Osmosis

The purpose of this experiment was to test different solute concentrations on the rate of osmosis. Artificial cells were filled with different solute concentrations and placed in water and weighed at equal time intervals to show how the water moves across cell membranes and down its concentration gradient into the lower concentrated area. The weights of the cells were recorded each interval, and then the rate of osmosis was found by calculating the corrected cumulative change in weight.The prediction made was that the cells with the higher solute concentrations ould have a higher rate of osmosis and the cell filled with water and placed in 40% sucrose solution would have the highest negative weight change. Introduction The diffusion of free water across a selectively permeable membrane is called osmosis. A selectively permeable membrane allows certain substances to cross it more easily than others (Reece, et al. 2011). Osmosis is an important process to cells because the cells are co ntinuously trying to achieve concentration equilibrium.The tonicity of a solution is the ability to cause a cell to gain or lose water molecules (Reece, et al. 2011). If a cell is in an isotonic solution, the cell does not gain or lose any water molecules, causing the net gain of weight to be zero. If a cell is placed in a hypotonic solution, there is a higher solute concentration in the cell, making water molecules move into the cell to help reach equilibrium. This causes the cell to gain weight. If a cell is placed in a hypertonic solution, there is a higher solute concentration outside the cell, making water molecules leave the cell to attain equilibrium. This causes the cell to lose weight.Other factors, like the temperature, the particle size and the concentration gradient affect the rate of osmosis. An increased temperature can increase the rate of osmosis and osmotic pressure (Traxler 1928). Also, the particle size determines what can pass through the selectively permeable me mbrane; the channels imbedded in the membrane can only accommodate certain molecules based on size and function. Finally, the concentration gradient affects the rate of osmosis because the rate depends on how high the concentration of the solute is; the higher the concentration, the faster water moves to that concentrated area.Materials and Methods The materials needed for this experiment are: five strips of Spectra/Por 4 dialysis ubing with a pore size of 4. 8 angstroms, ten clamps, five beakers labeled 1 through 5, a graduated cylinder, and 20%, 40%, and 60% sucrose solutions. The experiment begins by softening up the dialysis tubes by soaking them in a beaker of water. When softened, rub the dialysis tubes between your fingers to reveal the opening and clamp the opposite end. Add 10 mL of the appropriate solution to each bag, squeezing the air out of the tube to make sure there are no air bubbles when clamping the other end of the tube.Three of these bags will be filled with 20%, 40% and 60% sucrose solutions. The other two will contain water. Weigh each bag on a appropriate solution, Just enough to cover the bag; four will have water and the fifth beaker will hold 40% sucrose. The bags containing 20%, 40% and 60% will be placed in water, as well as one bag filled with water; the bag of water in water will act as your control. The other bag of water will be placed in the beaker containing 40% sucrose solution. Place the five bags in their rightful beaker simultaneously and record the time.Every ten minutes the bags should be removed, blotted to get the excess solution off and then weighed. Continue weighing the bags every ten minutes or ninety minutes. To minimize experimental error, the temperature must be the same for all beakers and the bags must be blotted before weighed as much as possible to get the excess solution off. Also, the same amount of solution should be put into each beaker. Results The increase in the rate of osmosis is due to the different concentrations of sucrose, as shown in Figure One.This figure shows the weight change over time for the 20%, 40%, 60% and water in 40% sucrose solution. The results of the total weight change were: 20% sucrose in water= 5. 47 g 40% sucrose in water= 7. 31 g 60% sucrose in water= 7. 8 g Water in 40% sucrose= -4. 08 g The points plotted were used to calculate the rate of osmosis by finding the slope of the best fit line of each test. The results for the rates of osmosis were: 20% sucrose in water= . 0551 g/min 40% sucrose in water= . 0728 g/min 60% sucrose in water= . 0811 g/min water in 40% sucrose= -. 68 g/min The slopes have an increasing pattern as the sucrose concentration goes up. This means that the rate increases as the sucrose concentration increases. The corrected cumulative change in weight relates to the osmotic rate because it is divided by the time. The direction affects the rate because, if the direction of osmosis changes the rate becomes negative. Discussion The resu lts show that the solute concentration of the solution affects the rate of osmosis because the larger the concentration gradient, the faster osmosis occurs.This makes sense because the farther the cell is from osmotic equilibrium, it will gain weight faster (McCutcheon 1926). This supported our prediction. The increase in osmotic rate because of an increase in solute concentration is because water moves from a solution of low solute concentration to a solution with high solute oncentration. This means water rushes into a solute of higher concentration faster than a low concentration. This is why the artificial cell with 60% sucrose solution had the highest corrected cumulative change in weight and the fastest osmotic rate.The artificial cell containing water in 40% sucrose solution had a negative osmotic rate because water was leaving the cell and osmosis was occurring in the opposite direction. In this experiment, only one bag of water was placed in 40% sucrose solution. In other e xperiments, adding two more bags of water and placing them in 0% and 60% sucrose solutions could be tested to see if the rate of osmosis is similar performed to show temperature is a factor in osmotic rates by having the same solute concentration in solutions and placing bags filled with water into them, each having a distinct temperature.References McCutcheon M, Lucke B. â€Å"The Kinetics of Osmotic Swelling in Living Cells†. Laboratory of Pathology, School of Medicine, University of Pennsylvania. 1926. Reece JB, Urry LA, Cain ML, Wasserman SA, Minorsky PV, Jackson RB. Campbell Biology. Ninth ed. Pearson Education, Inc. 2011. Traxler RN. â€Å"The Effect of Temperature on Rate of Osmosis†. Journal of Physical Chemistry. 1928. 1 . This graph shows the corrected cumulative change in weight taken every ten minutes to study the rate of osmosis. . The data was collected by measuring the weight of each bag after 10 minutes and finding the difference in weight between the s tart of the experiment and each increment of time. 3. The graph shows that the higher in concentration of sucrose, the faster the rate of osmosis occurs meaning that concentration and rate of osmosis are directly related. Also, this graph displays the opposite happening when water was placed into sucrose, but is still directly related.