The Gate Keepers Examining Osmosis and Selective Diffusion

12 The Gate Keepers The Gate Keepers Examining Osmosis and Selective Diffusion OBJECTIVE Students will explain how membranes are semi-permeable and how that relates to plasma membranes. The students differentiate between hypertonic, hypotonic, and isotonic conditions and how it relates to the process of osmosis. Students will collect data, and determine the percentage of corn syrup that is isotonic to the egg. LEVEL Biology I NATIONAL STANDARDS UCP.1, UCP.2, UCP.3, C.1, E.1, E.2, G.2 T E A C H E R P A G E S TEKS 2(A), 2(B), 2(C), 2(D), 4(B) CONNECTIONS TO AP AP Biology: I. Molecules and Cells B. Cells 2. Membranes TIME FRAME 50 Minutes day 1 15 Minutes days 2 and 3 MATERIALS (For 28 students working in pairs) Part I 14 250 ml beakers 200 ml of 1% starch-15%glucose solution 14 vial glucose test tape 30 g glucose 14 12 cm of dialysis tubing (2.2 cm diam.) 2 g soluble starch 14 10 cc syringe (Note: 1cc=1mL) 500 ml of Lugol s iodine solution 10 g potassium iodide, KI 5 g iodine, I 2 404 Laying the Foundation in Biology

The Gate Keepers 12 MATERIALS, CONTINUED Part II lab apron and goggles 3 L vinegar several balances 3 L corn syrup 42 250 ml beakers 28 uncooked eggs 14 100 ml graduated cylinder paper towels aluminum foil 14 plastic spoons Part III lab apron and goggles 3 L vinegar several balances 3 L corn syrup 28 250 ml beakers 14 uncooked eggs 14 100 ml graduated cylinders paper towels 14 TI-83 graphing calculators (optional) aluminum foil 14 plastic spoons TEACHER NOTES This lab activity is designed to supplement a unit on the cell, cell transport, and homeostasis. Part I of this lab is a demonstration of the semi-permeable nature of cell membranes. It is recommended that the class does either Part II or Part III since it is time consuming to do both. Part II of this lab demonstrates the process of osmosis. In Part III, the student investigates the relationship between osmosis and varying concentrations of corn syrup and this part includes a strong math component. The sample data for Part III includes both 24 and 48 hour data. The trend is the same but more dramatic for 48 hours than 24. The relationship is not linear and therefore, a linear regression line or best fit line should not be drawn. T E A C H E R P A G E S Preparation of Solutuions 500 ml Lugol s iodine solution Dissolve 10 g of potassium iodide in 100 ml of distilled water. Add 5 g of iodine crystals to this solution. Add an additional 400 ml of distilled water. Stir until the iodine dissolves. Store the solution in an opaque or dark brown bottle. Be sure to use rubber gloves when making the above solution. 200 ml of 1% starch-15% glucose Dissolve 30 g of glucose and 2 g of soluble starch in enough distilled water to make 200 ml of solution. Hints The dialysis tubing must be soaked in water prior to use to make the tubing pliable enough to be opened. Laying the Foundation in Biology 405

