Download osmosis-in-plant-cells-plasmolysis-of-elodea-lab

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Date ______________________
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Osmosis in Plant Cells
Plasmolysis of Elodea
Introduction:
All eukaryotic cells have an elaborate system of membranes that enclose the cell and create internal compartments
that allow a huge variety of processes to occur within the cytoplasm. This membrane is composed of a hydrophilic
lipid bilayer and proteins. The plasma membrane both isolates the cell and allows selective interactions between the
cell and its environment. One way in which the membrane helps the cell interact with its environment is through
diffusion. Diffusion is defined as the random movement of molecules. When no barriers are present, the molecules
are evenly distributed by diffusion. A cell membrane is considered a type of barrier to diffusion. When a cell
membrane is present, diffusion is classified as simple or facilitated. In simple diffusion, the molecule is able to pass
freely in and out of the cell through small pores in the membrane. Facilitated diffusion requires carrier proteins
that can assist molecules across the membrane.
The ability of water to pass through cell membranes is also called osmosis. Under different environmental
conditions, osmosis can affect the shape of a cell. For example, blood cells are normally found in plasma, a solution
containing numerous salts. If water is added to the cells, the water enters the cells through osmosis causing them to
swell and even burst. Likewise, if the cells are placed
in a solution containing more salts than plasma, water
moves out of the cell and the cell shrivels and shrinks.
This process is slightly different in plant cells because
of the presence of a cell wall. With the addition of
water, the cell body expands, but retains its shape,
supported by the stiff cell wall, as shown in Figure 1.
Under conditions where water is removed from the
cell, the cell wall maintains its shape, but the cell
membrane pulls away from the cell wall and the cell body is reduced in size. This shrinking of the cell body is called
plasmolysis.
Purpose
The purpose of this lab is to observe the effect of a hypertonic and hypotonic osmotic environment on a plant cell.
The process of cell shrinkage due to a hypertonic environment is knows as plasmolysis.
Question: What salt solution will cause plasmolysis in the Elodea leaf?
Hypothesis:
Materials:
Elodea leaves
Distilled water
Various salt-water concentrations
Slides
Coverslips
Microscope
Micropipettes
Forceps
Beakers
Part 1. Elodea leaf in distilled water
Procedure:
1. Use forceps to obtain a single leaf of the Elodea plant and place on a slide.
2. Use a micropipette, place one or two drops of distilled water onto the leaf so it is covered.
3. Prepare a wet mount slide, as shown in Figure 2.
4.
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Using the lowest power objective (4X) and the coarse adjustment knob, bring your specimen into focus.
Change to the next objective lens and using the fine adjustment knob, bring your specimen into focus.
Draw one cell of the Elodea leaf.
Would you describe the Elodea leaf as isotonic, hypertonic, or hypotonic?
Total magnification _______
Part 2. Plasmolysis with 10% salt solution
Procedure:
1. Using the same slide, do not remove the coverslip; add several drops of the 10% salt solution with a
micropipette to one side of the coverslip.
2. Place the edge of a paper towel gently against the coverslip opposite the salt solution, as shown below. This will
wick the salt solution completely under the coverslip without disturbing the slide preparation.
3.
4.
5.
6.
7.
Wait approximately 3-4 minutes.
Using the lowest power objective (4X) and the coarse adjustment knob, bring your specimen into focus.
Change to the next objective lens and using the fine adjustment knob, bring your specimen into focus.
Draw one cell of the Elodea leaf.
Would you describe the Elodea leaf as isotonic, hypertonic, or hypotonic?
Total magnification _______
Part 3. Various salt solutions and plasmolysis
Procedure
1. Use forceps to obtain 2 single leaves of the Elodea plant and place on 2 separate slides.
2. Choose one salt solutions 2%, 4%, 6%, or 8% and use a micropipette to place 2 to 3 drops on an Elodea leaf.
Place coverslip on leaf.
3. Choose another salt solutions 2%, 4%, 6%, or 8% and use a micropipette to place 2 to 3 drops on an Elodea
leaf. Place coverslip on leaf.
4. Wait approximately 3-4 minutes.
5. Using the lowest power objective (4X) and the coarse adjustment knob, bring your specimen into focus.
6. Change to the next objective lens and using the fine adjustment knob, bring your specimen into focus.
7. Draw one cell of the Elodea leaf for each salt solution.
________ Salt solution
________ Salt solution
Total magnification ________
Total magnification ________
Observations
Results/Data
Using the table below, determine whether or not plasmolysis occurred with each salt solution.
NOTE: You will have to obtain other groups data since you only selected two solutions.
Salt Solution concentration
No salt solution (negative control)
10% salt solution (positive control)
2% salt solution
4% salt solution
6% salt solution
8% salt solution
Did plasmolysis occur? Y/N
Analysis
Explain the data you collected in words. First set the stage by giving a general description of the
chart. Next, describe the specific data in the chart, include specific data that shows at what solution
plasmolysis occurred. Observations are NOT included in the analysis; only data.
Conclusion
In your own words and in complete sentences summarize your experiment from start to finish. Begin
by explaining the purpose of the experiment. Restate your hypothesis and give reasons why you made
the prediction you did. Indicate if your hypothesis was correct or incorrect. Use the information from
the data in your lab to support your conclusion. If your hypothesis was incorrect, give possible reasons
why. You should also address anything that might have had an impact on your results, and suggest
ways that you might be able to make the experiment better. (i.e. better control over variables,
experimental conditions, etc.) This should be at least 4 sentences or more.