Red blood cells will burst if placed in distilled water (0% salt). Why didn’t the onion cells burst?
The number of plasmolyzed and unplasmolyzed onion cells in different concentrations of salt solution.
Salt concentration
Number of cells plasmolyzed
Number of cells counted
Percent of cells plasmolyzed
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%
Analysis and Discussion 1. Red blood cells will burst if placed in distilled water (0% salt). Why didn’t the onion cells burst? (Hint: what do plant cell have that animal cells don’t.) 2. Unfortunately the isotonic point doesn’t always give a good estimate of the actual concentration of solutes inside the cell. How does the concentration of solutes you found for onion cells compare to the concentration of solutes in sea water? If the solute concentrations are similar, why might this make sense? If they are not similar, what cell structures or mechanisms might help explain the difference? The Role of Evolution by Natural Selection Living cells and their membranes are much more complicated than the “model cell” you made out of semi-permeable dialysis tubing. In some plant species, plasmolysis is due primarily to the loss of water from the vacuole, a large storage chamber for relatively dilute fluids whose solute concentration may be lower than that in the cytoplasm proper. In other plant species, the cells may actually be able to resist plasmolysis in high-salt (hypertonic) environments due to properties of the cell membrane that actively pump solute ions in, or otherwise alter permeability of water and solute ions across the membrane. In your lab report, when you interpret your results from Part III, keep in mind that cells have adaptations that evolved for survival in hypotonic (freshwater) and hypertonic (marine/salt water) environments.