By: Youssef Gharib
Brief Description of Osmosis in Red Onion cells:
Osmosis is the diffusion of water from an area of low concentration to an area of high concentration across a semi-permeable membrane. The purpose of this lab is to compare the three different types of solutions affect on the relative size of the vacuole to the cell, the outer membrane of onion red cells (tunics) are used to figure out the different types. In the red onion you can see effects promptly when the onion cells are placed in different type of solutions. The effect of the solutions is shown through the purple part within the membrane since that’s where the vacuoles are present.
How will the vacuole inside the cells of the outer membrane of a red onion react when deionized water, a 1%, and a 10% saline solution are added to the cells?
If a saline solution is added to the outer membrane of a red onion cell, then based on the amount of the solution, it will cause the vacuole inside the cell to become hypertonic thus shrinking in size. This is because water moves from inside the vacuole, to the cell since the saline solution is entering the vacuole. While if deionized water is added on to cell, then the vacuole size should get larger or stay the same.
Independent Variables: type of solution, amount of solution, and the type of onion. Levels of IV: Deionized water, 1% saline solution, 10% saline solution, red onion outer membrane. Control group: Red onion without any solution added to it.
Dependent Variables: amount of water inside the vacuole.
1. Constant temperature - this will be insured by keeping the room at a constant temperature of 21 degrees, because if temperature is not kept constant, the data might be affected. 2. Type of onion - this will be insured by using the same onion (red onion) to collect data, if a different type of onion is used, this might cause the data to be inaccurate. 3. Microscope - while collecting data, and observing what happens to the red onion, the same microscope shall be used for observing what happens to the vacuoles.
* Red Onion
* Scissors/ Scalpel
* 1%, 10% saline solutions
* Deionized/Distilled water
* Plastic cups
* Cover slips
1.Take a small piece of onion and peel off a sheet of the purple skin. Cut a piece of skin about the size of a little fingernail.
2. Place the piece onto a microscope slide, and put it under the microscope to record data as this is the control group.
3. Then add five drops of deionized water onto the slide, then record qualitative and quantitative observations on the size of the vacuole inside the cell.
4. Then repeat step one, and put the piece of skin on another microscope slide.
5. Add five drops of 1% saline solution on the slide, then record qualitative and quantitative observations on the change in size of the onion cell vacuole.
6. Step four was repeated, then five drops of 10% saline solution were dropped onto the slide. Record qualitative and quantitative observations again on the change in size of the onion cell vacuole.
7. Steps 2, 3, 5, and 6 were all recorded under high-power objective in the microscope.
8. Clean and dry slide and coverslip.
The effect of Deionized water, 1%, and 10% saline solution on the outer membrane of a red onion Amount of water inside the vacuoles| No solution (control group)| Deionized water| 1% solution| 10% solution| Before| 100%| 100%| 100%| 100%|
After| 100%| 100%| 85%| 65%|
% change| 0%| 0%| 15%| 35%|
Qualitative data/ Observations| No change, purple onion cell walls only visible| No change, deionized water didn’t cause vacuoles to shrink| Vacuoles shrank, but not significant amount.| Vacuoles shrank a lot, and are visibly hypertonic|