BIO101_Lab 5 Worksheets_Diffusion and Osmosis_Spring 2022

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Apr 3, 2024

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BIO 101 Lab 05: Diffusion and Osmosis v.2021 1 BIO 101 Lab 05: Diffusion and Osmosis **Note: Gloves will be needed for this laboratory experiment Objectives:____________________________________________________________ • Explain Brownian movement • Explain the concept of a selectively permeable membrane • Explain the concepts of diffusion and osmosis and why they are important to cell physiology • Use indicator chemicals to test for the movement of molecules and to determine the direction of diffusion • Explain the process of osmosis in living cells exposed to different extracellular solute concentrations Background:__________________________________________________________ Cells are surrounded by membrane that allows some substances to pass through, but not others. This is referred to as a selectively permeable membrane. There are several ways that nutrients, water, oxygen, carbon dioxide, and other molecules can be moved in and out of cells across the cell membranes. Two of these transportation methods are diffusion and osmosis, due to the fact that molecules are in constant motion. Brownian movement is another form of natural movement. It is the random movement of microscopic particles suspended in a liquid or gas caused by collisions with molecules of the surrounding medium. The process of diffusion occurs whenever molecules move from an area of high concentration to nearby areas where concentration is lower. Water molecules are no exception. Osmosis is the movement of water molecules from an area of high concentration to an area of lower concentration through a selectively permeable membrane. Both diffusion and osmosis are passive , meaning they do not require an input of energy. Active transport across the membrane requires energy (ATP) and requires a protein transporter. During osmosis water will move into or out of a cell based on the concentration of water on either side of the membrane. When the concentration of water is greater outside of the cell than inside the cell, the environment outside of the cell is called hypotonic. When cells are placed in a hypotonic environment osmosis will cause the cell to gain water, resulting in osmotic lysis in animal cells and increased turgor pressure in plant cells. When the concentration of water in the environment is less than inside the cell the environment is called hypertonic . When cells are placed in a hypertonic environment osmosis will cause water to leave the cell, resulting in crenation of animal cells or loss of turgor pressure in plants. The plasma membrane of plant cells in a hypertonic solution will peel away from the cell wall and shrink inward as the cell is being dehydrated.

BIO 101 Lab 05: Diffusion and Osmosis v.2021 2 This lab exercise will demonstrate the process of diffusion and osmosis in an experiment using dialysis tubing, a selectively permeable membrane with many small pores, which allows the passage of water molecules and small solute molecules but not large solute molecules. Materials:_____________________________________________________________ Experiment 1 • Microscope • Glass slide • Cover slip • Tooth pick • Carmine powder • Deionized water Experiment 2 • Dialysis tubing • Glass beaker • 25ml graduated cylinder • Test tubes • Iodine • Deionized water • Dialysis tubing clamps • Hot water bath • Sample stock solution • Benedict’s reagent • Silver nitrate Experiment 3 • Microscope • Glass slides • Cover slips • Elodea leaves • 20% saline solution • Deionized water Safety: Follow all standard laboratory safety procedures. Test tubes incubated in the hot water bath will be HOT to the touch. Use the tongs to remove the tubes from the hot water bath. Place hot tubes directly into tube rack. Lab coats are not to be worn outside of the lab. Procedure:____________________________________________________________ Experiment 1. Molecules in motion — Brownian movement 1. Work in groups. Get the following supplies: a glass slide, a cover slip, a dropper bottle of deionized water, a toothpick. 2. Place a drop of deionized water on the glass slide. Carefully add a tiny amount of carmine powder to the drop of water using the pointed tip of the toothpick. Use only a small amount of the carmine powder. ( Hint: obtain a very small amount on the tooth pick then use half of that ).

BIO 101 Lab 05: Diffusion and Osmosis v.2021 3 3. Add a cover slip to the glass slide and observe the slide under a microscope. Start with the 4X objective lens, then switch to the 10X, and eventually the 40X objective lens to see the movement of the carmine powder. 4. Leave the carmine powder sample in the full light of microscope for 5 minutes. Lower the light intensity for viewing purposes and observe the movement again. Describe the activity of the carmine powder in the water droplet. Record your observations in the Data Analysis and Synthesis Questions section below. Experiment 2. Diffusion and osmosis across semipermeable membrane (work in groups) 1. Wet a piece of dialysis tubing with tap water. Fold about one inch at one end of the dialysis tubing and seal it with a dialysis tubing clamp. 2. Measure 20 ml of stock solution (containing NaCl, glucose, and starch) using a graduated cylinder. Carefully pour the 20ml stock solution into the dialysis tubing through the open end. Seal this end as described in step 1. Make sure the dialysis bag is only half full. Invert the sealed tubing to ensure there are no leaks. 3. Measure the initial weight of the dialysis bag with its content using a balance and record the weight in Table 1. 4. Fill a 250 ml glass beaker half full with deionized water and keep the dialysis tubing in the water for 30 min. Once the tubing is in the water do not move or otherwise disturb the beaker of water or tubing. 5. Obtain 6 test tubes, label them with numbers 1 to 6. 6. Use a transfer pipette to transfer 1 dropperful of stock solution to tubes 1 to 3, 7. Use a fresh transfer pipette to transfer 1 dropperful of water from the beaker, specifically from the area surrounding the dialysis tubing, to tubes 4 to 6. 8. Add the individual reagents to the test tubes as described in Table 2, mix by gently shaking the tube, and record your observations. Remember to place the test tubes for the Benedict’s test in the hot water bath for 5 minutes to make the reaction happen. 9. Take the dialysis bag out of the beaker, briefly blot dry it on a paper towel and measure the final weight. Record the final weight in Table 1. 10. Based on your observations, make conclusions on the permeability of glucose, NaCl, and starch across the dialysis bag.

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