Diffusion and Osmosis

Diffusion and Osmosis PRE-LAB QUESTIONS 1. Compare and contrast diffusion and osmosis. - Osmosis is the process of solvent traveling from a dilute solution to a concentrated solution to equalize the concentration - Diffusion is the process of particles moving from an area of high concentration to an area of lower concentration to equalize the concentration - Both processes have an end goal of solution concentration equalization - Both processes involve moving from an area of high concentration to an area of lower concentration (in osmosis, the high concentration of water (the dilute) is the high concentration) - Osmosis commonly refers to water molecules, where diffusion can be any mixture 2. Draw a picture of a cell in isotonic, hypotonic, and hypertonic states. 3. Why don’t red blood cells swell or shrink in blood? - Red blood cells do not shrink or swell in blood because blood and the red blood cells are in an isotonic state 4. How do osmotic power plants work? Osmotic power plants capture energy through osmosis of fresh and salt water. When the salt water and fresh water are mixed energy is released. A process of pressure retarded osmosis (PRO) captures the released energy during separation. 5. Research the structures that protect plant and animal cells from damage resulting from osmotic pressure. Write a few paragraphs explaining what they are, how they work, and where they are located. The Osmotic pressure coming from the separation of water from a solution can potentially damage a cell. To prevent damage, both plant and animal cells have structures that protect them. Plant cells have a rigid cell wall. When water enters the cell, it is stored in a vesicle. This cell wall will then protect the cell from damage from expansion. Cellulose is in the cell wall, and helps to give the cells structure, and protection and regulates what is coming and going. The cell wall protects and supports the inner cell Animal cells in comparison do not have a cell wall. To reduce pressure, the cells use active transport. The cell membrane functions as a strong barrier between the cell and it’s outer surroundings. EXPERIMENT 1: DIFFUSION THROUGH A LIQUID Data Tables Table 1: Rate of Diffusion in Corn Syrup Time (sec) Blue Dye Red Dye 10 1.65 1.5 20 2.20 2.30 30 2.50 2.65 40 2.60 3 50 2.80 3.25 60 3 3.50 70 3.25 3.65 80 3.6 3.80 90 3.75 3.90 100 3.85 3.95 110 3.95 4.0 Time (sec) Blue Dye Red Dye 120 4.0 4.10 Initial position of blue 1.50 initial position of red 1.35 Table 2: Speed of Diffusion of Different Molecular Weight Dyes Structure Molecular Weight Total Distance Traveled (mm) Speed of Diffusion (mm/hr)* Blue Dye 793g/mole 2.4cm=24mm 720mm/hr Red Dye 496g/mole 2.75cm=27.5mm 825mm/hr *To get the hourly diffusion rate, multiply the total distance diffused by 30. Post-Lab Questions 1. Create a graph of your data from Table 1. Using a graphing program, such as Microsoft Excel®. If you do not have access to Microsoft Excel, use a free graphing program available online. (please note- the black line should not be considered; due to user error I was unable to remove the black line) 2. Examine the plot below. How well does it match the data you recorded in Table 1? a. The data and therefore line graphs look very similar, although my data ended with the two dyes being closer than the presented data. In my data, the red dye also ultimately diffused faster, but there was less of a difference in my data versus the presented data. 3. Which dye diffused faster? In my data, and the presented data, the red dye diffused faster than the blue dye. 4. Does the rate of diffusion correspond with the molecular weight of the dye? Yes, as shown by my data and the presented data, the lower the molecular the weight the faster the diffusion can go 5. Does the rate of diffusion change over time? Why or why not? Yes, the diffusion changes over time. For this experiment, the rate of diffusion was fastest in the beginning and then began to level off. Eventually the diffusion would halt. If the dye was left for several hours after the experimental two minutes, there may be more diffusion shown, but the results would not be significant. Eventually the solution will reach it’s maximum equilibrium. 