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NAME: Review Questions 1. b. Explain why. 3. a. LABORATORY 6 DIFFUSION AND OSMOSIS 4. a. is the net movement of water through a selectively permeable membrane from an area of low solute concentration to an area of high solute concentration. Did the color change in the beaker, the dialysis bag, or both in Procedure 6.17 b. Explain how you determined this based on your results. DATE: For which dialysis bags in Procedure 6.2 did water move across the membrane? What salt solution (0%, 9%, or 5%) is closest to an isotonic solution to the potato cells in Procedure 6.5? b. Explain how you determined this based on your results. Would you expect a red blood cell to swell, shrink, or remain the same if placed into distilled water? 6. Explain why hypotonic solutions affect plant and animal cells differently. 7. Explain how active transport is different than passive transport. Laboratory 6. Diffusion and Osmosis: Review 79
8. Phenolphthalein is a pH indicator that turns red in basic solutions. You set up an experiment where you place water and phenolphthalein into a dialysis bag. After closing the bag and rinsing it in distilled water, you place the dialysis bag into a beaker filled with sodium hydroxide (a basic/alkaline solution). You observe at the beginning of the experiment both the dialysis bag and the solution in the beaker are clear. After 30 minutes you observe that the contents of the dialysis bag have turned pink but the solution in the beaker has remained clear. What can you conclude in regards to the movements of phenolphthalein and sodium hydroxide? Diffusion and Osmosis: Review Laboratory &
water always goes from low to high. 8. Allow the potato cylinders to sit for 60 minutes at room temperature, making sure to swirl the beakers every 20 minutes. 9. After 60 minutes, remove the potato cylinder from the 0% NaCl beaker and gently dry it using a piece of paper towel. 10. Weigh the potato cylinder to the nearest 0.1 grams and record the final weight in Table 6.4. 11. Repeat steps 9-10 for the remaining two beakers. 12. Calculate the percent change in weight by subtracting the initial weight from the final weight and then dividing by the initial weight. This number is then multiplied by 100. Reference the equation below. Percent change in weight = Final weight-Initial weight x 100 Initial weight Table 6.4: Effect of salt concentration on potato weight. Concentration of Salt Solution 0% 0.9% 5% Initial Weight of Potato Cylinder (g) 13.29 16.49 14.19 Final Weight of Potato Cylinders (g) 13.29 16-29 13.79 Percent Change in Weight 6.2 g 9.19 6.69 Procedure 6.5 Graph the Osmosis Data 1. Using the graph paper on the next page, construct a graph displaying the relationship between concentration of salt solution (%) and percent change in weight. 2. Remember the independent variable is always graphed on the x-axis and dependent variable on the y-axis. Include a description, correctly labeled axes, and values along each axis.
25% sucrose Bag A Bag B Bag C Bag A 10 mL 1% sucrose Bag D Dialysis Bag Contents Figure 6.3: Experimental setup up for Procedure 6.2. 10 mL of 1% sucrose solution Table 6.3: Contains total weights of dialysis bags collected at different time points. 15 min 30 min 45 min Weight Weight Weight (g) (g) (g) 15.29 14.19 1.59 12-39 10 mL of 1% sucrose solution 10 mL of 10% sucrose solution 10 mL of 25% sucrose solution 1% sucrose Beaker Bag B 10 ml 1% sucrose A 25% Sucrose Solution Bag C 10 ml 10% sucrose Initial Weight (g) Bag D 10 ml 25% sucrose B 196 Sucrose 10.59 16.89 11.89 11.09 Solution B 196 Sucrose 10.79 22.3g|11.99|11.69 Solution B 196 Sucrose 18.79 18.19 14.6g 14.2g 1% Solution 60 min obluedo Weight (g) Questions 1. In which dialysis bags did water move across the membrane? How were you able to determine this? Laboratory 6 Diffusion and Osmosis 71
6. Using a graduated cylinder, add 10 mL of starch solution and either clip, twistie tie, or knot the dialysis bag closed. Record the color in Table 6.2. 68 7. Rinse the outside of the dialysis bag with tap water and then submerge it in the beaker with lodine. 8. At the end of 30 minutes, record the color of both the solution in the beaker as well as that in the dialysis tubing and draw conclusions. $19 Figure 6.2: Preparation of the dialysis tubing. Table 6.2: Shows color change of solutions found either in the dialysis bag or in the beaker. Solutions Initial Color Final Color Conclusions Water+lodine low yellow Starch solution Clear Purple Beaker Dialysis Bag Questions 1. Did the color change in the beaker or the dialysis bag? Explain why this happened. 2. How is the dialysis tubing different than a cell membrane? Osmosis Osmosis is the net movement of water across a selectively permeable membrane from an area of low solute concentration to an area of high solute concentration. Another way of looking at this is that water is moving through a selectively permeable membrane from an area of high water concentration to an area of low water concentration, so osmosis is effectively the diffusion of water, The rate at which water or any other molecule moves depends on the concentration gradient between those two areas. The greater the concentration gradient, the faster the diffusion rate. For Diffusion and Osmosis Laboratory 6 bluedoor, LLC