Experiment 4 Osmosis Tonicity and the Plant Cell Plant cells are able to generate osmotic pressure while other cells cannot This is due to specialized plant structures such as the cell wall which prevent lysis caused by osmosis By taking advantage of this system you will be able to look at the effects of tonicity in a biological system Materials 16 g Sodium Chloride NaCl 4 Test Tubes 100 mL Graduated Cylinder 12 Pipettes Ruler Stopwatch Permanent Marker Test Tube Rack Water 2 Potatoes these must be different types e g russett Idaho sweet etc Knife sharp enough to cut a potato Cutting Board Procedure 1 Use the permanent marker to label two test tubes as A and two test tubes as B Place the test tubes in the test tube rack 2 Identify the two potato types in the first two cells of the first column in Table 7 Then select one potato to test first and record observations about the physical characteristics in Table 7 Note Be sure to include observations which acknowledge the texture color and any other distinguishing factors 3 Use a knife to carefully cut two strips of the potato on a cutting board These will be referred to as Sample A and Sample B The strips should be as close to 10 0 cm long and 1 0 cm wide as possible to ensure that the strips fit in the test tubes 4 Fill the 100 mL graduated cylinder with 50 mL of water Place the first potato strip Sample A into the graduated cylinder and record the initial displacement in Table 7 Note Displacement is a measurement of change It is calculated by subtracting the original volume 50 mL from the final volume after the potato is added to the 50 mL of water For example 57 mL 50 mL 7 mL of displacement 2013 eScience Labs LLC All Rights Reserved 5 Remove Sample A from the graduated cylinder and place it in Test Tube A If any water was lost in the graduated cylinder refill it to the 50 mL graduation mark 6 Place the second potato strip Sample B into the graduated cylinder Record the initial displacement in Table 7 7 Remove Sample B from the graduated cylinder and place it in Test Tube B If any water was lost in the graduated cylinder refill it to the 50 mL graduation mark 8 Repeat Steps 2 6 for the second potato type using the remaining test tubes in the test tube rack 9 Use a pipette to add water to each of the test tubes with the A samples in them until the water covers the potato strips 10 Refer to the instructions provided on the bottle with 16 g of sodium chloride in it to create a 20 sodium chloride solution Use a pipette to add the 20 sodium chloride solution to each of the test tubes with the B potato samples in them until the solution covers the potato strips 11 After an hour pour out the liquid from the test tubes 12 Repeat Steps 4 7 for each sample and type and record the final displacement values in Table 7 13 Complete the last column of Table 7 by subtracting the initial displacement from the final displacement Table 7 Water Displacement per Potato Sample Potato Type Russet Russet Idaho Idaho Potato Observations Dark brown rough dirty Dark brown rough dirty Light brown smoothish Light brown smoothish Sample A B A B Initial Final Displacement Net Displacement Displacement mL mL Step 11 mL 8 8 0 9 9 0 6 9 3 5 7 2 2013 eScience Labs LLC All Rights Reserved Post Lab Questions 1 How did the physical characteristics of the potato vary before and after the experiment Did it vary by potato type The color of the potatoes changed on some potatoes but not on the other potatoes 2 What does the net change in the potato sample indicate The net change represents the water movement in and out of the potatoes 3 Different types of potatoes have varying natural sugar concentrations Explain how this may influence the water potential of each type of potato The varying levels of sugar influence the water potential with each type of potato because it influences the water movement 4 Based on the data from this experiment hypothesize which potato has the highest natural sugar concentration Explain your reasoning If the potato has more sugar in it then it will absorb more water I came to this conclusion by looking at the data from my lab 5 Did water flow in or out of the plant cells potato cells in each of the samples examined How do you know this The water flowed into the potato on one of them but the water went out of the potato on the other sample 6 Would this experiment work with other plant cells What about with animal cells Why or why not The experiment would work but the results would be different Animal cells deal more with salt than sugar The experiments would have to be different The animal cells could even explode from taking in too much water 7 From what you know of tonicity what can you say about the plant cells and the solutions in the test tubes 2013 eScience Labs LLC All Rights Reserved If the potatoes have a higher concentration than the solution the water will move towards the potato but if the solution has a higher concentration it would do the opposite 8 What do your results show about the concentration of the cytoplasm in the potato cells at the start of the experiment The concentration of the cytoplasm in the potato cells 9 If the potato is allowed to dehydrate by sitting in open air would the potato cells be more likely to absorb more or less water Explain If the potato dehydrates it would be more likely to take in water This is because dehydration means without water and cells need water in them This would increase the likelihood of water absorption Although the higher concentration of water would be outside of the potato so it would not be moving to a higher concentration 2013 eScience Labs LLC All Rights Reserved