12 The Gate Keepers To save on the expense of the glucose test paper, you may want to perform the test as a demonstration. Show the students that the iodine water does not have glucose and that the 15% glucose-1% starch solution does. Also the glucose test strips can be cut in half. If you do not have enough 250 ml beakers, use clear plastic cups that can be purchased at the local store. Students can supply the eggs and corn syrup. Use weigh boats or Petri dishes on the balance. Corn syrup can harm your balance. T E A C H E R P A G E S To save time, you can de-shell the eggs prior to the lab. Students may be curious as to why vinegar removes the shell. The vinegar contains acetic acid, which interacts with calcium carbonate in the shell to release carbon dioxide [hence the bubbles] and as result the outer shell softens since all of the calcium carbonate is removed. The shell was no longer present since it is essentially dissolved. The complete reaction is as follows: CaCO 3 + HC 2 H 3 O 2 CO 2 + CaC 2 H 3 O 2 ; the carbon dioxide bubbles away and the calcium acetate is soluble in water solutions. If you leave the egg out for 24 hours or so, the shell will harden somewhat as it incorporates carbon from the carbon dioxide in the air. Safety Alert Be sure to warn the students of the following: Warning: Lugol s iodine solution is poisonous if ingested. It is also a strong irritant and can stain clothing. Avoid skin/eye contact; do not ingest. If contact occurs, flush affected area with water for 10 minutes; rinse mouth with water; notify your teacher immediately. Warning: Be sure to wash your hands after handling raw eggs. Salmonella is bacteria commonly found in poultry and eggs. To avoid food poisoning, one should always wash their hands after handling raw eggs. 406 Laying the Foundation in Biology

The Gate Keepers 12 POSSIBLE ANSWERS TO THE CONCLUSION QUESTIONS AND SAMPLE DATA DATA AND OBSERVATIONS PART I Substance Present in the Beaker at the Beginning Data Table 1 Present in the Dialysis Tubing at the Beginning Present in the Beaker at the End Present in the Dialysis Tubing at the End Water yes yes yes yes IKI yes no yes yes Glucose no yes yes yes Starch no yes no yes Mass of egg in vinegar Mass of original egg Difference in mass Data Table 2 77.0 g 57.3 g + 19.7 g Percent change in mass + 34.0 % Mass of egg in corn syrup Mass of original egg Difference in mass 44.3 g 57.3 g 13.0 g Percent change in mass 23.0 % T E A C H E R P A G E S Mass of egg in water 59.5 g Mass of original egg 59.3 g Difference in mass + 0.2 g Percent change in mass + 0.34 % Laying the Foundation in Biology 407

12 The Gate Keepers T E A C H E R P A G E S Data Table 3 Results after 24 hours Egg 1 2 3 4 5 6 7 8 9 10 11 Percent Syrup Final Mass (g) Initial Mass (g) Change in Mass (g) Percent Change in Mass (%) 0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 % 84.6 77.3 79.1 73.7 61.9 56.4 56.8 55.5 57.9 56.7 50.9 79.5 76.9 85.7 87.8 81.5 80.4 85.4 85.4 91.3 91 83.1 5.1 0.4 6.6 14.1 19.6 24 28.6 29.9 33.4 34.3 32.2 6.42 5e 1 7.7 16.1 24 29.9 33.5 35 36.6 37.7 38.75 Results after 48 hours Egg 1 2 3 4 5 6 7 8 9 10 11 Percent Syrup Final Mass (g) Initial Mass (g) Change in Mass (g) Percent Change in Mass (%) 0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 % 85.5 81 82 77.5 59.5 52.6 50.7 47 50 45.1 41.8 79.5 76.9 85.7 87.8 81.5 80.4 85.4 85.4 91.3 91 83.1 6 4.1 3.7 10.3 22 27.8 34.7 38.4 41.3 45.9 41.3 7.55 5.33 4.32 11.7 26.9 34.6 40.6 44.9 45.2 50.5 49.69 408 Laying the Foundation in Biology

