Lab 6 - Biology 05LA Winter Quarter 2008 Lab 6 page 1 LAB...

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Biology 05LA – Winter Quarter 2008 Lab 6 – page 1 LAB #6: PROPERTIES OF BIOLOGICAL MEMBRANES The plasma membrane separates the cytoplasm from the environment, but it is much more than a simple barrier. The plasma membrane is a “selectively permeable” barrier that allows some sub- stances through more easily than others. The selectively permeable nature of this membrane is of great importance to the life of the cell. Not only is it involved in the control of solute traffic between the inside and the outside of the cell, but it is also important in the generation (or restriction) of directed water flow across the plasma membrane by the process of osmosis. Thus, there are few cellular functions that are not influenced in one way or another by this property of the plasma membrane. In this lab we will investigate the consequences of differences in total solute concentration between the cells interior and exterior, come to appreciate the meaning of the term “osmolarity”, and learn some of the physical and chemical properties of solutes that affect their permeability across the plasma membrane of red blood cells. When going through this lab exercise, think about the basic chemical and physical properties of the solutes that you will be using. In particular, are the solutes ionic, polar, or nonpolar in nature? Are they large or small? What is the effect of solute concentration vs. osmolarity? The nature of this lab is empirical, so think about the differences between the solutes and see if you can determine, for yourself, what ultimately determines the selective permeability of plasma membrane. * * * * * Note: The questions addressed in this lab are listed on the last page of this exercise. In addition to this write-up, information relevant to the “Introductions” to be prepared for this lab come from different areas of your text. Key words that will help you in your search are: solution, selective permeability, red blood cells and osmoregulaton. METHODS: Your TA will prepare the red blood cell (RBC) suspension that you will use for the various experiments and your spectrophotometric blank. This is done by adding 7 ml of sheep blood (purchased from a supply house) to 53 ml of isotonic saline. When 0.2 ml of this RBC suspension is added to 6.0 ml of isotonic saline, the resulting dilute suspension should have an optical density of about 1.0 when read at 600 nm. Your TA will check this at the beginning of your lab session. At this point, your group should obtain 10 ml of the RBC suspension for your experiments. Your TA will dispense this into a clean test tube which you take to your lab station and place into a small beaker that is partially embedded in ice – each lab bench will have an ice bucket for this purpose. EXPERIMENT 1
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Lab 6 - Biology 05LA Winter Quarter 2008 Lab 6 page 1 LAB...

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