BIO201 Lab 4

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Lab 4 Diffusion and Osmosis BIO201L Student Name: Alexandria Kershaw Access Code (located on the lid of your lab kit): AC-26K0QS Lab Report Format Expectations Utilize college level grammar and professional formatting when completing this worksheet. Submissions without proper formatting, all required photos or sufficient responses will be rejected. Pre- lab Questions 1. Define the following terms. a. hypertonic solution: A hypertonic solution has a higher concentration of solute in the solution on the outside of the permeable membrane than the concentration inside the membrane b. hypotonic solution: A hypotonic solution has a lower concentration of solute in the solution on the outside of the permeable membrane than the concentration inside the membrane c. isotonic solution: An isotonic solution has an equal concentration of solute in the solution on the outside of the permeable membrane as the concentration inside the membrane 2. Define osmotic pressure. Osmotic pressure, also called pressure potential, is the force required to prevent osmosis. It is defined as the tendency of a solution to lose water across an ideal, partially permeable membrane. 3. Explain what would happen to a cell placed in a hypertonic solution. A cell placed in a hypertonic solution would cause water molecules to move out of the cell, resulting in a shrunken/collapsed/crenated cell.

Lab 4 Diffusion and Osmosis BIO201L EXPERIMENT 1: DIFFUSION THROUGH A LIQUID Introduction Questions 1. State the molecular weight of the blue dye in grams per mole. 793 g/mole 2. State the molecular weight of the red dye in grams per mole. 496 g/mole 3. Why does this experiment require two dyes of different molecular weights? Answer this question, ensuring you explain the purpose of these two dyes in relation to the experiment. This experiment demonstrates the effect that different molecular weights have on the ability of dye to travel through a viscous medium.

Lab 4 Diffusion and Osmosis BIO201L Data and Observations Record the diameters you observed for both dyes in the table below. Table 1: Rate of Diffusion in Corn Syrup Time (sec) Blue Dye Red Dye 10 5mm 15mm 20 6mm 20mm 30 7.5mm 25mm 40 10mm 30mm 50 13mm 32mm 60 15mm 35mm 70 16mm 38mm 80 17.5m 40mm 90 18mm 42mm 100 20mm 43mm 110 20mm 45mm 120 21mm 47mm Calculate the speed of diffusion and present this, along with the required data, for both dyes below in Table 2. To calculate the hourly diffusion rate, multiply the total distance diffused by 30 . Table 2: Speed of Diffusion of Different Molecular Weight Dyes Structure Molecular Weight Total Distance Traveled (mm) Speed of Diffusion (mm/hr)* Blue Dye 793 g/mole 21mm 630mm/hr Red Dye 496 g/mole 47mm 1410mm/hr

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Lab 4 Diffusion and Osmosis BIO201L Results and Discussion 1. Examine the plot below. How well does it match the data you took in Table 1? My diameter in millimeter measurements ended much higher than these plots show. The data points themselves don’t match very well to mine, but the rates were similar in that red was about twice as fast as blue. 2. Which dye diffused the fastest? Red 3. How does the rate of diffusion correspond with the molecular weight of the dye? The lower the molecular weight of the dye, the faster the rate of diffusion. Inversely, the higher the molecular weight of the dye, the slower the rate of diffusion. 4. Does the rate of diffusion change over time? Why or why not? Yes, the rate of diffusion changes over time. As the concentration on either side of the membrane gets closer to equilibrium, the rate of diffusion slows and when equilibrium is reached, diffusion stops. EXPERIMENT 2: DIFFUSION - CONCENTRATION GRADIENTS AND MEMBRANE PERMEABILITY Introduction Questions