The Gate Keepers 12 CONCLUSION QUESTIONS PART I 1. What substances were permeable to the dialysis membrane? How do you know? H 2 O was permeable because the amount of liquid increased in the tubing. Glucose was permeable because the test tape showed that initially no glucose was in the beaker yet at the end of 30 minutes glucose appeared in the water in the beaker. Iodine was permeable because it crossed the membrane and reacted with the starch turning it purple. 2. Which substance was impermeable to the dialysis membrane? How do you know? Starch was impermeable because the solution in the beaker remained a golden brown color. If starch had crossed the membrane into the beaker, the solution would have turned purple. 3. Explain the concept of a selectively permeable membrane and how this relates to the dialysis tubing. There are pores in the dialysis tubing, and it is the size of the molecules and the size of the pore that determines what is permeable to the membrane. Large molecules cannot cross because they are too large to fit through the pores. Starch cannot cross because it is a macromolecule and is too large for the pores. On the other hand, smaller molecules move in and/or out of the dialysis tubing because they fit through the pores of the dialysis tubing. 4. This lab used glucose because it is permeable to the dialysis membrane. Glucose is a monosaccharide. Sucrose cannot be used because it is impermeable to the membrane. Sucrose is a disaccharide. Explain why sucrose is impermeable to the membrane and how the results of the experiment would change if sucrose were used. Sucrose, being a disaccharide, is twice as large as glucose and exceeds the pore diameter of the dialysis tubing. The results would have changed in that there would not be any sugar found in the water of the beaker after 30 minutes. T E A C H E R P A G E S PART II 1. What happened to the shell of the egg that was placed in the vinegar? The shell is dissolved by the reaction of the vinegar with the calcium carbonate in the shell. 2. What happened to the mass of the first egg after it was left in vinegar? Explain what accounts for the change in the mass of the egg in terms of osmosis. The mass of the egg increased as water entered the egg because the water was more concentrated on the outside of the egg than on the inside. The vinegar was hypotonic relative to the material inside the egg. Some molecules of vinegar also enter the egg. 3. What happened to the mass of the first egg after it was left in corn syrup? Explain what accounts for the change in the mass of the egg in terms of osmosis. Laying the Foundation in Biology 409

12 The Gate Keepers The mass of the egg decreased as water left the egg because the water was more concentrated on the inside of the egg than on the outside of the egg. The solution inside the egg was hypotonic relative to the corn syrup. 4. What happened to the mass of the second egg after it was left in water? Explain what accounts for the change in the mass of the egg in terms of osmosis. There was very little change in the mass of the egg because the calcium shell of the egg is waterproof not because the two liquids were isotonic. 5. If carrot sticks are put into water and refrigerated, they become turgid or stiff. If red blood cells are given the same treatment, they burst or lyse. What cellular structures account for the difference in the results? Plant cells have cell walls, which prevent them from bursting when water enters the plant cell. Animals do not have cell walls therefore as water enters the cell, the cell will burst. T E A C H E R P A G E S 6. A patient is brought into the emergency room. She is unconscious and is dehydrated. Will she be given an intravenous solution (IV) that is hypertonic, hypotonic, or isotonic to her red blood cells? Explain your answer. Remember that pure distilled water would be hypotonic to the patient s blood cells. She would be given an isotonic solution relative to blood plasma. If she were given just plain water, that is hypotonic relative to the blood cells, the blood cells would burst. If she is given a solution that is hypertonic to the plasma, the blood cells and tissues would lose water which would just aggravate the condition. PART III y y x x Results after 24 hrs. Results after 48 hrs. 7. According to the graph you have prepared from the class data found in Data Table 3, what percentage corn syrup solution is isotonic to the egg? The place where the line crosses the x axis is the point where there is no change in the mass of the egg. This is the point where the egg and corn syrup are isotonic. 410 Laying the Foundation in Biology

