpful to wear rubber gloves for this step.
5. Start a timer to allow the potato cubes to incubate undisturbed for 15 minutes. While
the cubes incubate, calculate the surface area, volume, and surface area to volume
ratio for each cube. Enter the values into the data table.
6. At the end of 15 minutes, remove the potato cubes from the food-coloring solution.
Tip: It may be helpful to wear rubber gloves for this step.
7. Place the cubes on the cutting board and carefully slice each down the center.
Measure the distance that the food-coloring solution diffused into each cell.
8. Record your observations in the data table.
Data Table
Cell
Length of
One Side
Surface
Area
Volume
Surface
Area to
Volume
Ratio
1
2
3
4
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Distance
Food
Coloring
Traveled
Analyze and Conclude
Using the information you have gathered, answer the following questions.
1. Compare and Contrast: Summarize your observations of the distance traveled by
the food coloring in the four cells.
2. Analyze Results: Did the cell size affect the extent of diffusion of food coloring
into the cells?
3. Infer: Do the cells have the same surface area to volume ratio? How might the
surface area to volume ratio affect the ability of a cell to take in and use nutrients
from its environment?
4. Apply Concepts: Which cell would be able to supply itself most efficiently with
nutrients diffusing in from the outside—a large cell or a small cell? Why?
© 2014 Connections Education LLC. All rights reserved.