Lab #7 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
Starting
With 15%
NaCl
With
distilled
water
Observations
• 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?