Hypothesis:
The difference of water potential between the cell’s cytoplasm and vacuole and the surrounding solution causes water to enter or leave the cell, resulting the change of the tissue’s mass.
Method:
- Prepare 18 potato slides, which each has a thickness of 4 to 5 millimetres, and divide them into 6 groups. Blot dry, weigh on a balance and mark down their weight as ‘ First weight’.
- Dilute the 10% sucrose solutions provided and thus provide six different sucrose solutions with concentrations of 10%, 5%, 2.5%, 1.25%, 0.6% and 0%.
- Put the samples into six test tubes containing the six different solutions and wait for 30 minutes.
- After 30 minutes, take out the samples from the test tubes. Blot dry and weigh again, mark down their weight as ‘ Second weight’.
Variables:
Dependent variable: changes in mass of potato slides
Independent variable: range of solutions
Other variables needed to be controlled: size of slides (4 to 5 millimetres each), time in solution (30 minutes), source of samples (from the same potato), and personal accuracy.
Prediction:
Some samples will weigh heavier since water enters the cell by osmosis; while some will weigh lighter since water leaves the cell by osmosis. There is the possibility that a sample will weigh the same, suggesting the cell has the same water potential as the surrounding solution.
Results:
Calculations:
According to the linear graph, the intercepting point is 7.1 percent. Therefore, the potato has a concentration of 7.1%.
Conclusion:
One sample weighs lighter, which suggests the potato slides lose water by osmosis and the potato has a higher water potential (lower concentration) than the 10% sucrose solution.
The rest of the samples all weigh heavier than before, which suggests that the slides absorbs water by osmosis and thus the potato has a lower water potential (higher concentration) than the 5% sucrose solution.
Comment:
According to the graph, we can see that as the concentration of the surrounding solution becomes lower, the change in weight increases. Placed in pure water, a plant cell becomes turgid because of the pressure generated by the cell wall which prevents more water from entering the cell.
YIN WENYI
15/10/2002
