Introduction
Plant cells have several structures that animal cells do not. These structures are
important for several plant functions, including photosynthesis. Chloroplasts contain
pigments that are used in the conversion of light energy into stored energy, large
vacuoles hold water which is essential for photosynthesis, and the cell wall allows a
plant cell to maintain pressure and solute potential. This lab will introduce you to the
effects of changes in water potential on plant cells. When water leaves the vacuole of a
plant cell, the cytoplasm pulls away from the cell wall. If the vacuole is full, the
cytoplasm puts pressure on the cell wall. We call this turgor.
Procedure
Elodea cells in tap water
1. Prepare a wet mount of an Elodea leaf on a slide using tap water.
2. Observe the leaf at 40X and 100X.
3. Draw the plant cells and record your observations in your notebook.
Elodea cells in salt water
4. Remove the slide from the stage.
5. Place 2 drops of the 10% salt solution on the slide at the left edge of the cover
slip.
6. Tear off a small piece of paper towel and place the torn edge on the slide at the
right edge of the cover slip. The piece of towel should begin to soak up water,
drawing the salt solution under the cover slip as it does so. (See Figure)
7. Return the slide to the microscope stage and observe the cells at 40X and 100X.
8. Draw the plant cells and record your observations in your notebook.
Plant Cell Plasmolysis
Elodea cells in distilled water
9. To increase the turgor pressure in your Elodea cells, we can use distilled water.
Repeat steps 4-6 using distilled water.
10. Quickly replace the slide and try to observe the cells as their vacuole is refilling.
11. Draw the plant cells and record your observations in your notebook.
Questions
1. What happens to the cells as the salt water flows under the coverslip?
2. Is the salt water solution hypo-osmotic or hyperosmotic? Explain.
3. Is this an example of passive or active transport? Explain.
4. Explain why it is important that a plant cell have a cell wall (other than support of
the plant itself)? What might happen to an animal cell placed in distilled water?
5. Describe the following:
a. simple diffusion
b. facilitated diffusion
c. osmosis
6. How are size and charge of molecules related to their movement across the cell
membrane?
7. What are the steps of active transport?
8. Describe endo- and exocytosis.