• Axes: Independent variable on the X-axis and dependent variable on the Y-axis. o Axes should also show the specific measuring units (e.g., minutes, grams, etc.) and values along each axis in regular increments (e.g., 0, 15, 20, 45, 60…). o If any of the bags have lost weight, you will need to have negative values on your Y-axis in addition to positive values. Your X-axis, therefore, may not be at the bottom of the graph; it may run along the center of the graph. Ask you instructor to explain if you do not understand this. • Key: Each bag should have a separate curve on the graph, and each curve should be labeled using colors or symbols and a key to identify each. The key should not just be labeled: Bag A, Bag B, etc., but should also explain the condition of each bag (e.g., Bag A: 1% sucrose in beaker containing 10% sucrose). Be sure that you are plotting Change in weight over time, NOT total weight over time. This means that all curves should start at the origin (0,0). Use a ruler to connect plotted data points for each bag. (This is a line graph, not a scatter plot with best fit lines!!) In addition to filling out Table 1 under Results, answer the questions under Conclusions. Observe diffusion across a differentially permeable membrane This exercise will be performed as a demonstration; you will still be responsible to observe and record the results. Dialysis tubing will be used as a model for a selectively permeable membrane. The pores in dialysis tubing are too small for large molecules, such as glucose, to pass through, but allow small molecules, such as water and ions, to freely pass into and out of the bag. Any substance small enough to pass through the pores in the dialysis tubing will do so according to the concentration gradient, if present. Bag 1 contains : water + phenolphthalein. This bag is placed into a beaker with 200 mL H 2 O plus 10 drops of 1 M NaOH. Phenolphthalein is a pH indicator and turns red/pink in a basic pH. It is colorless in neutral and acidic pHs. Bag 2 contains : 10 mL of starch. This bag is placed into a beaker with 200 mL H 2 O plus ~5 mL of iodine. Iodine is a starch indicator, turning dark blue/black in the presence of starch. Record your observations In Table 2 under Results, and answer the question in Conclusions. Observe Brownian movement 1. Add one drop of water to a clean slide. 2. Add a very small amount of Carmine red dye (powder) to the water drop using a metal spatula. The color should be just slightly pink. 3. Add a coverslip without incorporating any air bubbles. 4. Observe the dye particles under 400× total magnification. If you have too much water on the slide, you can wick some away with a Kimwipe. 5. Heat some coins in a boiling water bath. Carefully remove coins from boiling water with forceps. Place a coin on either side of the cover slip, and observe the dye particle again.
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- Fall '15
- Osmosis, Semipermeable membrane, bag