Lab 2 Rates of Diffusion_Osmosis_Filtration

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Rio Hondo College *

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226

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Biology

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Feb 20, 2024

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1 BIOL 226 (Human Physiology) Lab 2 Rates of Diffusion, Osmosis, and Filtration Diffusion is the major process that moves nutrients and waste between the outside of cells and the outside of blood vessels. Diffusion is caused by random molecular collisions. Factors affecting diffusion affect cell’s ability to have nutrient and waste exchange. Osmosis is the diffusion of water and the majority of what is inside of cells is water and the majority of what is outside of cell is water. Osmotic pressure causes osmosis. Factors that affect osmosis are essential to the well being of cells. Filtration is the major process that moves nutrients from blood into tissue fluid. The driving force for filtration is hydrostatic (fluid) pressure. The fluid inside of blood vessels causing hydrostatic pressure is blood, thus blood pressure directly affects filtration over capillaries. Only molecules small enough to fit between intracellular clefts and capillary pores are filtered. Factors affecting rates of filtration affect the amounts of nutrients available to cells. These experiments investigate factors that affect the rates of diffusion, including the molecular weight of a substance and the distance diffused. We will also investigate how molecular size affects osmosis. Finally, we will investigate how pore size, thickness of filtration membrane, and varying hydrostatic pressure affect the rates of filtration. Learning Objectives: *Explain what causes diffusion, osmosis, and filtration *Explain where diffusion, osmosis, and filtration occur in the body *Explain how molecular size and distance diffused affect the rates of diffusion *Explain how molecular size affects osmosis *Explain how membrane thickness, pore size, and hydrostatic pressure affect the rate of filtration *Explain how these variables affec t cells’ nutrient and waste exchange
2 A. Factors that affect the Rate of Diffusion 1. Molecular Weight of the substance diffusing substance Based on your results, what is the relationship between molecular weight of a substance and rate of diffusion? 2. Distance Diffused Procedure: Use the measurements from the graph above to fill out the table. Potassium permanganate Methylene blue How many mm diffused in 1 st 15 min How many mm diffused in last 15 min How did the rate of diffusion change as distance diffused increased? Explain why the rate of diffusion changed as the distance diffused increased. B. Diffusion through an Artificial Membrane (Dialysis) Procedure: Obtain one petri dish. Use forceps to place ONE crystal of potassium permanganate (MW = 158) and one crystal of methylene blue (MW = 320) on the agar equidistant from each other and the plate walls. Measure the distance diffused (diameter of the circle) in millimeters every 15 minutes for 1 hour. Graph the measurements below. Minutes mm mm Potassium permanganate Methylene blue 0 15 30 45 60 0 15 30 45 60 20 15 10 5 20 15 10 5
3 1. Prepare two dialysis bags containing the following: Bag 1 – protein solution Bag 2 – glucose solution (30% glucose). Rinse the outside of the bag with distilled water and blot dry. 2. Weigh each bag. 3. Fill two beakers about half full of distilled water. Place each bag in a separate beaker. Label the beakers (glucose or protein). Leave the bags in the beakers for one hour. 4. After one hour, remove each bag, blot it dry, and weigh each bag. 5. To determine whether protein and glucose have diffused out of the bags, perform the following chemical tests on the fluid from the beakers: Procedure: To prepare a dialysis bag, tie a thread or clip one side of the dialysis tubing. Open the other end and pour in a solution. Gently squeeze the bag to remove air and then twist and tie or clip the other end. a) Test for protein Place about 4 ml of water from the protein beaker in a clean test tube. Add 1 ml of Biuret reagent . If protein is present, the light blue solution will change to lavender. If there is no protein, the solution will remain light blue.
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4 Results: Bag Beginning Weight Ending Weight Weight Change Results of Chemical Tests Protein (Biuret Test) Glucose (Benedict’s Test) 1. Did protein diffuse out of the bag? Did glucose diffuse out of the bag? 2. What can you conclude about the pore size of the dialysis tubing and the molecular size? 3. Did osmosis occur during this experiment? How do you know? b) Test for glucose Place approximately 5 ml of water from the glucose beaker in a clean test tube. Add 2 ml of B enedict’s reagent . Place the test tube n boing water for two minutes. If glucose is present, the light blue solution will change to orange or green. If there is no protein, the solution will remain light blue.
5 C. Factors that Affect the Rate of Filtration NOTE: For all parts of this experiment, use the set-up diagramed below . 1) Size of Filtration Membrane Pores and the Rate of Diffusion a) Place one piece of filter paper (#1 with small pores or #4 with large pores) into the funnel and moisten the paper with water. b) Pour 10 ml of the protein-glucose solution into the funnel. Measure the amount of filtrate formed in 30 seconds. c) Find a group with the other filter paper and trade results. d) Record the results below. 2) Thickness of the Filtration Membrane and the Rate of Filtration a) Place two pieces of filter paper (#1 with small pores or #4 with large pores) into the funnel and moisten the paper with water. b) Pour 10 ml of the protein-glucose solution into the funnel. Measure the amount of filtrate formed in 30 seconds. c) Find a group with the other filter paper and trade results. d) Record the results below. 1 sheet #1 filter paper 1 sheet #4 filter paper 2 sheets #1 filter paper 2 sheets #4 filter paper Increased pressure (#1) Amount of filtrate formed 3) Hydrostatic Pressure Gradient and the Rate of Filtration a) Place one large piece of #1 filter paper into the funnel and moisten the paper with water. b) Pour 25 ml of the protein-glucose solution into the funnel. Measure the amount of filtrate formed in 30 seconds. d) Record the results below.
6 1. Were both solutes filtered? How do you know? 2. How did the size of the membrane pores affect the rate of filtration? 3. How did the thickness of the filtration membrane affect the rate of filtration? 4. How did the increase in pressure affect the rate of filtration? Lab Report Questions 1. What causes diffusion? What causes osmosis? What causes filtration? 2. If glucose and protein are in the tissue fluid, which would reach the cell faster? Why? How would it get to the cell? 3. How can the kinetic energy of individual particles be increased? How can the number of molecular collisions be increased without increasing the kinetic energy of individual particles? 4. If we used dialysis tubing with larger pores, would the rate of diffusion increase? Explain. 5. How can tissue fluid (normally) isotonic become hypertonic? Describe two different ways this can happen. 6. How would an increase in blood pressure affect the delivery of nutrients to cells? 7. In certain diseases, the basement membranes of capillaries are thickened. Which process would be most affected by this disease? What consequences does this have for the cells near these capillaries?
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