The Gate Keepers 12 8. Design a procedure to support that the percent of corn syrup isotonic to the egg, as interpolated from the graph, is correct. First, mix up the percent of corn syrup equal to the interpolated value of what would be isotonic to the egg. Mass an egg without the shell and submerge it into the corn syrup solution. After 24 hours, mass the egg again to see if there is a change in mass. If isotonic, there should be no change in mass. 9. What is the relationship between the percent change in mass and increasing amounts of corn syrup? With an increase in the percent of corn syrup, there is an increasing gain in percent change in mass. As percent concentration increases, change in mass increases. 10. At 100% corn syrup, was the egg hypertonic or hypotonic relative to the corn syrup? How do you know? The egg was hypotonic relative to the syrup, because the egg lost mass. 11. In distilled water, was the egg hypertonic or hypotonic relative to the corn syrup? How do you know? The egg was hypertonic relative to pure water because the egg gained mass. 12. Why would it be harmful to drink the ocean water if you were in a life boat on the ocean and thirsty? Sea water is hypertonic relative to blood. Because sea water is hypertonic, the body would actually lose water to the urinary system. Drinking sea water would make a person become more dehydrated. REFERENCES Diffusion and Cell Membranes, Biology: Principles and Exploration, Laboratory Experiments, Teacher s Edition. Austin: Holt, Rinehart and Winston, 1996. pp. 15 20 T E A C H E R P A G E S Haverson, Michael. http://www.the-aps.org/education outreach/outreach/acts-labs/halversn1.htm. How Do Hypotonic, Hypertonic, and Isotonic Solution Affect the Water Movement of a Cell (viewed October 1, 2003). Greenberg, Jon, Revision Editor. BSCS, A Molecular Approach. Chicago: Everyday Learning, 2001. pp. T41, 709 711 Laying the Foundation in Biology 411

12 The Gate Keepers The Gate Keepers Examining Osmosis and Selective Diffusion The cell membrane is a selectively permeable membrane that regulates what materials enter and leave the cell. There are some substances that are permeable to the cell membrane, such as water, oxygen, and carbon dioxide. Their ability to move into and out of the cell is a function of the Second Law of Thermodynamics and free energy. If a skunk sprays its perfume in a classroom, a student walking into the room can smell this odor. The student will be able to locate the source of the odor by tracing the odor along an increasing gradient to its source, the skunk. However, after enough time has passed, another student entering the room may be able to detect the odor but will not be able to locate the skunk. The preceding example is an illustration of the Second Law of Thermodynamics and free energy. When the spray is first released, it forms a small cloud of molecules that is relatively ordered. These molecules are in constant random motion and now have the freedom to move in any direction. It seems intuitive that out of the all the possible directions that the spray molecules will take, they will move away from the center of the cloud rather than towards it. These molecules are moving from an area of high concentration to an area of lower concentration. It is true that a small percentage of the spray molecules will move toward the center of the cloud, but the majority will move away from the center. The net movement of the molecules is away from the center of the cloud. In doing so, the spray forms a concentration gradient that the first student could follow to locate its source. As the molecules continue to move, they become more random, and they will become relatively equidistant from one another and a concentration gradient will no longer exist. Eventually this system will reach a state of equilibrium in which the perfume molecules will continue to move but there will be no net movement of the molecules. As a result, the second student entering the room will not be able to locate the skunk. This example follows the Second Law of Thermodynamics since this system over time becomes more disorderly as the molecules randomly move. The free energy of the molecules then decreases as they become more random and disorganized. Scientists summarize the movements of diffusion in a rule: substances tend to move from areas of higher concentration to areas of lower concentration. This difference in concentrations between two places is called a diffusion gradient or concentration gradient. When a substance is able to pass through a membrane, we say that the membrane is permeable to that substance. Membranes may be more permeable to some substances than to others. These membranes are referred to as selectively or differentially permeable. In other words, these membranes have different permeability to different substances; perhaps a small urea molecule will pass easily, but not a large starch molecule. Sometimes membranes do not permit substances to pass through at all. They are said to impermeable to that substance. Cell membranes are typically permeable to small, uncharged molecules such as water, carbon dioxide and oxygen. Osmosis is the special process of water moving across a membrane along a concentration gradient. Whether the net movement of water is into or out of the cell is a function of the osmotic gradient. When materials are impermeable to the cell membrane and are not in equilibrium, there is a net 412 Laying the Foundation in Biology

