Direction and Concentration Gradients Essay

913 Words May 16th, 2013 4 Pages
Direction and concentration gradients
Bradley Benton
ABSTRACT
In this experiment, we will investigate the effect of solute concentration on osmosis. A semi‐permeable membrane (dialysis tubing) and sucrose will create an osmotic environment similar to that of a cell. Using different concentrations of sucrose (which is unable to cross the membrane) will allow us to examine the net movement of water across the membrane.
INTRODUCTION
A major determinant of diffusion in a biological system is membrane permeability. Small, uncharged molecules pass through cellular membranes easily, while most and/or charged molecules cannot pass through the membrane. The movement of water across a selectively permeable membrane, like the plasma membrane
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Submerge the four pieces of dialysis tubing into a 250 mL beaker filled with 100 ml of water for at least 10 minutes. After 10 minutes, remove one piece of tubing from the beaker on one end (not the whole tube), gently twirl the tubing into a long, thin cylindrical piece that is able to fit into the hole of the yellow bead. Insert the long cylindrical end of the tube into the center hole in the yellow bead. Once it is through, pull the cylindrical end until there is about 1.5 to 2cm of tubing extending beyond the bead. Take the extra tubing you just pulled through the bead and fold it back over the bead, towards the remaining, non folded tube. Place a rubber band above the bead and around the extra tubing as to be sure no solution can leak out of the tube. To test that no solution can leak out, add a few drops of water and look for water leakage. Make sure you pour the water out before continuing to the next step. Repeat steps 2‐4 with the three remaining dialysis tubes, using each of the three remaining bead colors Using a 10mL graduated cylinder, measure and fill the appropriate dialysis bag with the designated concentration of sucrose solution (3%, 15% or 30%) by adding the volumes of sucrose and water
YELLOW – BAG #1: 30% SUCROSE, STOCK SUCROSE: 10Mls, WATER: 0MLS
RED- BAG #2: 15% SUCROSE, STOCK SUROSE: 5MLS, WATER: 5MLS
BLUE- BAG #3: 3% SUCROSE, STOCK SUROSE: 1ML, WATER: 9MLS
GREEN- BAG #4: 3% SUCROSE, STOCK SUROSE: 1ML, WATER: 9MLS
Rinse the outside

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