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Plasmolysis
Plasmolysis
Comparing Elodea and Onion Cell Plasmolysis
INTRODUCTION
Have you ever seen a plant with wilted leaves? Plant leaves wilt in response to a loss of water from
individual cells. When the cells lose too much water, the cell membrane will shrink away from the cell
wall in a process called plasmolysis. The leaf appears wilted because the individual cells are flaccid,
meaning that their central vacuole is no longer filled with water. In a healthy plant cell, the large central
vacuole is filled with water creating an internal pressure, or turgor pressure, which helps keep the cell
membrane pressed against the cell wall. A plant cell with a water filled central vacuole will be stiff or
turgid See Figure 1. A plant cell whose central vacuole is not filled will have a lower internal turgor
pressure and will be flaccid See Figure 1.
Large central
vacuole
Cell membrane separating
from the cell wall
Cell wall
Turgid
Vacuole
begins
losing water
Flaccid
Fig. 1
Water moves across the plasma membrane by osmosis from an area of high water concentration to an
area with lower water concentration. This movement of water effects cell homeostasis. Plant cells are
homeostatic when the central vacuole is filled with water. Plant cells placed in hypotonic solutions tend
to exhibit turgidity while plant cells in hypertonic solutions will lose water and become flaccid. Bacteria
and fungus, which also have cell walls, will also experience plasmolysis in hypertonic solutions.
Plasomlysis can be observed in the laboratory by surrounding plant cells with hypertonic and hypotonic
solutions and observing the effects on the cell.
PURPOSE
In this lab activity, you will expose onion and Elodea cells to a solution of salt to observe plasmolysis.
MATERIALS
10% salt solution
red onion epidermal cells
dropper
paper towel
distilled water
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2 slides
2 coverslips
microscope
forceps
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Safety Alert
1. Handle and carry microscope properly.
2. When focusing the microscope on high power, use the fine adjustment knob to avoid
breaking the slide.
3. Onion and onion juice may be an irritant to the eye. Avoid contact with the eye.
PROCEDURE
1. Read the introduction section of the lab.
2. Formulate a hypothesis explaining what you think will happen when onion cells are placed in a 10%
salt solution. Write your hypothesis on the student answer page.
3. Using forceps, remove a small segment of epidermis from a piece of red onion. Prepare a wet mount
slide by adding the onion epidermis to a drop of tap water placed in the center of a clean glass slide.
Cover with a cover slip
4. Focus the slide under low power and then switch to high power. Adjust the microscope’s diaphragm
to the amount of light that allows you to visualize the cell wall and the vacuole of the cell. Make a
labeled sketch of your observations in the space provided on the student answer page.
5. Leaving the slide on the microscope stage, place a drop of 10% salt solution on the left hand side of
the slide. The drop should touch the side of the coverslip. Place a small piece of paper towel on the
right hand side of the slide to draw the salt water across the slide See Figure 2. This will expose the
onion epidermis to the hypertonic salt solution.
Movement of salt solution
Drop of
salt water
coverslip
Drop of
salt water
Piece of
paper towel
coverslip
Piece of
paper towel
Fig. 2
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Plasmolysis
6. Observe the effects of the salt solution on the onion cells. You may notice the movement of
particles in the water as the water is wicked to the opposite side of the slide. Do not let these
particles distract your attention. Focus on what occurs inside the onion cells. Notice any changes in
color, size, or shape of the cell structures. Make a labeled sketch of your observations in the space
provided on the student answer page.
7. Flood the onion cells with a hypotonic solution by placing a drop of distilled on the left hand side of
the slide. The drop should touch the edge of the coverslip. Place a small piece of paper towel on the
right hand side of the slide to draw the distilled water across the slide.
8. Observe the effects of the distilled water on the onion cells. Make a labeled sketch of your
observations in the space provided on the student answer page.
9. Formulate a hypothesis explaining what you think will happen when Elodea cells are placed in a
10% salt solution. Write your hypothesis on the student answer page.
10. Repeat steps 3 through 6 using the cells found in one leaf of Elodea instead of onion cells.
11. Flood the Elodea cells with a hypotonic solution by placing a drop of distilled on the left hand side
of the slide. The drop should touch the edge of the coverslip. Place a small piece of paper towel on
the right hand side of the slide to draw the distilled water across the slide.
12. Observe the effects of the distilled water on the Elodea cells. Make a labeled sketch of your
observations in the space provided on the student answer page.
13. Remove the slide from the stage of the microscope, clean all slides and coverslips. Store your
microscope as instructed by your teacher.
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Plasmolysis
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Name _____________________________________
Period _____________________________________
Plasmolysis
Comparing Elodea and Onion Cell Plasmolysis
HYPOTHESIS # 1
HYPOTHESIS #2
DATA AND OBSERVATIONS
Onion Cells: Tap water
Elodea Cells: Tap water
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Onion Cells: 10% salt solution
Onion Cells: Distilled Water
Elodea Cells: 10% salt solution
Elodea Cells: Distilled water
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ANALYSIS
1. Describe the effects of placing an onion cell in a hypertonic solution.
2. Explain what happened to the Elodea cells when they were exposed to distilled water.
3. In which solution were the onion cells most turgid?
4. In which solution were the Elodea cells most turgid?
CONCLUSION QUESTIONS
1. How do onion and Elodea cells compare in their response to being placed in a 10% salt solution?
2. If a human blood cell is placed in distilled water, it will eventually rupture and go through lysis.
Why did the onion and Elodea cells not rupture when placed in distilled water?
3. Predict what would happen if cells of yeast, a fungus, had been used in this experiment.
4. After a family picnic, Sharlonda dumped the ice and rock salt from the ice cream maker in the back
yard. That area of the yard now contains dead, brown grass. Explain why this happened. Use the
words hypotonic, hypertonic and plasmolysis in your explanation.
5. Using your understanding of plasmolysis and osmosis, explain why grocery stores frequently spray
the produce and vegetables with a fine mist of water.
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