Water Potential

1 January 2017

Water potential is the measure of free energy of water in a solution. The purpose of this lab was to find the water potential of a potato cell. The problem of this lab was, if there was a high molarity of solute, would it have a positive or negative water potential? The hypothesis of the experiment was, if there is a high molarity of solute then the water potential would be lower or negative. After obtaining potatoes, we cut them into pieces, weighed them, and then placed them in a solution overnight.

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In this lab, we explored the potato cell’s water potentiality. From the results, we found that it the higher the molarity of a solution is, the lower the water potential of the potato cell. This finding supports our hypothesis. Introduction: Water will always move from an area of high water potential to an area of low water potential. Water potential is the measure of free energy of water in a solution. Water potential is represented by the symbol ? (psi). Water potential is affected by two physical factors.

One of factor is the addition on solute (? s); addition of solutes to a concentration will lower the water potential of that solute, causing water to move into the area. The other factor is pressure potential (? p). An increase of pressure potential raises the water potential. Water movement is directly proportionate to the pressure potential. The equation for water potential is: ? = ? p + ? s The water potential of pure water at atmospheric pressure is defined as being zero. The water potential value can be either positive, zero or negative.

An increase in pressure potential results in a more positive value, and a decrease in pressure potential results in a more negative value. In contrast to pressure potential, solute potential is always negative; since pure water has a water potential of zero, any solutes will make the solution have lower or negative water potential. In general, an increase in solute potential makes the water potential value negative and an increase in pressure potential makes the water potential more positive. Methods and Materials:

The materials used in this experiment were a large potato, peeler, apple corer, 250 mL beaker, paper towel, scale, six cups, knife, and about 100 mL solutions of: distilled water, 0. 2 M sucrose, 0. 4 M sucrose, 0. 6 M sucrose, 0. 8 M sucrose, and 1. 0 M sucrose. First, we poured 100 mL of assigned solutions into labeled cups. Then, my lab partner and I peeled a potato, and then sliced it. After slicing, we used an apple corer to cut it into pieces, and only using four pieces. Not including the skin.

Then we weighed the mass of the potato pieces before placing it in the solutions assigned by our teacher, and recorded. After, we placed them in solutions, and covered them with plastic wrap to prevent evaporation. And we left it to stand overnight. The next day, we removed the cores from the cups, blotted them, weighed the mass of the potato cores, and recorded the change in mass. We recorded the class data, and then calculated the percentage change. We then graphed our data and class data for percent change, and then determined the molar concentration potato cores.

Our hypothesis was that if there was a high solute potential then there would be a low or negative water potential. From the data, it clearly follows the rules of water potential. The higher the molarity is, the lower the water potential. The data verifies our hypothesis, making it true. Because there was a low water potential outside the potato pieces, it made the water inside the potato leave the cell, making it hypertonic. It is the opposite for the potato pieces in distilled water. There were no errors in this lab.

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