Lab _8 Osmosis in Onion Cells

							Lab #7 Osmosis in Onion
         Cells
             Purpose
• To study
  osmosis using
  onion cells.
      Background Information
• Osmosis is the movement of water through a
  selectively permeable membrane.
• Water moves from a low concentration of solutes
  to a high concentration.
• In the lab you will use a 15% NaCl (salt)
  solution. This solution has more solutes than
  the inside of the cell and is hypertonic.
• You will also use distilled water which is
  hypotonic when compared to the cell.
               Hypothesis
• What will occur to the onion cell if placed
  in a hypertonic solution (salt water)?



• What will occur to the onion cell if placed
  in a hypotonic solution (distilled water)?
                  Materials
•   Microscope
•   Slide & cover slip
•   Onion
•   15% NaCl water
•   Distilled water
•   Pipette
               Procedure
1. Remove a small section of tissue from
   the epidermis (skin) of the onion on the
   purple side. Once removed the
   epidermis is thin and almost transparent.
2. Prepare a wet mount using the
   epidermis.
3. Make drawings and observations for the
   onion in low, med, and high power.
              Procedure
4. Add 2-3 drops of 15% NaCl solution
   under the cover slip. Observe and draw
   the cells in low, medium and high power.
5. Add several drops of distilled water and
   wait about 2 minutes. Has the cell
   returned to normal?
6. Clean your slides and return the
   materials.
                    Data
Treatment   Observations


Starting


With 15%
NaCl
With
distilled
water
• Start



• 15% NaCl



• Distilled water
              Conclusion
1. Summarize the lab and explain if the
   result support or reject your hypothesis.
2. How did the 15% NaCl solution affect the
   structure of the onion cell? Give a
   reason for why this occurred.
3. In the winter, grass often dies near the
   roads that have been covered in salt to
   remove the ice. What do you think is the
   reason the grass dies?
              Conclusion



4. Define the following: isotonic, hypertonic,
   and hypotonic solution.
5. How do animal cells and plant cells react
   in a hypotonic solution?