Normal and Plasmolyzed Cells - Polytech High School

Normal and Plasmolyzed Cells

Introduction Diffusion of water molecules across a cell's outer membrane from areas of high water concentration to areas of low water concentration is called osmosis. This movement of water may be harmful to cells. It can result in cell water loss (plasmolysis) when living cells are placed into an environment where the water concentration inside the cell is higher than outside the cell. However, most cells live in an environment where movement of water in and out of the cell is about equal. Therefore, there are no harmful effects to the cell.

Materials Microscope 2 Microscope Slides 2 Cover slips 2 Elodea Leaves (freshwater plant)

Dropper bottle with freshwater Dropper bottle with 6% saltwater solution Tweezers

Procedure 1. To prepare a wet mount of an elodea leaf, put two or three drops of freshwater onto one of the

slides. Place one elodea leaf into the water. Carefully cover it with a cover slip. 2. Prepare a wet mount slide of an elodea leaf in saltwater. Put two to three drops of 6% salt water on a

second slide. Place an elodea leaf in the saltwater and cover it with a cover slip. Be careful not to mix up your freshwater and saltwater slides. Place the saltwater slide aside for at least three minutes while you analyze the freshwater slide. 3. Observe the freshwater slide on high power. 4. In the Data section of this lab draw a picture of at least 4 cells in freshwater. Label the following parts of one of the cell, Chloroplasts, Cell Wall, and Cell Membrane. (You may not be able to see the cell membrane in the freshwater cell ? label where it should be.) 5. In the Data section of this lab draw a picture of at least 4 cells in saltwater. Label the following parts of the cell, Chloroplasts, Cell Wall, and Cell Membrane. (You will be able to see the cell membrane and cell wall distinctly in this cell. If you don't ask for help.) 6. Make sure to note the differences between the cells in fresh and saltwater. It should be obvious. 7. Once you have finished with your observations, wash the slides and put everything back where you found it. Answer the analysis questions in your journal.

Analysis Questions: 1. Define Plasmolysis. (Reread the introduction for the definition.) Read the following statements before answering the questions below (These are the answers to a few of the questions).

Elodea cells normally contain 1% salt and 99% water on the inside Freshwater used in this investigation contains 1% salt and 99% water. Saltwater used in this investigation contains 6% salt and 94% water. Saltwater has a higher concentration of salt then freshwater or Elodea cells. 2. Describe the location of chloroplasts in a normal Elodea cell (in freshwater). 3. Describe the location of chloroplasts in a plasmolyzed cell (in saltwater). 4. (Choose the correct word from each set of parentheses to complete the sentence.) Water will move across the membrane, from (high to low) or (low to high) water concentration. 5. Answer the following questions about the cell in freshwater (see above):

a. What is the percentage of water outside the cell? (Freshwater is outside the cell) b. What is the percentage of water inside the cell? c. How do the percentages compare? d. Did the cell change shape? If no, why do you think there was no change? 6. Answer the following questions about the cell in saltwater (see above): a. What is the percentage of water outside the cell? (Saltwater is outside the cell) b. What is the percentage of water inside the cell? (Before you add saltwater outside) c. Is the percentage of water (concentration) inside the cell, higher or lower than the percentage

outside the cell? d. What happened to the inside of the cell? Describe what you saw and explain why it happened.

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