Download DATA AND OBSERVATIONS: Draw all of the cells that you see

Name: ____________________________________________Date:______________________Period:______
Plasmolysis of Plant Cells: Pre-lab Activity
Read over the “Plasmolysis of Plant Cells”. Answer the following questions in order to prepare for your lab.
1. In your own words, describe plasmolysis.
2. When does plasmolysis occur?
3. In the box to the right, draw a picture of a plant cell
that has been plasmolysized. Make sure to label
the following: location of fresh H2O, Cell membrane,
cell wall.
4. Define osmosis.
5. List the three objectives of this lab.
6. What is added to the Elodea leaf and red onion skin that causes plasmolysis to occur?
7. Why does the water leave the cells?
8. How will you know if plasmolysis occurred?
Elodea Cells before plasmolysis
Elodea Cells after plasmolysis
Cell
Membrane
Plasmolysis of Plant Cells
What is plasmolysis?
Plasmolysis occurs when a plant cell membrane shrinks away from its cell wall. This occurs when water
moves out of the plant cell.
Notice the cell membrane of the plant cell
pulling away from the cell wall. Label cell wall & cell membrane in the
picture.
This occurs when the cell loses water.
Background: Diffusion of water across a cell’s membrane is called osmosis. This movement of water may be harmful to
cells. If too much water is lost from the cell, the cell membrane and the cell contents shrink away from the cell wall. This,
remember, is called plasmolysis.
Objectives:
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Prepare a wet-mount slide of Elodea (plant) leaf and red onion skin cells.
Observe plasmolysis (pulling away of cell membrane from the cell wall) in the cell as salt water is added.
Materials:
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microscope
1 slide
1 cover slip
paper towel
foreceps
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Elodea leaf (freshwater plant)
disposable pipettes
salt water
fresh water
Procedure:
_____ 1. Make a wet-mount slide of an Elodea leaf as described below:
- obtain a glass slide
- using forceps, place one Elodea leaf in the center of the slide
- using a pipette, place one or two drops of fresh water on the Elodea leaf
- carefully cover the leaf with a coverslip
_____ 2. Place the slide on the stage of the microscope.
_____ 3. Observe the leaf under low, medium, and high powers. Note the location of the chloroplasts in relation to the cell
wall.
_____ 4. Draw the normal cells in fresh water in the space provided in the Data and Observation section of this lab. Draw
what you see under the microscope. Label the cell wall, cell membrane, and chloroplasts.
_____ 5. Using a pipette, add two to three drops of salt water along the
edge of the coverslip. Place a piece of paper towel along
the opposite edge of the coverslip. The fresh water will
soak into the paper towel, pulling the salt water over the
leaf (see Figure 1).
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Figure 1
_____ 6. Again note the location of the chloroplasts in relation to the cell wall. (If the membrane and the cell contents have
pulled away from the cell wall, this is plasmolysis.)
_____ 7. Draw the plasmolyzed cells in the space provided in the Data and Observation section of this lab. Label the cell
wall, cell membrane, and chloroplasts.
_____ 8. Add two drops of fresh water to the slide, following the procedure in step 5. Observe the cells under the
microscope.
_____ 9. Repeat the above procedure with red onion skin cells. Take a small piece of onion and peel off a sheet of the purple
skin. The purple pigment is concentrated in the top layer. It is not easy to peel off a THIN red onion skin. Too
thick and the osmotic action will not be observed because too many cells crowd the slide—layer upon layer. A thin
skin curls up on itself and must be placed flat against the slide—and again, too many cell layers will impede the
osmotic observation. Be careful flattening the skin so that you do not rupture the cells in the process and lose the
purple pigment. Record your observation below.
Data and Observations: Draw all of the cells that you see under the microscope in the circles below. In the first circle, draw
the Elodea cells in tap water. Label the cell wall and the chloroplast. In the second circle, draw the Elodea cells in salt water.
Label the cell wall, cell membrane, and chloroplast. In the third circle, draw the red onion skin cells in water. Label the cell
wall and cytoplasm. In the fourth circle, draw the red onion cells in salt water. Label the cytoplasm, cell wall, and membrane.
Elodea cells in tap water.
Red onion skin cells in tap water.
Elodea cells in salt water.
Red onion skin cells in salt water.
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Analysis: Answer the following questions in complete sentences.
1. Describe the location of the chloroplasts in an Elodea cell in tap water.
2. Describe the location of chloroplasts in an Elodea cell after salt water was added to the slide.
3. Which direction did water move when the salt solution was added to the slides?
4. Why didn’t the cell walls collapse?
5. What process allowed the water to move across the cell membrane?
6. If pure water was added to the plasmolyzed cells, what would happen?
7. Use the term turgor pressure to explain why grocery store owners spray fresh fruits and vegetables with water.
8. Will a cell swell or shrink in a hypotonic solution?
9. Was the salt water solution hypertonic or hypotonic compared to the cell?
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