Osmosis and Diffusion Lab
Pre-Lab
a) When white vinegar was added to the combination of Agarose, phenolphthalen, and NaOH, the solution turned from bright neon pink to clear liquid in the class demonstration.
b) In the diffusion demo with the 'Party Gel,' a star shape and a heart shape were cut out of the phenolphthalen solution and placed into a separate dish. White vinegar was poured onto the shapes and we observed as the acid reacted with the base to determine which shape diffused faster. After watching for ten minutes, the star shape appeared to have diffused faster out of the two because it had a greater surface area (which is as predicted). The shapes were left overnight so that they could completely diffuse and the result was complete clarity in both shapes without a trace of neon pink.
b) In the diffusion demo with the 'Party Gel,' a star shape and a heart shape were cut out of the phenolphthalen solution and placed into a separate dish. White vinegar was poured onto the shapes and we observed as the acid reacted with the base to determine which shape diffused faster. After watching for ten minutes, the star shape appeared to have diffused faster out of the two because it had a greater surface area (which is as predicted). The shapes were left overnight so that they could completely diffuse and the result was complete clarity in both shapes without a trace of neon pink.
Lab Procedure
Hypothesis: The weight of each sweet potato piece will determine whether the solutions are hypotonic, hypertonic, or isotonic.
Dependent Variable: The weight of each sweet potato piece.
Independent Variable: The type of solution.
Materials: 5 sucrose solutions in different colors and different beakers, a sweet potato, a timer, a knife, labels, a scale, and a small potato corer.
1) Pour an equal amount of different concentrations of sucrose into five beakers (0.8 M, 0.2 M, 0.6 M, 0.4 M, and 1.0 M).
2) Label the beakers A-E.
3) Use the potato corer to core out five pieces of sweet potato.
4) Cut the sweet potato pieces so that they are similar in size.
5) Individually weigh and record each sweet potato piece.
6) Place a piece of potato in each beaker and set the timer for 15 minutes.
7) After 15 minutes has passed, remove the sweet potato pieces from their sucrose solutions and weigh them to record any change in weight.
8) Put the potato pieces back into their designated solutions and set the time for 5 more minutes.
9) After 5 minutes, record their weights again and observe any weight changes.
Dependent Variable: The weight of each sweet potato piece.
Independent Variable: The type of solution.
Materials: 5 sucrose solutions in different colors and different beakers, a sweet potato, a timer, a knife, labels, a scale, and a small potato corer.
1) Pour an equal amount of different concentrations of sucrose into five beakers (0.8 M, 0.2 M, 0.6 M, 0.4 M, and 1.0 M).
2) Label the beakers A-E.
3) Use the potato corer to core out five pieces of sweet potato.
4) Cut the sweet potato pieces so that they are similar in size.
5) Individually weigh and record each sweet potato piece.
6) Place a piece of potato in each beaker and set the timer for 15 minutes.
7) After 15 minutes has passed, remove the sweet potato pieces from their sucrose solutions and weigh them to record any change in weight.
8) Put the potato pieces back into their designated solutions and set the time for 5 more minutes.
9) After 5 minutes, record their weights again and observe any weight changes.
Data
Observations: Solution C's potato sunk to the bottom instead of floated on the surface of the liquid like the other potatoes in their solutions. There was not much change in weight after leaving the potatoes in the sucrose solutions for the designated time.
Conclusion Questions
a) List the solutions in order from most concentrated to least concentrated according to your data. According to your data which solutions match the water potential of the potato?
A, B, D, C, E.
Solutions A,B, and D match the water potential of the potato because they did not gain weight.
b) Given the following concentrations, calculate the solute potential of each solution assuming we kept a constant temperature of 22 degrees C in the beakers.
A(0.8M): iCRT = -(1)(0.8)(0.0831)(295) = -19.6116
B(0.2M): iCRT= -(1)(0.2)(0.0831)(295) = -4.9029
C(0.6M): iCRT= -(1)(0.6)(0.0831)(295) = -14.7087
D(0.4M): iCRT= -(1)(0.4)(0.0831)(295) = -9.8058
E(1.0M): iCRT= -(1)(1.0)(0.0831)(295) = -24.5145
Did your list match the actual concentrations?
The overall list of sucrose solutions did not match the water potential of the potato because some samples remained the same in weight.
c) We used plant cells for this experiment. If we left them over the weekend would the plant cells in a hypotonic solution burst? Why or why not?
No, the plant cells in a hypotonic solution would not burst due to the surrounding cell wall. However, the amount of water gained will cause the cell to become pressurized to the point where the water will not continue to enter the plant cell.
d) Could this experiment be done as effectively with animal cells/tissue? Explain.
No this experiment would not be as effective with animal cells or tissues because animal cells do not have a cell wall to regulate the amount of sucrose going in and out of the cell. Turgor pressure only exists in plant cells due to the pressure emitted from the cell wall's regulation of substances, so the iCRT equation will not work the same due to the pressure equaling zero.
e) Sources of error?
There was water on the scale while the potatoes were being weighed which could have skewed the weights of the potato pieces thus changing the results of the experiment. The amount of sugar that was already in the sweet potato may have accounted for the lack of weight gain or loss and diffusion of the sucrose.
A, B, D, C, E.
Solutions A,B, and D match the water potential of the potato because they did not gain weight.
b) Given the following concentrations, calculate the solute potential of each solution assuming we kept a constant temperature of 22 degrees C in the beakers.
A(0.8M): iCRT = -(1)(0.8)(0.0831)(295) = -19.6116
B(0.2M): iCRT= -(1)(0.2)(0.0831)(295) = -4.9029
C(0.6M): iCRT= -(1)(0.6)(0.0831)(295) = -14.7087
D(0.4M): iCRT= -(1)(0.4)(0.0831)(295) = -9.8058
E(1.0M): iCRT= -(1)(1.0)(0.0831)(295) = -24.5145
Did your list match the actual concentrations?
The overall list of sucrose solutions did not match the water potential of the potato because some samples remained the same in weight.
c) We used plant cells for this experiment. If we left them over the weekend would the plant cells in a hypotonic solution burst? Why or why not?
No, the plant cells in a hypotonic solution would not burst due to the surrounding cell wall. However, the amount of water gained will cause the cell to become pressurized to the point where the water will not continue to enter the plant cell.
d) Could this experiment be done as effectively with animal cells/tissue? Explain.
No this experiment would not be as effective with animal cells or tissues because animal cells do not have a cell wall to regulate the amount of sucrose going in and out of the cell. Turgor pressure only exists in plant cells due to the pressure emitted from the cell wall's regulation of substances, so the iCRT equation will not work the same due to the pressure equaling zero.
e) Sources of error?
There was water on the scale while the potatoes were being weighed which could have skewed the weights of the potato pieces thus changing the results of the experiment. The amount of sugar that was already in the sweet potato may have accounted for the lack of weight gain or loss and diffusion of the sucrose.