Sweet Potato Lab - Lab PDF

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Li 1 Jenny Li Mr. Briggs AP Biology 28 November 2017 Water Potential of a Sweet Potato Lab Question: What is the water potential of a sweet potato? Claim: The water potential of a sweet potato is zero. Procedure: In this lab the purpose was to determine the water potential of a sweet potato. In this experiment, varying solutions of sucrose concentrations were used. The colored samples were red, pink, yellow, green, blue, and purple. To calculate the molarities of each colored solution, dialysis tubing was used to represent a model cell. A total of 6 dialysis tubes were used and each tube was filled with a different colored solution. They were then placed into a beaker of water and left to settle. Through the movement of water (osmosis), water traveled into the dialysis tubing if the colored solution had a higher concentration of sucrose. The dialysis tubings were weighed in order to determine exactly how much water traveled into the dialysis tubing. The greater amount of water that diffused into the dialysis tubing meant that the colored water had a greater concentration and molarity of sucrose than the water on the outside of the dialysis tubing. As a result, the varying sucrose concentrations of the colored solutions was used to determine the molarity of the sweet potato. The weight of each piece of sweet potato was measured prior to putting it into the colored solutions. After, the sweet potatoes were left to settle in the solution for multiple days in order to determine how much of each colored solution diffused into the sweet potato. The mass of the sweet potatoes was weighed. Afterwards, the percent change of the mass of the sweet potatoes was then calculated. The molarity of the sweet potato was calculated based on the colored solutions they were placed in. And finally, the molarity of the sweet potato was then used to determine its water potential. Data: Weight Change of the Sweet Potatoes in Varying Solutions Color of the Solution

Weight Before (g)

Weight After (g)

Change (g)

Percent Change

Red

1.6 g

1.6 g

0g

0.0 %

Pink

1.9 g

2.4 g

0.5 g

26.3 %

Yellow

1.7 g

1.9 g

0.2 g

11.8 %

Green

2.0 g

2.3 g

0.1 g

15.0 %

Blue

1.5 g

5.6 g

0.1 g

6.7 %

Li 2

Purple

1.8 g

2.4 g

0.6 g

33.3 %

Red = 1.0 M, Blue = 0.8 M, Yellow = 0.6 M, Green = 0.4 M, Pink = 0.2 M, Purple = 0.0 M Graph:

Conclusion: The data shows that in the red solution, there was no net movement of water because the weight of the potato before and after remained the same. This means that the molarity of the sweet potato is 1.0 M. This is because when two solutions are the same concentration (isotonic) there will be no net movement of water. The solute potential can be calculated with the formula: Ψsolute= -iCRT. Solute potential is the effect of solute concentration. It is known that the i is equal to 1 because that is the value for sucrose. C is the molar concentration from my data so it is also 1. The R is the pressure constant which is 0.0831. And T is in Kelvins so it is 273+room temperature. The room temperature was 22 degrees celsius so T is 295. After plugging each number into the formula, it is calculated that the solute potential is -24.514. In order to calculate the water potential, the formula Ψwater= ΨSolute + Ψpressure must be used. At equilibrium, the water potential is zero because no net water is going in or out of the cells. Knowing that water potential is zero and solute potential is -24.515, pressure potential can be calculated. So pressure potential is equal to the positive value of solute potential which is 24.515. Thus, the water potential of the sweet potato is zero given the results of the data that when the sweet potato is placed in the 1.0 M sucrose solution, the sweet potato is at equilibrium. Thus, based on the data, the water potential of the sweet potato in a 1.0 M solution is zero. Due to the fact that sweet potatoes are naturally sweet and they were placed in a sucrose solution, the results make sense. However, due to possible inaccuracies in data collection and the lack of running multiple trials, this value may be slightly off....