Page 1 – Demonstrating Osmosis in Carrot Tissue
Demonstrating Osmosis in Carrot Tissue
Background
Osmosis is the diffusion of water through a semipermeable
membrane. The cell membranes of carrots exhibit this selective
permeability. These membranes allow water and small nonpolar
molecules to pass freely into and out of the cells of the carrot according
to the surrounding concentration gradient.
As you have already learned, water moves from areas of low solute
concentration (high water concentration) to areas of high solute concentration (low water
concentration.) Therefore, if carrot cells are placed in a solution with a higher or lower solute
concentration, then water will move across the cell membranes of the carrot cells until the cells
and the solution have reached equilibrium. Water will move at different rates depending upon
the strength of the concentration gradient that exists between the carrot cells and the solution.
The stronger the gradient, the faster the water will move.
In this laboratory, you will explore how the concentrations of various solutions cause carrot
cells to either take up or lose water. You will be placing carrot slices in each of the following
four solutions: pure water, and 1%, 2%, and 3% NaCl (salt) solutions. After a short period of
time you will compare the mass of the carrot slices to their original mass to determine if the
carrots either gained or lost water through osmosis. At the conclusion of this laboratory you
will analyze your data to estimate the solute concentration of carrot tissue.
Objectives
In this experiment, you will
 Understand how the concentration gradient between cells and their environment can
cause water to move by osmosis.
 Use an electronic balance to calculate the percent weight gain or loss of carrots placed in a
solution of known tonicity (strength).
 Determine which solution concentration(s) will cause carrot cells to gain water? Lose
water?
 Analyze percent weight gain/loss data to estimate the solute concentration of carrot tissue.
Pre-Lab Questions
1. What is osmosis?
2. What is a concentration gradient? How does the concentration gradient affect the rate at
which osmosis occurs?
3. In which solutions do you think the carrot cells would gain water by osmosis? What
term would you use to describe these solutions?
4. In which solutions do you think the carrot cells would lose water by osmosis? What
term would you use to describe these solutions?
5. What solute concentration do you think will be isotonic to carrot tissue?
Page 2 – Demonstrating Osmosis in Carrot Tissue
Lab Report Hint: Using your answers from Pre-Lab questions 3-5, create a hypothesis about what will
happen to the carrot cells in each of the four solutions.
Materials
Each group will need the following:
raw carrot
electronic balance
blade or knife
4 petri dishes
distilled water
grease pencil
1%, 2%, and 3% NaCl solutions
paper towels
calculator
Safety
Because of the use of sodium chloride solutions, goggles and lab aprons should be worn at ALL times.
Students will also be using blades to slice carrots. Care should be taken to avoid cutting fingers or other
body parts. Use caution when handling glassware as it can break easily and cut you.
Procedure
1. Using the blade, carefully slice the carrot into discs. You will need 20 discs that are 2-3 mm
thick. Be careful to cut away from you and keep fingers out of the way of the blade.
2. Place a paper towel on the weighing dish of the electronic balance and tare the balance.
3. Place 5 carrot discs on the paper towel and weigh them as a group. Record the weight of
these discs in the table provided under “mass at start.” Spread the five discs flat in a single
layer in a petri dish.
4. Repeat steps 2-3 for the remaining carrot discs.
5. Label one petri dish “0% NaCl.” Label the remaining dishes “1% NaCl,” “2% NaCl,” and
“3% NaCl.” This refers to the percentage of NaCl (sodium chloride or “salt”) by weight that
is present in each solution.
6. Fill the petri dish labeled 0% NaCl with enough distilled water to just cover the carrot slices.
7. Fill the other petri dishes accordingly with the sodium chloride solution that corresponds to
their label. Set all petri dishes aside.
Allow the carrot slices to soak in the solutions for at least 15 minutes, and then proceed to the next step.
8. Drain the liquid from each petri dish into the sink. Gently blot the carrot discs with a paper
towel. Be careful to not mix them up.
9. Re-tare the balance and re-weigh each set of discs. Record the result under “mass at end” in
the data table.
10. Feel the texture of your carrot slices. Note your observations and any differences between
groups of slices in the data table.
11. Discard the carrots in the garbage. Rinse and dry the petri dishes and leave them on a paper
towel at your station.
Page 3 – Demonstrating Osmosis in Carrot Tissue
12. Using a calculator, find the percent weight change for each group of carrots. This can be
determined by using the following formula:
(mass at end - mass at start)
x 100 = percent weight change
mass at start
Record these percentages in your data table.
13. Collect the percent weight change values of other lab groups and find the mean (average)
weight change for each solution. Record this in your data table.
Data Table
SOLUTIONS
0% NaCl
Strength
Pure water
Mass at start
(g)
Mass at
end (g)
Texture
(soft or firm)
Percent
Weight
Change (%)
Percent Weight
Change (%) of
other groups
Mean
(Average)
Weight Change
(%)
Tonicity of
Solution
(compared to
carrot cells)
1% NaCl
2% NaCl
3% NaCl
(increasingly stronger salt (NaCl) solutions)
Page 4 – Demonstrating Osmosis in Carrot Tissue
Post-Lab Questions:
1.) Why use carrot slices instead of large chunks of carrot?
2.) Why is it important to use the percent weight change when determining the effects of
osmosis? Why not just evaluate the change in weight?
3.) What does it mean if the percent weight change is a negative number?
4.) Create a line graph of solution concentration vs. mean (average) weight change of carrot
slices. Your graph should meet the following requirements:

It should be done on graph paper or using a spreadsheet program (such as Microsoft Excel).

The independent variable (solution concentration) should be on the x-axis. Spread the values
evenly along the axis and include the proper units in the axis label.

The dependent variable (mean weight change) should be included on the y-axis. Space these
values appropriately along the axis and include the proper units in the axis label. Note: This
axis may need to extend both above and below the x-axis to fit negative values.

Include an appropriate title for your graph.

A line of “best fit” plotted through your data points.

The graph should be included in the “Analysis” section of your laboratory report.
5.) Based on your results, what might be the concentration of solutes in the cytoplasm of the
carrot cells at the start of this experiment?
6.) What do you think will happen to the carrot slices if you leave them in the solutions
overnight?
7.) What can you say about the reliability of this experiment? Hint: How close were other
group’s results to yours?
8.) Explain any inconsistencies in your data. Could an error on the part of a lab group have
resulted in these inconsistencies? If so, how?
Lab Report Hint: Use your answers from the Post-lab questions above to write your Analysis section.
References:
Pupil’s experiments with osmosis in carrot tissue. Retrieved on November 18, 2002 from
<http://www.biotopics.co.uk/life/carrot.html>