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# AP Bio Water Potential and Diffusion Lab

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## Nikita Krushchev

on 7 December 2013

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#### Transcript of AP Bio Water Potential and Diffusion Lab

Background
Water Potential
Diffusion and Osmosis
Water potential is the relative measurement of water to move from one area to another, represented by Ψ
Water always moves from an area of higher water potential to lower water potential
Diffusion is the net movement of molecules or particles down their concentration gradient, requiring no energy
Osmosis is the net movement of water molecules through a semipermeable membrane from an area of high water potential to low water potential
Data
Sucrose Molarity in Potato
The red line indicates the point at which the line touches the x-axis.
The molarity of sucrose inside of the potato is 0.4M
Water Potential of Potato Cells
Since the water potential of the solution at equilibrium will be equal to the water potential of the potato cells and the solution is at equilibrium at 0.4M Sucrose then:

Ψˢ = -(1)(0.4 molelliter)(0.0831 liter bar/mole °K)(295 °K)
Ψˢ = -9.974 bars
Ψᵖᵒ = Water potential of potato cells = -9.974 bars
Question 1
If a potato were allowed to dehydrate in the open air, its water potential would decrease. The dehydration would cause the potato to lose water and thus gain solutes, decreasing the water potential.
If a potato core is allowed to dehydrate by sitting in the open air, would the water potential of the potato cells decrease or increase? Why?
Question 2
If a plant cell has a lower water potetial than its surrounding environment and if pressure is equal to zero, is the cell hypertonic (in terms of solute concentration) or hypotonic to its environment? Will the cell gain water or lose water? Explain your response.
The plant cell is hypertonic to its environment being that it has less water molecules and thus more solute concentration. The cell will gain water seeing as it has a lower water potential than its environment and that water flows from a higher water potential to a lower water potential
Question 3
If a student calculates that the water potential of a solution inside a bag is -6.25 bar (Ψˢ=-6.25, Ψᵖ=0) and the water potential of a solution surrounding the bag is -3.25 bar (Ψˢ=-3.25, Ψᵖ=0). In which direction will the water flow? Explain your response.
The water will flow into the bag. Using the equation Ψ = Ψˢ + Ψᵖ, at a pressure potential of 0, the water potential will be equal to the solute potential. Since the solute potential of the bag is lower than the surrounding area, the water will flow into the bag.
Question 4
The sucrose molarity of the zucchini cells is approximately 0.43M
Ψˢ = -(1)(0.43 molelliter)(0.0831 liter bar/mole °K)(300 °K)
Ψˢ = -10.7199 bars
Ψᶻ = water potential of zucchini cells = -10.7199 bars
Zucchini cores would be extracted from a zucchini and placed into different beakers of unknown sucrose molarities. The temperatures of the beakers would be recorded. Every 30 seconds for 5 minutes, the mass of the zucchini cores would be measured. The zucchini core that did not show a change in mass would have a solute concentration equal to that of the beaker. From this, we can gather than the Ψᶻ is -10.799 bars. This would cause the Ψˢ to be -10.799 bars. Solving for C, the molar concentration in the equation Ψˢ = -iCRT, we can find the solute concentration. C = 10.799/TR
Data
Question 1
Which substance(s) are entering the dialysis bag and which are leaving the bag? What experimental evidence supports your answer?
Water and glucose entered the bag. Sucrose left the bag.
Question 2
Which pair(s) that you tested did not have a change in weight? How can you explain this?
The Egg and NaCl pair did not change in weight.The concentration of NaCl in the egg was the same, so no diffusion had to occur.
Question 3
Predict what would happen to the mass of each bag in this experiment if all of the bags were placed in 0.4M sucrose solution instead. Explain your reasoning.
The mass of all of the bags would gradually decrease being that sucrose left the bag in presence of the egg.
Question 4
When a person is given fluid intravenously (an I.V.) in the hospital, the fluid is typically a saline solution isotonic to human body tissues. Explain why this is necessary.
This is to prevent water from entering or exiting the blood cells. If the fluid was hypotonic to the blood cells, in terms of salinity, water would enter the cells and cause them to burst. If the fluid was hypertonic, water would exit the blood cells and cause them to shrivel.
Question 5
A patient was given an I.V. bag with distilled water in it rather than saline solution. Describe what would happen to their red blood cells and explain why this would occur.
Water would enter the red blood cells and cause them to burst. There is a higher concentration of water outside of the blood cells, so water would enter the blood cells in order to reach equilibrium. They would burst and die.
Average change in mass of dialysis bags
Change in mass of potato cores
Conclusion
Water potential and diffusion work hand in hand, osmosis depending on the water potentials of two areas.
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