Name Date. In this lab investigation you will investigate the movement of water through a selectively permeable membrane.

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1 This lab will be hand-written in your data book AP Osmosis Labs Part A (was done in previous a previous class: Dialysis tube + Starch + Glucose) Part B: Osmosis Unknowns In this lab investigation you will investigate the movement of water through a selectively permeable membrane. A laboratory assistant prepared solutions of 0.8 M, 0.6 M, 0.4 M, and 0.2 M sucrose, but forgot to label them. After realizing the error, the assistant randomly labeled the flasks containing these four unknown solutions as flask A, flask B, flask C, and flask D. Sucrose is known to be too large to fit through the membrane. Materials: 25cm strips of presoaked dialysis tubing String Beakers of unknown molar concentrations of sucrose solution. Plastic cups Electronic balance and measuring boat Any other materials needed; just ask the teacher. Introduction: Design an experiment, based on the principles of water potential, diffusion, and osmosis, that the assistant could use to determine which of the flasks contains each of the four unknown solutions. Background: Define each of the following terms and explain how each will play a role in your lab: a) osmosis b) water potential c) semipermeable membrane Purpose: (write your own in your data book writeup) Hypothesis: (write your own in your data book writeup) Procedure: 1. Design your own lab investigation. 2. Keep in mind the following procedures and precautions: a. Keep the bags moist during the entire lab. b. To make a dialysis tube: 1. Twist the bag at one end. 2. Tie a knot with the twisted end. 3. Using a pipette, add approx ml of the desired solution into the other end of bag (the contents should fill only about one-third to one-half of the tubing) 4. Squeeze out any remaining air from the tube. 5. Twist and tie the bag at the open end. 6. Rinse the outside of the bag. Analysis (answer in your data book)

2 Your data will be recorded in your lab books, but this informal lab will be presented in a mini-poster symposium AP Osmosis Lab Part C: Apples Read this procedure completely before completing the Prelab below, and complete the Prelab before coming to class to carry out the lab. Introduction: You will continue to investigate osmosis and water potential by studying different varieties of apple. Prelab: (Construct tables in the Results section of your data book and answer the questions in the space provided below) Make a table in your Results section, Titled Table 1.4: _<insert descriptive title here>_ and add your own descriptive title. Make a table in your Results section, Titled Table 1.5: _<insert descriptive title here>_ and add your own descriptive title. a) When your apple s cells are in a hypertonic sucrose solution, what will be true of the % change in mass of the apple? b) When your apple s cells are isotonic with the sucrose solution, what will be true of the % change in mass of the apple? c) When your apple s cells are in a hypotonic sucrose solution, what will be true of the % change in mass of the apple? Purpose: What is the molar concentration of sucrose in various varieties of apple, in the species Malus domestica? Hypothesis: construct a hypothesis that explains how you will know the molar concentration of sucrose in your apple. Materials: Apples (class will choose two different varieties to investigate, but your group will use just one of those varieties) Sucrose solutions in concentrations of 0.0M, 0.2M, 0.4M, 0.6M, 0.8M, 1.0M Electronic balance Plastic cups ( beakers ) Procedure: Work in groups of 3 or 4. Using your chosen variety of apple, do the following: 1. Obtain 6 plastic cups and label them 0.0M, 0.2M, 0.4M, 0.6M, 0.8M, and 1.0M. 2. Slice your apple in such a way that you can create sections of apple that are exactly 1.0cm x 1.0cm x 3.0cm (and do not contain any skin). If necessary, your teacher will sketch pictures on the board to explain further. 3. You will need 3 sections of apple in each of the 6 experimental beakers. 4. Keep each set of three apple sections in a covered beaker until it is your turn to use the balance. 5. Determine the mass of each of the three sections together and record the data in Table 1.4. Place the three sections into the appropriate beaker of sucrose solution. Repeat for each of the beakers. 6. Cover the beakers with plastic wrap to prevent evaporation. 7. Let the beakers stand overnight, 8. On Day 2, remove the three sections from the beakers and blot them gently on a paper towel and determine their total mass. When blotting, do not squeeze liquid out of them. 9. Record the final mass in Table 1.4. Calculate the percentage change in mass and record it in Table 1.4 also: Percent change in mass = Final Mass-Initial Mass X 100 Initial Mass Include a Calculations section within your results in which you will show the formula (above) you used to calculate the percent change. No further calculations need to be shown. 10. Record the class Percent change in mass in Table Construct a graph of the percent change in mass at each of the molar concentrations of sucrose for your group s apple variety and the class average for both apple varieties all on the same axes. (3 sets of data) Analysis (answer in your data book): Follow the hand-written lab report protocol, and include the following questions and answers: Discussion Questions: 1. Compare your group s data with the data from the other apple varieties. (1 point) 2. Using the class average graph, predict the result of placing a typical apple section in a 0.3M sucrose solution. (1 point) 3. Using the class average graph, predict the result of placing a typical apple section in a 0.7M sucrose solution. (1 point) 4. What is the molar concentration of the solutes in each of the apple varieties studied by the class lab groups? (6 points) 5. Evaluate error in your group s investigation. (1 point) 6. How would you improve the investigation? (1 point)

3 This observational lab will be hand-written in your data book AP Osmosis Lab Part D: Onion Cell Plasmolysis Purpose: How do plant cells respond to hypertonic solutions? This is an observational lab and will not need a hypothesis Materials: Onion epidermis Compound microscope and wet slide supplies 15% NaCl solution in dropper bottles paper towel pieces Procedure 1. Prepare a wet mount of a small piece of the epidermis of an onion. You ll find an easy to separate layer on the inside of an onion scale. Break the leaf away from you and the epidermis will be easy to see. 2. Observe the cells near the edge under high power. Sketch and describe the appearance (using the Sheldon Science Sketch Criteria ). Do not continue until you can spot the cell membrane and nucleus, and be able to describe the location of the vacuole. 3. Add 2 or 3 drops of 15% NaCl to one edge. Draw the salt solution across the slide by touching a piece of paper towel to the fluid under the opposite edge of the cover slip. Observe the cells while you do this; you might need to wait a bit before the changes become obvious. Make a second sketch and describe the the onion cells. Explain what has happened. 4. Remove the cover slip and flood the onion epidermis with fresh water. Put the cover slip back on and observe, make a third sketch, describe and explain what has happened. Discussion Questions: 1. Plants often die next to roads that have been salted in the winter to remove ice. Explain why this happens. 2. Why don t plants have contractile vacuoles?

4 Name Date This part of the lab is mostly reading. The few written portions are to be hand-written in your data book Part E: Understanding Water Potential AP Osmosis Lab

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7 See also pp of Urry text.