Diffusion Osmosis Lab Part 1C

Introduction:

Water potential is a measurement of how likely it is that water will leave on place in order to go another. When in an isotonic solution, water potential will be lower since there will be no net movement of water. Water potential is dependent on the pressure potential and the solute potential. Adding both of these will yield the water potential. An increase in the solute potential will lower the water potential, while an increase in pressure potential will increase the water potential. In this experiment, potato cores and sucrose solutions, all of varying molar concentration, were used in order to determine the water potential of potato cores.

Procedure:

1. Pour 100 mL of the assigned solution into a labeled 250-mL beaker. Slice a potato into discs that are approximately 3 cm thick.

2. Use a cork borer (approximately 5 mm in inner diameter) to cut four potato cylinders. Do not include any skin on the cylinders. You need four potato cylinders for each beaker.

3. Keep your potato cylinders in covered beaker until it is your turn to use the balance.

4. Determine the mass of the four cylinders together and record the mass in Table 1.4. Put the four cylinders into the beaker of sucrose solution.

5. Cover the beaker with plastic wrap to prevent evaporation.

6. Let it stand overnight.

7. Remove the cores from the beakers, blot them gently on a paper towel, and determine their total mass.

8. Record the final mass in Table 1.4 and record the class data in Table 1.5. Calculate the percent change as you did in Exercise 1B. Do this for both your individual results and the class average.

9. Graph both your individual data and the class average for the percent change in mass in Table 1.4.

    

Conclusion/Analysis:

From this experiment it was possible to determine that the water potential of the potato cells was higher than that of the sucrose solution. After the 48 hours of having the potato cells be in the sucrose solution had passed, the potato cores were soggy and softer. It is possible that these observations were due to the loss of water from the cells, therefore indicating that the water moved from an area of high water potential to that of a lower one. For this reason, one can then determine that the water potential inside of the cells of the potato cores was higher than the water potential in the sucrose solution.

In order for the cells to reach an isotonic state, our individual group data showed that the net movement of water was zero when the potato cores were immersed in .3 M solution. This can found by analyzing Graph 1.2 and seeing that an isotonic state is when the potato cores are submerged in a .3M solution, since there is no net movement of water and no change in the potato core mass. Our data slightly differs from the class data. When analyzing the data from class in Graph 1.2, one can see that an isotonic state for the potato core cells is reached the potato cores are put in around a roughly 4.7M solution.