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Download MHP Lab 2 - Membranes
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Lab #2 Name:___________________________________ Membrane Function – Diffusion, Osmosis, and Endocytosis INTRODUCTION This lab will introduce you to cellular membranes, diffusion and osmosis (especially as they relate cell membranes) and receptor-mediated endocytosis. PURPOSE To gain a better understanding of diffusion and osmosis. To understand these terms: diffusion, osmosis, diffusion or concentration gradient, hyposmotic, hyperosmotic, isosmotic, hypotonic, hypertonic, isotonic, selectively permeable, semipermeable APPARATI AND MATERIALS DIFFUSION dialysis slide filled with water, starch solution or glucose solution beakers filled with water beakers filled with water and I2KI (Lugol's solution) stir plates magnetic stir bars test tubes boiling water bath Benedict’s solution water 15% glucose solution 1% starch solution OSMOSIS Elodea leaf microscope depression slides water NaCl solutions - 0.05M, 0.1M, 0.2M, 0.3M, 0.4M, and 0.5M sucrose solutions - 0.05M, 0.1M, 0.2M, 0.3M, 0.4M, and 0.5M microscope RECEPTOR-MEDIATED ENDOCYTOSIS actively growing amoeba proteus microscope slides petroleum jelly 0.001M alcian blue 0.01M sodium azide microscope GENERAL INFORMATION 1. Work in groups (the size of the groups will be determined by the size of the class and by the amount of equipment available). 2. Remember how to use and care for the microscopes from Lab#1. PROCEDURES A. Demonstration of Diffusion - Diffusion across a Semi-Permeable Membrane 1. A demonstration dialysis slide and a beaker of solution with the following contents will have been set-up before class: Sample Contents of Dialysis Slide Contents of Beaker 1 Starch Iodine 2 Glucose Iodine 3 Water Iodine 4 Starch Water 5 Glucose Water Based on an understanding of the dialysis membrane, what are your predictions regarding the movement of water molecules and solute particles when the dialysis slide is placed into the beaker? 2. 3. Record the colour of each solution at the beginning of the experiment. Wait until the colour changes begin to occur (usually 30 minutes). Record the results in the table provided in the results section. Add 5 mls of Benedict’s reagent to 9 separate tubes. For tubes 1-3, add 8 drops of water (tube #1), starch solution (tube #2), or glucose solution (tube #3). For the remaining tubes, add 8-10 drops from each of the beaker solutions into a separate tube. Record the colour of the solution. Boil the samples for 1-2 minutes. Record the colour of each tube in the table provided. B. Osmosis in a Plant Cell – NaCl-induced Cell Swelling or Shrinking 1. 2. 3. Obtain leaves from an Elodea plant. Assemble 7 depression slides (labeled with 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5) with one leaf in each slide. Place drops of salt solution on each depression slide, such that each slide has a different concentration of salt. Cover with a coverslip, and examine the material first at low power (100X) and then at high power (400X). Locate a region of typical cells and make a sketch in the boxes of Table 3 (below). Note especially the location of the chloroplasts. (Don’t forget to include total magnification.) Compare all the salt solutions. Repeat 1 and 2 using the sucrose solutions provided. C. Receptor Mediated Endocytosis 1. 2. Carefully make a ring of petroleum jelly on a microscope slide. Add a few drops of amoeba to the inside of the ring. Observe the amoeba under low magnification on the microscope. While looking under the microscope, add 10 l of 0.001M alcian blue dye. Record the results below. Set up a second amoeba slide. Add 10 ul of 0.01M sodium azide (careful!!) to the amoeba and let sit for 5 minutes before adding the dye. Repeat the rest of step 1. DATA SHEET NAME: __________________________ A. Diffusion Experiment Results: Table 1: Your Pre- and Post- Colour Observations from the Dialysis Slide Experiment Preexperimental contents (dialysis slide/beaker) Dialysis Slide Contents Preexperimental color Dialysis Slide Contents Postexperimental color Beaker Contents Preexperimental color Beaker Contents Postexperimental color starch/ iodine glucose/ iodine water/ iodine starch/ water Table 2: Benedict’s Test Results of Beaker Contents Tube Sample 1 water 2 1% starch 3 15% glucose 4 Starch/iodine beaker Glucose/iodine beaker Water/iodine beaker Starch/water beaker Glucose/water beaker 5 6 7 8 Preobservations PostObservations Glucose present? (y/n) glucose/ water Is there evidence of the diffusion of starch molecules? Is there evidence of the diffusion of iodine molecules? Is there any evidence for the diffusion of glucose molecules? What can you say about the permeability of the dialysis slide? (What particles could move through and what particles could not?) And what conclusions can you draw about your predictions? (Were you correct or incorrect with your predictions?) In this experiment, what was the independent variable? What was the controlled variable? What was the dependent variable? What were the negative and positive controls? B. Osmosis Experiment Results Table 3. Sketch your Elodea leaf cells here. Be sure to note your magnification and label your drawings! Water 0.05M NaCl 0.1 M NaCl 0.2 M NaCl 0.3M NaCl 0.4M NaCl 0.5M NaCl Water 0.05M sucrose 0.1 M sucrose 0.2 M sucrose 0.3M sucrose 0.4M sucrose 0.5M sucrose At what concentration of salt did the plant cells swell? At what concentration of salt did the plant cells shrink? At what concentration of salt did the plant cells stay the same? Which concentration of salt is isotonic? Hypertonic? Hypotonic? What concentration of sucrose was required to maintain the cell shape (the isosmotic solution)? Is it the same concentration of salt required to maintain the cell shape? Why? Assuming that the cells have not been killed, what should happen if the salt solution were to be replaced by water? Based on your observations, explain what happens on a cellular level when plants wilt from lack of proper watering. Can plant cells burst? Explain. D. Receptor-Mediated Endocytosis Results What happened to the blue dye? Did the amoeba take up the dye? Did the dye stay inside the amoeba? How did sodium azide affect the amoeba? What does sodium azide do? Explain your results. TO TURN IN: This lab report is due on Thursday (7/6). Turn in the answers to all of the questions posed in the text above. Include appropriately labeled drawings where requested.
