What is the Effect of a Salt Solution on Green Plant Cells?

Purpose:

Students will be able to:

·  Describe the effect of a salt solution on green plant cells

·  Identify and label the vacuole, chloroplast, cytoplasm, cell membrane, and cell wall of a green plant cell

·  Describe the effects of plasmolysis of green plant cells

Materials:

forceps slide dropper

light microscope cover slip distilled water solution

Elodea 10% salt solution

Procedure:

1.  With forceps, remove a single young leaf, mount it on a slide in a drop of distilled water, and cover with a coverslip.

2.  Examine the leaf first with the low power objective. Now switch to the high power objective. Observe the abundance of green bodies in the cytoplasm. These are the chloroplasts, organelles that function in photosynthesis and are typical of a green plant.

3.  Find the cell wall, a structure distinguishing plant from animal cells, visible as a clear area surrounding the cytoplasm.

4.  After the cells have warmed up a bit, notice the cytoplasmic streaming taking place. Movement of the chloroplasts along the cell wall is the most obvious visual evidence of cytoplasmic streaming.

5.  Remember you are looking at a three-dimensional object. In the middle of the cell is a large, clear central vacuole, which can take up from 50% to 90% of the cell interior. Because the vacuole in Elodea is transparent, it cannot be seen with the light microscope.

6.  Next locate the nucleus within the cytoplasm. It will appear as a clear or slightly amber body that is slightly larger than the chloroplast.

7.  On a separate sheet of paper draw a few cells of Elodea. Label the vacuole, chloroplast, cytoplasm, and cell wall.

8.  Remove the slide from the microscope.

9.  Using a dropper, add a drop (or two) of 10% salt solution to the Elodea. Wait 3 minutes and then observe the Elodea under the low power objective. Then switch to the high power objective.

10.  On a separate sheet of paper draw a few cells of Elodea with the salt solution. Note the shape of the cells and location of the chloroplasts. Label the chloroplast, cell wall, cell membrane, and cytoplasm.

11.  Carefully remove the slide and dispose of the sample and clean the slide and coverslip.

Conclusion:

1.  Describe the cells of Elodea when they were observed in the distilled water and the changes in the Elodea in the salt solution.

2.  Did the water move into or out of the cell? Explain what this is demonstrating?

3.  Could you see the cell membrane before you added the salt solution? Why or why not?

4.  Explain which term – osmosis or diffusion – better describes the process you observed in this activity. Why?

5. 

  1. Which of the following terms (hypotonic solution, isotonic solution, hypertonic solution) describes the salt solution in this activity?
  2. Aquarium water is an isotonic solution for Elodea cells. Predict what would happen if you replaced the salt solution with aquarium water in the slide you saved in step D. If you have time, test your prediction.

6.  Review the meaning of the word plasmolysis in the text. Explain whether this term applies to any of the changes that you have observed.

7.  Read the following statement before answering the questions:

  1. Elodea cells normally contain 1% salt and 99% water on the inside.
  2. Tap water contains 1% salt and 99% water.
  3. Salt water contains 6% salt and 94% water
  4. Salt water has a higher concentration of salt than fresh water or Elodea cells.
  1. Answer the following questions about the Elodea in tap water:
  2. What is the percentage of water outside the cell?
  3. What is the percentage of water inside the cell?
  4. Did the cell change shape? Explain.

ii.  Answer the following questions about Elodea in salt water.

  1. What is the percentage of water outside the Elodea cell at the start?
  2. What is the percentage of water inside the Elodea cell at the start?
  3. When will the water move across the cell’s membrane?
  4. Did the inside of the cell change shape? Explain.

Application:

8.  How might the use of salt for snow removal affect plants next to sidewalks or roadsides?