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Name: _________________________________
Date: ____________ Period: _____________
OSMOSIS Lab: Plasmolysis and Reverse Plasmolysis
Discussion:
Substances dissolved in water move across the cell membrane by a process called diffusion.
This involves the movement of a substance where there is a large concentration to where there is a
small concentration. Diffusion of water molecules across the cell membrane is called osmosis. This
movement may be harmful to cells. If too much water leaves a cell, the cell membrane pulls away
from the cell wall and it pulls the cell contents with it. This is called plasmolysis. Plasmolysis can
kill a cell. Most cells live in an environment where the movement of water in and out of the cell is
equal.
A scientist can observe the effects of water loss by observing the shrinking of a cell’s
cytoplasm with a microscope. This observation is a qualitative measurement. In measuring the
amount of water loss in grams, a scientist makes a quantitative measurement.
Since only water and not salt can pass through a potato’s membrane, predict what would
happen if a piece of potato was placed in three different salt solutions; 0%, 10%, and 25%.
Objectives: Students will be able to
1. observe the qualitative effects of plasmolysis and reverse plasmolysis in Elodea cells.
2. quantitatively measure the rate of plasmolysis in potato slices.
Materials:
white potatoes, beakers, balance, paper towel, labels, distilled water (100% pure water), different
concentrations of salt (NaCl) solutions, Elodea, microscope, glass slide, cover slip, dropper
Procedure:
Part A:
1. Cut 3 pieces of potato approximately 1 cubic cm each. Determine the mass (g) of each potato cube
and record.
2. Place 1 cube in each of the beakers labeled A, B, and C. Add the following solutions to the
respective beakers and let the potatoes soak for 30 minutes.
A = pure water
B = 10% NaCl
C = 25%+ NaCl
3. After 30 minutes remove the potato cubes from the beakers. Wipe off the excess solution by
blotting the cubes with a paper towel and determine the mass (g) of each. Calculate the percent
change by using the formula below and record your results in the data table.
amount of increase or decrease
mass before soaking
X 100 = % change
Part B:
1. Prepare a wet mount of an Elodea leaf. Observe a leaf under high power. Draw a diagram of 1 or
2 Elodea cells and label the cell wall, chloroplasts, and central vacuole.
3. Add a drop of salt solution along one edge of the cover slip. Place a piece of absorbent paper along
the opposite edge of the cover slip. (The paper towel will absorb the tap water and draw in the salt
solution).
4. Observe the leave under high power. Find and draw a plasmolyzed cell. Label the cell wall,
chloroplasts, and cell membrane.
5. Add a drop of distilled water (100% pure water) to the slide using the same procedure as described
in #3. Observe the cells. Record your observations.
Name: ___________________________________________
Date: _________ Period: ______
Data Sheet: Plasmolysis and Reverse Plasmolysis
TITLE: ___________________________________________________________________________
PURPOSE: (summarize objectives): The purpose of this lab is to ____________________________
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MATERIALS: The following materials were used during this lab: ___________________________
__________________________________________________________________________________
HYPOTHESIS: (Use the italicized information in the background to write your hypothesis):
________________________________________________________________________________
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PROCEDURE: (summarize the procedure in your own words):
PART A: _________________________________________________________________
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PART B: _________________________________________________________________
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Pre-Lab Questions: Define the following terms:
Isotonic: ___________________________________________________________________________
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Hypertonic: ________________________________________________________________________
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Hypotonic: ________________________________________________________________________
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Turgor pressure: ____________________________________________________________________
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Plasmolysis: _______________________________________________________________________
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DATA: (Complete after Part B)
Part A:
Example
Mass
Before
Mass
After
Difference
Percent
Change
Beaker A
3.6g
9.8 g
4.8g
6.0 g
+ 1.2g
Beaker B
Beaker C
- 3.8 g
(1.2 g / 3.6 g) = 33%
(3.8 g / 9.8 g) = -39%
** HINT: Use correct units and signs to show weight gain (+) or weight loss (-) when necessary!
Analysis Questions
1. Which potato cube gained the most mass after soaking? Explain why using the terms above. ____
__________________________________________________________________________________
__________________________________________________________________________________
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2. Which potato lost the most mass after soaking? Explain why using the terms above. ___________
__________________________________________________________________________________
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Part B:
Normal Elodea Cell
Total Mag: _______
Plasmolyzed Elodea Cell
Total Mag:_____
1. Was the salt water solution you added isotonic, hypertonic, or hypotonic compared to the cell?
Why? _____________________________________________________________________________
__________________________________________________________________________________
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Turgid Cell
Total Mag: _____
2. After adding distilled water to the plasymolyzed cell what did you observe? __________________
__________________________________________________________________________________
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3. Was the distilled water that you added to the plasmolyzed Elodea cell isotonic, hypertonic, or
hypotonic compared to the cell? Why? __________________________________________________
__________________________________________________________________________________
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3. What caused reverse plasmolysis? ___________________________________________________
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CONCLUSION:
The purpose of this lab was to ____________________________________________________
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My hypothesis stated that _______________________________________________________
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My hypothesis was ___________________________ because (provide evidence or data from
(supported / rejected)
your lab):
_________________________________________________________________________
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CRITICAL THINKING:
6. When a patient needs fluids, nurses administer a saline solution that is isotonic to the patient’s
body. a) Why is this so important? _____________________________________________________
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b) What would happen if the administered solution was hypertonic or hypotonic? ________________
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