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Diffusion/Osmosis Demonstration

Learn about the selective permeability of the cell membrane and the processes of diffusion and osmosis. Understand how substances move through the membrane and how to test for their presence using indicators.

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Diffusion/Osmosis Demonstration

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  1. Diffusion/OsmosisDemonstration

  2. The Cell Membrane is a selectively permeable tissue that surrounds the cell and its organelles. It allows only certain substances to enter or exit the cytoplasm and therefore acts as a “gateway” between the outside and inside environments. In order for a cell to maintain a healthy environment it must constantly bring in needed materials while removing waste products. Two processes are used to transport these materials into and out of the cell; diffusion and osmosis.

  3. Diffusion is the movement of particles from areas of high concentration to areas of low. These particles could be oxygen, carbon dioxide or nutrients. Osmosis is the movement of water from areas of high concentration to areas of low. All molecules travel in a solution, a mixture of two or more substances. The solvent is the part of the solution doing the dissolving, water is the universal solvent. The solute is what is being dissolved in a solution.

  4. Some substances can be tested for their presence in a solution through the use of an indicator. An indicator is any substance that changes color when in the presence of the substance it tests for. Iodine is an indicator for starch. When starch is present at the same time as iodine the iodine will turn blue-black. When not in the presence of a starch the iodine will remain a yellow-orange color.

  5. Before BEFORE Starch Solution Iodine Solution

  6. After Starch Solution Iodine Solution

  7. Yellow/Orange Clear Purple/Black Yellow/Orange

  8. Analysis • Define Diffusion: • Name three particles that move by diffusion: • Define Osmosis: The movement of particles from areas of high concentration to areas of low. Oxygen, Carbon Dioxide or Nutrients The movement of water from areas of high concentration to areas of low.

  9. Analysis • In this experiment, what is the solvent? • In this experiment, what is/are the solute(s)? • Define Indicator: • What is the indicator being used in this experiment? Water Iodine and Starch Any substance that changes color when in the presence of the substance it tests for. Iodine

  10. Analysis • What organelle does the dialysis tubing best represent? • What particles were able to move through the tubing? • Which particles were NOT able to move through the tubing? i. What is the characteristic called in which certain substances are allowed to move through the membrane? • Which process does this experiment best represent: Osmosis or Diffusion a. Why? Cell Membrane Iodine Starch Selectively Permeable Movement of particles

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