Diffusion and Osmosis Lab

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Diffusion and Osmosis Lab

Hemi Ryu

11/21/05

Per. 4B

Background Information:

        All atoms and molecules possess kinetic energy due to their constant motion. Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration and is caused by the atoms’ kinetic energy.

        Osmosis is the diffusion of water through a selectively permeable membrane, a membrane that allows the diffusion of only selected solutes and water. During osmosis, water moves from a region of higher water potential to a region of lower water potential until equilibrium is reached. Water potential is the measure of free energy of water in a solution.

        Cells have ways to move ions or molecules incapable of diffusion and osmosis into and out of themselves. This process is called active transport, where carrier proteins use energy from ATP to move substances across the cell membrane against a concentration gradient, from a region of lower concentration to a region of higher concentration.

Two solutions are either hypertonic, hypotonic, or isotonic to each other. Hypertonic describes a solution that has a higher solute concentration than another solution. Hypotonic describes a solution that has a lower solute concentration than another solution. Isotonic is used to describe solutions with equal solute concentrations.

Experiment 1: Diffusion

Hypothesis:

If a semi-permeable bag filled with glucose and starch solution is placed in a beaker of distilled water, then the glucose and starch will move out of the bag and water will move into the bag to produce an isotonic solution because diffusion and osmosis occur to produce equilibrium between two solutions when a concentration gradient is present.

Materials:

  • 15% glucose/1%starch solution
  • 30-cm piece of 2.5 cm bag of dialysis tubing soaked in water
  • Testape
  • 250 mL beaker
  • distilled water
  • IKI (Lugol’s solution)
  • Stopwatch

Procedure:

  1. Form a bag with the dialysis tubing.
  2. Place 15mL of the glucose/starch solution in the bag and record the color of the solution.
  3. Test the glucose/starch solution with glucose Testape and record the results.
  4. Fill the beaker two-thirds with distilled water and add 4 mL of IKI. Record the color of the solution. Test this solution with glucose Testape and record the results.
  5. Immerse the bag in the solution in the beaker.
  6. Wait 30 minutes then record the color of the solutions in and outside the bag.
  7. Test both solutions with glucose Testape and record the results.
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Data:

Analysis:

        Initially, there was starch and glucose present in the bag and water and IKI (iodine) present in the beaker. However, after the bag was immersed in the solution inside the beaker, glucose was present in the beaker solution. The starch remained in the bag because starch is a macromolecule and thus too big to diffuse through the semi-permeable membrane of the dialysis bag. The glucose, however, diffused into the outside solution because it can pass through the membrane. The dialysis bag turned black because iodine (IKI) diffused into the bag from the outside solution. An ...

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