The Gate Keepers 12 movement of water across the membrane. The rule of thumb is water likes to dilute. Water, like other substances, will cross the membrane from where the water is most concentrated to an area where it is least concentrated. If a semi-permeable membrane separates two solutions, and those solutions are different in their concentrations, one can expect that there will be a net movement of water. The solution that has the greatest concentration of solutes is said to be hypertonic relative to the other side. The solution that has the least concentrations of solutes is said to be hypotonic relative to the other side. The net movement of water will be from the hypotonic side of the membrane to the hypertonic side of the membrane as water dilutes the side with greater amount of solutes. PURPOSE The purpose of this lab is to investigate the process of diffusion and osmosis through a semi-permeable membrane. It also explores the change in the mass of an egg, through the process of osmosis, with a change in the concentration of corn syrup. Your teacher may direct you to do either part II or part III, or both depending on the amount of time available to the class. Laying the Foundation in Biology 413

12 The Gate Keepers MATERIALS Part I 250 ml beaker 15 ml of 1% starch-15%glucose solution vial glucose test tape 10 ml of Lugol s iodine solution 12 cm of dialysis tubing (2.2 cm diam.) 10 cc syringe (Note: 1cc=1mL) Part II lab apron and goggles 200 ml vinegar balance 200 ml corn syrup 3 250 ml beakers 2 uncooked eggs 100 ml graduated cylinder paper towels aluminum foil plastic spoon Part III lab apron and goggles 200 ml vinegar balances 200 ml corn syrup 2 250 ml beakers 1 uncooked egg 100 ml graduated cylinder paper towels TI-83 graphing calculator (optional) aluminum foil plastic spoon Safety Alert Lugol s iodine solution is a poison if ingested. It is also a strong irritant and can stain clothing. Avoid skin/eye contact; do not ingest. If contact occurs, flush affected area with water for 10 minutes; rinse mouth with water; call your teacher immediately. Warning: Be sure to wash your hands after handling raw eggs. Salmonella is a bacteria commonly found in poultry and eggs. To avoid food poisoning, one should always wash their hands after handling raw eggs. 414 Laying the Foundation in Biology

The Gate Keepers 12 PROCEDURE PART I 1. Obtain one piece of dialysis tubing and tie a knot in one end. Open the other end of the tubing. This is best done with wet fingers rubbing the end of the tubing. 2. Use the syringe to put 10 cc of 15% glucose and 1% starch solution into the dialysis tubing bag. Note: (10 cc = 10 ml). Using glucose test tape, test the solution in the dialysis tubing for the presence of glucose. Record your findings in Data Table 1. 3. Tie the open end of the bag shut and wipe off the outside of the bag. 4. Fill a 250-mL beaker with 200 ml of water. Add 10 ml of iodine solution or enough that the water appears golden yellow. Using glucose test tape, test the solution in the beaker for presence of glucose. Record your findings in the data table. 5. Submerge the bag into the beaker of iodine and water. Allow the bag to remain in the solution for 30 minutes and observe the results. After the time has elapsed, test the beaker and the dialysis tubing for the presence of glucose. 6. Observe the dialysis bag and the solution in the beaker for evidence of the presence of starch. Remember that a blue to blue-black color indicates the presence of starch in an iodine containing solution. Record your findings in Data Table 1 on your student answer page. PART II 1. Obtain 2 raw eggs. Measure their mass to the nearest 0.1 of a gram. Record these original mass values in Data Table 2. 2. Pour 200 ml of vinegar into a 250 ml beaker and label it vinegar. Using a spoon, lower the egg into the beaker of vinegar. 3. Pour 200 ml of water into a second 250 ml beaker and label it water. Using a spoon, lower the second egg into the beaker of water. 4. Observe the eggs for a few minutes, then cover both beakers with aluminum foil. 5. After 1 2 days, observe what has happened to the eggs and how they have changed. Carefully remove the egg in water, dry it with a soft paper towel and mass it. Return the egg back to the beaker of water. Record your results in Data Table 2 on your student answer page. 6. Carefully remove the egg in the vinegar, dry it with a soft paper towel, and mass it. Record your results in Data Table 2 on your student answer page. 7. Pour 200 ml of corn syrup in a clean beaker and label it syrup. Carefully place the vinegar soaked egg in to the beaker of corn syrup. Laying the Foundation in Biology 415

