Name__________________________________________
Red Onion Cell Plasmolysis (Practical 1b)
Date____________________
Procedure:
1. Using a fingernail or razor, remove a small piece of red onion skin (epidermis). It must contain cells
with the red pigment, and be very thin (ideally one cell thick).
2. Place the red onion skin, shiny side down, in the center of a clean slide
3. Add 1-2 drops of water to the slide and gently place a coverslip on the slide.
4. Observe the slide at 100X power, looking for undamaged cells with red pigment.
5. Complete a microscope drawing, following proper procedures, of the red onion epidermis in water.
Labels should include cell wall and tonoplast (large vacuole holding pink pigment) and cytoplasm,
nucleus and cell membrane if visible.
6. Carefully, use a dropper to add 1-2 drops of 10% NaCl solution to the edge of the cover slip, pulling the
water through the other side with a paper towel. Try NOT to move the slide so you can observe the
same cell if possible, but this is not required.
7. Immediately look through the microscope and observe continually. If plasmolysis occurs, it should be
very obvious. If not, you may need to remove the slide and soak the onion skin in the salt water before
continuing.
8. Once plasmolysis has occurred, complete a second microscope drawing of the plasmolyzed onion cells.
9. Dispose of onion skin in trash can. Wash and dry slides. Clean up materials and lab area.
You will submit your two completed microscope drawings.
Questions for group discussion:
Plasmolysis is the shrinking of the cytoplasm of a plant cell when water diffuses out of the cell
membrane.
1. Why did water diffuse out of the onion cells?
2. Describe how plasmolysis affected the structure of the plant cells, referring specifically to:
 Tonoplast
 Cell membrane
 Cell wall
3. How could you use this technique to determine which concentrations are hypertonic to red onion
cells?
4. Could you use a similar technique to determine which concentrations are hypotonic to red onion
cells?
5. How could you determine if plasmolysis is reversible?
6. The potato core lab looked at changes due to osmolarity at a macroscopic level and this lab looked at
changes at a microscopic level. What are the advantages and disadvantages of each technique?