LAB Potato Cores Honors Biology, Newton North High

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1 Name Date Block LAB Potato Cores Honors Biology, Newton North High BACKGROUND: Osmosis is a type of passive transport. No input of energy is needed in order for water to pass through a selectively permeable membrane. Osmosis is the diffusion of water across a membrane going down its concentration gradient. In other words, water will move from areas of high water concentration into areas of low water concentration. Once equilibrium is reached, molecules of water will continue to cross the membrane, moving in equal amounts back and forth. All cells depend on the process of osmosis to transport water. Plant cells, in particular, need lots of water to stay healthy. Plant cells depend on osmotic (water) pressure inside their central vacuole in order to grow tall and stand upright. The osmotic pressure inside a central vacuole is known as turgor pressure. OBJECTIVES:! To observe osmosis in a plant.! To determine the effects of varying concentrations of sugar water on plant cells. MATERIALS: 5 plastic cups & covers lab tray tape marker stirring rod distilled water large white potato borer electronic balance Sucrose solutions: 0.2M, 0.4M, 0.6M and 0.8M pipette metric ruler PROCEDURE: DAY #1 THE SET UP 1. Obtain 5 plastic cups, with a permanent marker label each with: a. your group s name and block. b. 0M sucrose, 0.2M sucrose, 0.4M sucrose, 0.6M sucrose and 0.8M sucrose. 2. Using a borer, core out 5 cylinders of potato. BE CAREFUL NOT TO HOLD THE POTATO IN YOUR HAND! Be sure to put the potato on the table when you use the borer. If the potato gets stuck in the borer, use a stirring rod to gently push out the potato. 3. Do not include any skin on the cylinders. Using a knife, square off both ends of all of the potato cylinders, cutting them so they are between 20 and 30 mm long. All five cylinders do not have to be of equal length. 4. Observe the texture on the potato cylinders. Record observations in the Data Table Using a metric ruler, measure the length of each potato cylinder to the nearest millimeter. Record the measurements in the Data Table 1. M. Rice & N. Berg, NNHS Page 1 of 5

2 6. Using an electronic balance, determine the initial mass of each potato cylinder. Record the mass in the Data Table Place each potato cylinder into its corresponding plastic cup. 8. Measure out *20-mL of each sucrose solution and pour into its corresponding plastic cup. *This amount may change depending on the size of the container. Pour enough solution to cover the potato cylinder in the cup. 9. Store the set up overnight according to your teacher s instructions. 10. Clean up your station. Wash the borer with soapy water in the sink. Wipe down the lab bench using a damp sponge. Return cleaned materials to your red tray. DAY #2 THE CLEAN UP 1. Carefully pour out the sucrose solutions from each plastic cup into the sink without dropping the potato cylinder down the drain! 2. Carefully observe the texture of each potato cylinder. Record observations in the Data Table 1. WARNING: Do not break the potato cylinders. When not handling your potato cylinders, be sure to place them back into their respective plastic cups. Do not let the potato cylinders sit on a paper towel for any long period of time. 3. Using an electronic balance, determine the final mass of each potato cylinder. Record the results in the Data Table Using a metric ruler, measure the final length of each potato cylinder to the nearest millimeter. Record the measurements in the Data Table Clean up your lab station. Place the potato cylinders and plastic cups into the trash. Take a damp sponge and wipe down your lab table. Return all other materials to your red tray. 6. RECORD your group data in the class data chart. 7. AFTER you are finish cleaning up your lab station, calculate the difference in mass and the percent change in mass according to the directions on page GRAPH the class data according to the directions on page 4. You can either do this graph by hand on the graph provided or on separate graph paper or you can do this graph on the computer and print out the graph. 9. TYPE your answers to the analysis questions. 10. STAPLE this lab, your graph, and your typed questions together to turn in. HONORS: LAB: Potato Cores Page 2 of 5

3 DATA TABLE 1. Group Observations Sucrose Solutions 0.0M Sucrose 0.2M Sucrose 0.4M Sucrose 0.6M Sucrose 0.8M Sucrose Initial Texture Final Texture Initial Length (mm) Final Length (mm) Initial Mass (g) Final Mass (g) CALCULATIONS: 1. Calculate the difference in mass. Record in Data Table 2. final mass initial mass = difference in mass 2. Calculate the percent change in mass. Record in Data Table 2. difference in mass x 100 initial mass = % change in mass DATA TABLE 2. Calculations Solution Concentration 0.0M Sucrose 0.2M Sucrose 0.4M Sucrose 0.6M Sucrose 0.8M Sucrose Difference in Mass (g) % Change in Mass HONORS: LAB: Potato Cores Page 3 of 5

4 DATA TABLE 3: Potato Core Results Class Data- Percent Change in Mass Solution Concentration 0.0M Sucrose Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Class Average 0.2M Sucrose 0.4M Sucrose 0.6M Sucrose 0.8M Sucrose GRAPHING CLASS DATA: 1. Use the class averages to create a line of best fit using the percent change in mass (g) versus the concentration of sucrose solution (M). Remember your title, labels, and units! HONORS: LAB: Potato Cores Page 4 of 5

5 ANALYSIS QUESTIONS: (Please TYPE) 1. Why did you calculate the percent change in mass rather than simply using the change in mass? 2. What is turgor pressure? Why is it important to a plant? 3. Which potato cylinder gained mass overnight? Explain how the potato cylinder gained mass. 4. Which potato cylinder lost mass? Explain how the potato cylinder lost mass. 5. a. Define isotonic. b. Use your first graph to estimate the percent sugar solution would be considered an isotonic solution. % sugar solution is an isotonic solution to the potato cores. c. Predict what would happen to the mass of the potato cores if they were placed into 1.0 M Sucrose. 6. A gardener accidentally watered his lawn with salt water instead of fresh water. a. Draw a labeled picture of what is happening to the plant cells in salt water. b. Describe what is happening inside the plant cells. HONORS: LAB: Potato Cores Page 5 of 5