12 The Gate Keepers 8. Cover both beakers with aluminum foil. Let them stand for 1 2 days. Clean your work station and wash your hands. 9. After 1 2 days, observe what has happened to the eggs and how they have changed. Carefully remove the eggs from the beakers and mass them. 10. Record your results in Data Table 2on your student answer page. Determine the % change in mass by using the following equation: ( final mass original mass) % change in mass = 100 original mass 11. Dispose of the eggs according to your teacher's instructions and clean the beakers and your work station. 12. Be sure to wash your hands after handling the eggs. PART III 1. Obtain a raw egg. Measure its mass to the nearest 0.1 of a gram. 2. Pour 200 ml of vinegar into a 250 ml beaker and label it vinegar. Using a spoon, lower the egg into the beaker of vinegar and cover with foil. After 1 2 days, the outer shell should be dissolved. 3. Your teacher will assign you a percent of corn syrup solution to make. If the solution you are assigned is not made, then make the assigned solution by following the appropriate recipe below. Use a 250 ml beaker for your solution. Percent Corn Syrup Amount of Corn Syrup Amount of Water 0% 0 ml 200 ml 10% 20 ml 180 ml 20% 40 ml 160 ml 30% 60 ml 140 ml 40% 80 ml 120 ml 50% 100 ml 100 ml 60% 120 ml 80 ml 70% 140 ml 60 ml 80% 160 ml 40 ml 90% 180 ml 20 ml 100% 200 ml 0 ml 416 Laying the Foundation in Biology

The Gate Keepers 12 Mix the solution thoroughly until the solution is homogeneous. If you are using a high concentration of corn syrup (80% or 90%), it is easier to mix 20 ml of the corn syrup with the water and then add the remaining corn syrup. 4. Carefully remove the egg from the vinegar, carefully dry it with a soft paper towel, and mass it. Record this as the original mass in Data Table 3. 5. Carefully place this egg in your assigned corn syrup solution and cover with foil. 6. Clean up your workstation. Be sure to wash your hands after handling the eggs. 7. After 1 2 days, observe what has happened to the egg and how it has changed. Carefully remove the egg from the beaker and carefully dry it, taking care not to break the membrane. 8. Mass the egg and record this as the final mass. 9. Determine the percent change in mass by using the following formula: 10. Collect the class data for all the eggs in the class. ( final mass original mass) % change in mass = 100 original mass 11. On your own graph paper, prepare a properly titled graph of the class data. Be sure to label it with the correct units and measurements. Be able to identify the dependent versus the independent variable. 12. Dispose of your eggs as instructed by your teacher. Clean up your workstation. Be sure to wash your hands after handling the eggs. 13. Answer the conclusion questions on your student answer page. Optional - The data can be graphed on a TI-83 graphing calculator by doing the following: 14. To make a data table press, then select EDIT (Figure 1) and press. Notice that there are columns or lists to record data. Laying the Foundation in Biology 417

12 The Gate Keepers Figure 1 Figure 2 15. To clear a list that might have data in it, put the cursor at the very top of the list so that the name of the column is highlighted. Press followed by the. 16. Now enter the percent of corn syrup in L1 starting at 0 for the first entry and ending at 100 percent for the last entry. In L2 record the corresponding initial mass. In L3 record the corresponding final mass. See Figure 2. 17. Calculate the percent change in mass in L4 by doing the following: a. Position the cursor at the top of L4 and press. Key in [L3] [L2] [L2] (see Figure 3) and then press (see Figure 4). b. To view this graphically, press,,. At this time make sure to put your cursor on PLOT 1 and press and move the cursor down to ON and press. Both PLOT 1 and ON should be highlighted. All other plots should be inactivated. Highlight the line plot (the second one of the graphs displayed) and press. Figure 3 Figure 4 418 Laying the Foundation in Biology

