Lab #7 Osmosis in Onion Cells

1. Lab #7 Osmosis in Onion Cells

2. Purpose • To study osmosis using onion cells.

3. 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.

4. 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)?

5. Materials • Microscope • Slide & cover slip • Onion • 15% NaCl water • Distilled water • Pipette

6. Procedure • 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. • Prepare a wet mount using the epidermis. • Make drawings and observations for the onion in low, med, and high power.

7. Procedure • Add 2-3 drops of 15% NaCl solution under the cover slip. Observe and draw the cells in low, medium and high power. • Add several drops of distilled water and wait about 2 minutes. Has the cell returned to normal? • Clean your slides and return the materials.

8. Data

9. Start • 15% NaCl • Distilled water

10. Conclusion • Summarize the lab and explain if the result support or reject your hypothesis. • How did the 15% NaCl solution affect the structure of the onion cell? Give a reason for why this occurred. • 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?

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