Lab 4 Diffusion and Osmosis BIO201L 1. What is the purpose of Step 5 in this experiment? Step 5 sets up a positive control for this experiment. 2. Why is it necessary to have positive and negative controls in this experiment? Positive and negative controls are necessary in this experiment to have a clear visual of what indicates the presence of glucose, and what the absence of glucose looks like; these serve as comparisons to interpret the results of experimental beaker. 3. What is the importance of Step 16 in the procedure? Step 16 tests for the presence of starch in the beaker water of the experimental beaker. This is important in indicating whether or not the starch diffused out of the dialysis bag after an hour of submersion. Data and Observations Record your observations of Steps 5 and 6 below. These values will be used to interpret your results. Table 3: Indicator Reagent Data Indicator Starch Positive Control (Color) Starch Negative Control (Color) Glucose Positive Control (Color) Glucose Negative Control (Color) Glucose Test Strip n/a n/a Brownish Green Light Teal IKI Dark Green/ Blackish Amber n/a n/a Record your observations from Steps 13 through 16 below. Table 4: Diffusion of Starch and Glucose Over Time Indicator Dialysis Bag After 1 Hour Beaker Water After 1 Hour Glucose Test Strip Brownish Green- Positive Light Green- Positive IKI Dark Green/Blackish- Positive Amber- Negative

Lab 4 Diffusion and Osmosis BIO201L Results and Discussion 1. Which substance(s) crossed the dialysis membrane? Support your response with data-based evidence. Only the glucose crossed the dialysis membrane into the beaker water. This is evident by the presence of glucose in the beaker water after one hour being submerged with a tight seal. 2. Which molecules remained inside of the dialysis bag? The starch molecules remained inside the dialysis bag. 3. Did all of the molecules diffuse out of the bag into the beaker? Why or why not? No, not all of the molecules diffused out of the bag into the beaker. The glucose was small enough to diffuse across the membrane and into the beaker, however, the starch molecules were too large to diffuse across it and remained only inside the dialysis bag itself.

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Lab 4 Diffusion and Osmosis BIO201L EXPERIMENT 3: OSMOSIS - DIRECTION AND CONCENTRATION GRADIENTS Introduction Questions 1. Before conducting the experiment, read through the steps to gain a full understanding of the experimental process involved. Then provide the hypothesis from Step 16 here. If the yellow and red bags have a higher concentration of sucrose inside their respective dialysis bag than the solution outside, then water will flow inside the bags. If the blue bag has the same concentration of sucrose as the solution outside, then there will be no net movement of water between the inside and outside of the blue dialysis bag. If the green bag has a lower concentration of sucrose than the solution outside, then water will flow out of the green dialysis bag. 2. Osmosis is how excess salts that accumulate in cells are transferred to the blood stream so they can be removed from the body. Explain how this process works in terms of tonicity. In terms of tonicity, an excess of salts accumulated in cells would cause the extracellular fluid to become hypotonic in comparison. Inversely, the cell has a greater concentration of salts and is hypertonic to the extracellular fluid. Since water in osmosis flows from hypotonic solutions to hypertonic solutions, water in the extracellular fluid flows into the cell. To prevent lysis of the cell, the excess salts are excreted to the blood stream. 3. How is this experiment similar to the way a cell membrane works in the body? How is it different? Be specific with your response. This experiment demonstrates the way water flows through membranes via osmosis, similar to how cells in the body experience osmosis. While this experiment only demonstrated water movement by passive transport, the cell membrane in the body requires energy for diffusion and active transport of solutes other than water. Data and Observations Record the observed volumes from Steps 14 and 19 below. Also calculate the net displacement. Table 6: Sucrose Concentration vs. Tubing Permeability Band Color Sucrose % Initial Volume (mL) Final Volume (mL) Net Displacement (mL) Yellow 30 10 12 2 Red 15 10 11 1 Blue 3 10 10 0 Green 3 10 8 2

Lab 4 Diffusion and Osmosis BIO201L Results and Discussion 1. For each of the tubing pieces, identify whether the solution inside was hypotonic, hypertonic, or isotonic in comparison to the beaker solution it was placed in. Yellow: Hypertonic to beaker; Red: Hypertonic to beaker; Blue: Isotonic to beaker; Green: Hypotonic to beaker 2. Which tubing increased the most in volume? Why? The yellow tube increased the most in volume because it was hypertonic placed in a hypotonic solution, and had the biggest difference between concentrations on either side of the membrane. 3. What does this tell you about the relative tonicity between the contents of the tubing and the solution in the beaker? The yellow and red bags contained a hypertonic solution relative to the hypotonic solution in which they were placed. The contents of the blue bag were isotonic relative to the solution in which it was placed. The green bag contained a hypotonic solution relative to the hypertonic solution in which it was placed. 4. What would happen if the tubing with the yellow band was placed in a beaker of distilled water? Water would move from the beaker through the membrane and into the yellow bag. 5. If you wanted water to flow out of a tubing piece filled with a 50% solution, what would the minimum concentration of the beaker solution need to be? Explain your answer using scientific evidence. In order for water to leave a piece of tubing which contains a 50% solution, the solution in which it is placed must be greater than 50%; this is because water flows from areas of lower concentration of solute to areas of higher concentration of solute. If using whole numbers to give a percentage, the minimum concentration of the beaker solution needs to be 51%; if using significant figures to give a percentage, the minimum concentration of the beaker solution needs to be 60%.