The Gate Keepers 12 18. Highlight the Xlist and press [L1]. 19. Highlight the Ylist and press [L4]. See Figure 5. 20. Press then press. A graph should appear that will automatically adjust the axes so that they fit the window. See Figure 6. Figure 5 Figure 6 Laying the Foundation in Biology 419

12 The Gate Keepers Name Period The Gate Keepers Examining Osmosis and Selective Diffusion DATA AND OBSERVATIONS PART I Data Table 1 Substance Present in the Beaker at the Beginning Present in the Dialysis tubing at the Beginning Present in the Beaker at the End Present in the Dialysis Tubing at the End Water IKI Glucose Starch Mass of egg in vinegar (g) Original mass of egg (g) Difference in mass (g) Percent change in mass (%) Data Table 2 Mass of egg in corn syrup (g) Original mass of egg (g) Difference in mass (g) Percent change in mass (%) Mass of egg in water (g) Original mass of egg (g) Difference in mass (g) Percent change in mass (%) 420 Laying the Foundation in Biology

The Gate Keepers 12 Data Table 3 Egg 1 2 3 4 5 6 7 8 9 10 11 Percent Syrup Final Mass (g) 0 % 10 % 20 % 30 % 40 % 50 % 60 % 70 % 80 % 90 % 100 % Initial Mass (g) Change in Mass (g) Percent Change in Mass (%) CONCLUSION QUESTIONS PART I 1. What substances were permeable to the dialysis membrane? How do you know? 2. Which substance was impermeable to the dialysis membrane? How do you know? Laying the Foundation in Biology 421

3. Explain the concept of a selectively permeable membrane and how this relates to the dialysis tubing. 4. This lab used glucose because it is permeable to the dialysis membrane. Glucose is a monosaccharide. Sucrose can not be used because it is impermeable to the membrane. Sucrose is a disaccharide. Explain why sucrose is impermeable to the membrane and how the results of the experiment would change if sucrose were used. T E A C H E R P A G E S PART II 1. What happened to the shell of the egg that was placed in the vinegar? 2. What happened to the mass of the first egg after it was left in vinegar? Explain what accounts for the change in the mass of the egg in terms of osmosis. 3. What happened to the mass of the first egg after it was left in corn syrup? Explain what accounts for the change in the mass of the egg in terms of osmosis. 422 Laying the Foundation in Biology

The Gate Keepers 12 4. What happened to the mass of the second egg after it was left in water? Explain what accounts for the change in the mass of the egg in terms of osmosis. 5. If carrot sticks are put into water and refrigerated, they become turgid or stiff. If red blood cells are given the same treatment, they burst or lyse. Account for the difference in the results. 6. A patient is brought into the emergency room. She is unconscious and is dehydrated. Will she be given an intravenous solution (IV) that is hypertonic, hypotonic, or isotonic to her red blood cells? Explain you answer. Remember that pure distilled water would be hypotonic to the patient s blood cells. PART III 1. According to the graph you have prepared from the class data found in Data Table 3, what percentage corn syrup solution is isotonic to the egg? 2. Design a procedure to support that the percent of corn syrup isotonic to the egg, as interpolated from the graph, is correct. Laying the Foundation in Biology 423

3. What is the relationship between the percent change in mass and increasing amounts of corn syrup? 4. At 100% corn syrup, was the egg hypertonic or hypotonic relative to the corn syrup? How do you know? 5. In distilled water, was the egg hypertonic or hypotonic relative to the corn syrup? How do you know? 6. Why would it be harmful to drink the ocean water if you were in a life boat on the ocean and thirsty? 424 Laying the Foundation in Biology

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