Diffusion and Osmosis of Solutes and Water Across a Membrane

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Diffusion and Osmosis of Solutes and Water Across a Membrane Brittany Bacallao
Nova Southeastern University

Abstract:
This experiment gave a visual understanding of osmosis and diffusion. The first experiment proved that solutes would move down a concentration gradient if permeable to the selective membrane. The second experiment proved different solute concentrations affect the movement of water, depending on the solute concentration inside the cell. The purpose of this lab was to look for different solutes that can cross an artificial membrane and to observe the effect of different concentrations of sucrose on the mass of a potato cell. Results for Part One suggested that the molecular weight of albumin and starch was too large to pass through the dialysis tube, but glucose and sodium sulfate molecules were small enough to pass through the dialysis tube. Also, a decrease in water weight occurred due the dialysis tube being placed in a hypertonic solution. Results for Par Two showed the potato cell having a molar concentration of 0.2734, which caused sucrose concentrations above 0.2 M to have a decrease in mass. Inversely, sucrose concentrations below 0.2 M caused an increase in mass. Diffusion is the random movement of molecules spreading evenly into available space (Cain, Jackson, Minorsky, Reece, & Urry, 2011). Movement of water also follows a similar concept, however, water can act as a shield for solutes and become unavailable to diffuse while in other cases water is free and will move to an area of low solute concentration to an area of high solute concentration: this processes is better known as osmosis (Keith, Messing, Schmitt, & Feingold, 2010). Osmosis and diffusion can occur along a permeable membrane or selective membrane. A cell with a selective membrane allows small molecules and ions to pass through but excludes others; also, substances that are able to pass through the membrane do so at different rates. On the other hand, permeable membranes allow nonpolar molecules, such as hydrophobic molecules (water fearing), to dissolve in the lipid bilayer, which allows the molecule to easily cross the membrane. However, molecules such as glucose can pass through the lipid bilayer, but not as rapidly as nonpolar molecule (Cain et al., 2011). Understanding the concept of osmosis helps explain why lakes cannot have an increase in salinity. If saltiness of a lake increases, species living in the lake could die. This occurs when the lake water becomes hypertonic solution, which causes the animal cells to lose an excessive amount of water forcing the cell to shrivel up and die (Cain et al., 2011). On the contrary, understanding the concept of diffusion can help explain why after spraying perfume in one area of the room, then after several minutes, the perfume is smelled throughout the room. This is because particles of the perfume move randomly and eventually spread out evenly throughout the room. Moreover, in the experiment performed, diffusion and osmosis was observed using artificial systems (plastic membranes) and potato cells. The null hypothesis for Part One of the experiment is that the concentration gradient has no effect on the weight of the dialysis tube. The alternate hypothesis is that the weight of the dialysis tube will be affected by the concentration gradient. The null hypothesis for Part Two of the experiment is that the increase of sucrose concentration has no effect on the mass of the potato cell. The alternate hypothesis is that the difference in sucrose concentration will affect the mass of the potato cell. This experiment tests all hypotheses and helps to explain the concepts of diffusion and osmosis.

Materials and Methods:
Part One: Gloves were used to obtain a 20 cm section of dialysis tube that had soaked in a beaker of distilled water prior to the experiment. The dialysis tube was cleaned with distilled water and then tied off to form a pouch. Once the...
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