Rate Of Osmosis

Rate of Osmosis vs Solute Concentration
Introduction: In nature, the quest to reach equilibrium, or the state of rest or balance due to the equal action of opposing forces (http://www.dictionary.com). Osmosis and diffusion are two ways that cells reach this equilibrium, without exerting energy. Due to the unique nature of the phospholipid bilayer, small molecules can pass through the semipermeable membrane easily, through diffusion (https://www.biologycorner.com). Water, however, has a slightly more difficult time diffusing, and diffuses in a different way, called osmosis. Osmosis involves aquaporins, specialized proteins in the phospholipid bilayer, to facilitate the diffusion of water across the gradient to reach equilibrium. Water potential, or the measure of potential energy that water has, is determined by solute concentration and pressure (https://www.boundless.com/biology/textbooks). The formula for water potential is as follows: ψ = ψP + ψS, where ψP equals pressure potential and where ψS equals solute potential (-iCRT). Cells need a small size so that they can have an equal
surface area to volume ratio so the cells can have a higher rate of diffusion as to regulate their internal concentrations quickly (http://morningsidemicro.wikidot.com). These experiments were conducted to determine how surface area of cells, solute concentration, and molarity of a solute effects water potential.
The first experiment involved agar cubes, each with a different surface area, to measure how surface area affects the rate of diffusion. In this experiment, the constants included 2% agar containing the pH indicator dye phenolphthalein, 1% phenolphthalein solution, 0.1M NaOH, 0.1M HCl, squares of hard, thin plastic (from disposable plates); unserrated knives; or scalpels from dissection kits, metric rulers, petri dishes or test tubes to hold the agar cubes. For the independent variable, the cubes were cut into different sizes to model different surface areas. Thus, the dependant variable was the rate of diffusion into the cell. For a control, an uncut agar cube was used. Two separate agar cubes were cut to serve as the experimental
groups. The second experiment was conducted to find the percent change of a mass of a dialysis bag with different solutions. For the constants, 1 M sucrose, 1 M NaCl, 1 M glucose, and 5% ovalbumin (egg white protein) were used as the solutions (Note: 5% ovalbumin = 5 g/100 mL = 50 g/liter. The MW of ovalbumin is 45,000 g/mole. The molarity of a 5% solution = mole/45,000 g 3 50 g/liter = 0.0011 M). Dialysis tubing (5 pieces per group), Balances, distilled water, volumetric pipettes, and graduated cylinders were used for preparing dilutions. There were two control groups, both with the 5% ovalbumin inside the dialysis bag, but one with distilled water outside, and on with the 5% ovalbumin solution on the outside. The experimental groups also had the 5% ovalbumin inside the dialysis bag, but different solutions, with the same molarity, outside the bag. The fourth experiment was conducted to observe osmosis in living Elodea cells. As a control, the Elodea cells were first observed in distilled water. The experimental corpse involved the Elodea being placed in hyper/hypotonic solutions to see the change in turgor pressure. For the control, the same leaf was used and the same molarity of the substances were used as well. In the final experiment, Ipomoea batatas (or sweet potatoes) were used to test the molarity of various mystery substances, each with an increasing molarity by a factor of .2. For a control, the same potato, balances, metric rulers, and sucrose in the solutions were constant. The control group was the potato in distilled water, and the experimental groups were the colored sucrose solutions. Hypotheses for each experiment are as follows. The first experiment’s hypothesis was that the smaller the cube, the larger the rate of diffusion, due to the surface area to volume ratio (http://morningsidemicro.wikidot.com). For the second experiment, the hypothesis was that the dialysis bag’s mass would increase for the solutions that were hypotonic to the bag, if the dialysis bag’s mass decreased, the solution was hypertonic to the ovalbumin. If the bag’s mass stays the same, then the solutions are isotonic due to water potential. The hypothesis for the third experiment was that once the Elodea is placed in the salt solution, the cell will shrivel, but when the cell is then placed in distilled water, then the cell will expand, due to a higher turgor pressure. For the final experiment, the hypothesis was very similar to the second experiment, if the potato’s mass decreased, the solution was hypertonic to the potato. If the potato's mass stays the same, then the solutions are isotonic because of water potential.