Lab 4 Diffusion and Osmosis BIO201L EXPERIMENT 4: OSMOSIS - TONICITY AND THE PLANT CELL Introduction Questions 1. Can all cells generate osmotic pressure? If not, which ones are able to do this? Not all cells can generate osmotic pressure. Plant cells are able to generate osmotic pressure. 2. What specialized structure do some cells utilize to generate osmotic pressure? Plant cells utilize their cell walls to generate osmotic pressure. Data and Observations Record your observations from the experiment in the table below. Also calculate the net displacement. Table 7: Water Displacement per Potato Sample Potato Potato Type and Observations Sample Initial Displacement (mL) Final Displacement (mL) Net Displacement (mL) 1 Gold Potato: pale yellow color inside, flexible, sort of rough texture 1A 11 12 1 1 Gold Potato: pale yellow color inside, flexible, sort of rough texture 1B 8 7.5 -0.5 2 Sweet Potato: bright orange color inside, stiff, rougher texture 2A 8 9 1 2 Sweet Potato: bright orange color inside, stiff, rougher texture 2B 6 5.5 -0.5

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Lab 4 Diffusion and Osmosis BIO201L Results and Discussion 1. How did the physical characteristics of the potato vary before and after the experiment? Did it vary by potato type? The potatoes submerged in water got much more rigid after an hour and became a bit lighter/paler in color. The potatoes submerged in the sodium chloride solution became much softer and more flexible and a bit darker/browner in color. The differences in before and after didn’t vary by type of potato, but by type of solution in which they were placed. 2. What does the net change in the potato sample indicate? The net change in potato samples indicated that the potatoes submerged in water gained water, while the potatoes submerged in the sodium chloride lost water. 3. Different types of potatoes have varying natural sugar concentrations. Explain how this may influence the water potential of each type of potato. A higher concentration of sugar in a potato has a higher solute potential combined with a lower water potential. The more sugar a potato contains, the more capable its cells are of drawing in water from an outside hypotonic solution, which means more sugar in a potato means lower water potential. More sugar in a potato should cause more water to enter its cells. 4. Based on the data from this experiment, hypothesize which potato has the highest natural sugar concentration. Explain your reasoning. The data I measured in this experiment was consistent across both potato types. However, based on the rigidity of the potatoes before (and after) submersion, I hypothesize the sweet potato has a higher natural sugar concentration. 5. Did water flow in or out of the plant cells (potato cells) in each of the samples examined? How do you know this? Samples 1A and 2A: In- positive net displacement; Samples 1B and 2B: Out- negative net displacement. The direction in which their respective displacements moved, paired with the either expansion or wilting, respectively, indicates which way water moved between the potatoes and the respective solutions in which they were placed. 6. Would this experiment work with other plant cells? What about with animal cells? Why or why not? Yes, this experiment would work with other plant cells because they also have cell walls which make them more resistant to damage that could kill the cell. This experiment would not work with animal cells because they lack a cell wall and thus are not as protected from damage and would likely lyse if placed into a hypotonic solution. 7. From what you know of tonicity, what can you say about the plant cells and the solutions in the test tubes? The potatoes placed in water (1A,2A) were hypertonic to the water, so the water was hypotonic

Lab 4 Diffusion and Osmosis BIO201L to the potato cells. The potatoes placed in sodium chloride solution (1B,2B) were hypotonic to the solution, so the sodium chloride solution was hypertonic to the potato cells. 8. What do your results show about the concentration of the cytoplasm in the potato cells at the start of the experiment? At the beginning of this experiment, the concentration of the cytoplasm of the potato samples 1A and 2A was hypertonic to the water; the concentration of the cytoplasm of the potato samples 1B and 2B was hypotonic to the sodium chloride solution.