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 would 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 continuously 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...
References: McCutcheon M, Lucke B. “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. “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.
2. The data was collected by measuring the weight of each bag after 10 minutes and finding the difference in weight between the start 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.
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