A.P. Biology Lab: 1. Osmosis

Topics: Osmosis, Concentration, Regression analysis Pages: 5 (1627 words) Published: November 15, 2010
Natalia Wierzchon
A.P. Biology Lab: 1. Osmosis
I. Introduction
a. Purpose: The purpose of this lab was to observe the diffusion process of water, osmosis, as well as create an understanding of water potential, the basis of osmosis. The experiment proved how water molecules in a solution are able to move from an area of low solute concentration, high water concentration, to an area of high solute concentration, low water concentration, diffusing “down” the water gradient. The movement of solutes from the area of high concentration to the area of lower concentration that surrounds them will be tested to hopefully demonstrate the accuracy of osmosis, as determined by the water potential equation, that uses pressure potential and solute potential to predict the direction of osmosis. b. Hypothesis: Based on results obtained from the water potential equation, I synthesize that when placed in a hypertonic solution, a potato core will have positive water potential in respect to its environment, meaning the direction of osmosis will be from the potato to the solution. II. Materials & Methods

a. Procedure:
i. Obtain all necessary materials for the experiment: the assigned sucrose solution for the group (.2M, .4M, .6M or .8M), an Erlenmeyer flask and corresponding cork, one or two skinless potato cores, scale to mass potato cores, paper towels and tables to record results. ii. Pour assigned solution into the Erlenmeyer flask ~200mL iii. Measure and record the mass of potato cores, zeroing the mass with paper or weighing tray on it, before massing the cores. iv. Submerge your cores entirely in the solution, cork the flask, and let sit 24-48 hours. v. Uncork the flask, draining the solution out before gently removing the potato cores onto some paper towels. vi. Pat the potato dry, but not completely dehydrated, before finding a final mass, by the same way as the initial mass. vii. Calculate percentage change from initial to final by subtracting intial mass from final, and dividing by final, and graph data, including that from class. b. Control: The control for this experiment will be potato cores submerged for the same period of time in the same volume of destilled water, which does not have any ions of macromolecules dissolved in it, while the potato cores certainly do, so the opposite should be true than of the hypothesis, the potato should be pulling water in for a positive instead of negative percent change in mass.

III. Data/Results
a. Data Table: The following data table represents the data collected from the class, where each group was assigned a concentration of sucrose solution to test on their potatoes. Each row shows the values from each concentration’s group, while each column compares the results for the same thing from each group. The obtained values were initial mass, final mass, change in mass, and percent change in mass [columns]. The table contains both positive and negative values in the last two columns, and positive values in the first two.

|Concentration |Initial Mass (g) |Final Mass(g) |(Mass(g) |%(Mass | |1.0 M |3.89 |2.39 |-1.5 |-39% | |.8M |3.06 |2.11 |-.95 |-31.04% | |.6M |2.23 |2.03 |.20 |-8.97% | |.4M |3.40 |3.76 |.36 |10.5% | |.2M |1.16 |2.02 |.86 |74.1% | |0M* |--...
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