6. Do you think your results would change if the corn syrup was replaced with water? Why or why not? Yes, I think if the corn syrup were replaced with water, the diffusion would happen faster because in the corn syrup there is a lower concentration on water than in pure water. EXPERIMENT 2: DIFFUSION – CONCENTRATION GRADIENTS AND MEMBRANE PERMEABILITY Data Tables Table 3: Indicator Reagent Data Indicator Starch Positive Control (Color) Glucose Test Strip n/a n/a Dark brownish/black IKI Starch Negative Control (Color) Light brown/orange Glucose Positive Control (Color) Glucose Negative Control (Color) Greenish Yellow n/a n/a Table 4: Diffusion of Starch and Glucose Over Time Indicator Glucose Test Strip IKI Dialysis Bag After 1 Hour Yellow Dark yellow/brown Beaker Water After 1 Hour Greenish Light brown/orange Post-Lab Questions 1. Why is it necessary to have positive and negative controls in this experiment? Positive and negative controls are necessary to ensure there is no other contributing factors leading to incorrect experiment results. Positive and negative controls allow us to confidently say our variable is making the change, not another factor. 2. Draw a diagram of the experimental setup. Use arrows to depict the movement of each substance in the dialysis bag and the beaker. 3. Which substance(s) crossed the dialysis membrane? Support your response with databased evidence. Water and glucose crossed the membrane. The data supports this claim, because of the change in color and the water testing positive for glucose, but the beaker water nor reacting to the iodine 4. Which molecules remained inside of the dialysis bag? The molecules that remained inside of the bag were the starch. This was indicated by the dialysis bag contents turned dark brown. 5. Did all of the molecules diffuse out of the bag into the beaker? Why or why not? No, from my experimental findings, the starch did not leave the bag EXPERIMENT 3: OSMOSIS – DIRECTION AND CONCENTRATION GRADIENTS My hypothesis is that the yellow bag with the highest concentration of sucrose will increase in volume due to osmosis Scientific reasoning is through osmosis. Osmosis tells the water to go from an area of high concentration of water to an area of lower concentration of water/higher concentration of the solute. Data Tables Table 6: Sucrose Concentration vs. Tubing Permeability Band Color Sucrose % Initial Volume (mL) Final Volume (mL) Net Displacement (mL) Yellow 30 9.5mL 11.25mL 1.75mL Red 15 9mL 9.75mL 0.75mL Blue 3 10.25mL 9.80mL -0.45mL Green 3 10mL 7.5mL -2.5mL Post-Lab Questions 6. For each dialysis bag, identify whether the solution inside was hypotonic, hypertonic, or isotonic in comparison to the beaker it was placed in. - Yellow – hypotonic beaker solution, hypertonic dialysis bag - Red- hypotonic beaker solution, hypertonic dialysis bag - Blue- hypertonic beaker solution, hypotonic dialysis bag - Green- hypertonic beaker solution, hypotonic dialysis bag 7. Which dialysis bag increased the most in volume? Why? In my experiment, the yellow increased the most in volume, because the net displacement was the highest for the yellow tube. 8. What does this tell you about the relative tonicity between the contents of the tubing and the solution in the beaker? The increase in volume of the yellow banded tube tells me the tonicity is high as the composition of the solvent and solution allows for a large gradient difference causing the increase in volume of the yellow tubing 9. What would happen if the tubing with the yellow rubber band was placed in a beaker of distilled water? If the yellow banded tubing was placed in distilled water instead of the 3% sucrose, the tubing would expand more, because the distilled water would have a higher concentration of water than the sucrose solution increasing the water move into the tubing through osmosis 10. Suppose you had a 90% sucrose solution in one of the beakers instead of a 3% sucrose solution. How might this change your results? If there was a 90% sucrose solution instead of the 3% solution, the yellow tube would decrease in volume to try to meet equilibrium between the solutions. 11. Describe the similarities and differences between the dialysis bag and a cell membrane. Be specific. In this experiment, the tubing acted as the cell membrane. Both act as a semipermeable membrane. This membrane/tubing selectively allows molecules to pass through it. The difference between the two, is that the membrane is found naturally in cells, and the dialysis tubing is manmade and not naturally occurring 12. If you want water to flow out of a dialysis bag filled with a 50% sucrose solution, what would the minimum concentration of the beaker solution need to be? If I wanted to make a condition in which water would flow out of a dialysis bag that had a 50% sucrose solution inside of it, the beaker would need to be a concentration of at 49% or less water. EXPERIMENT 4: OSMOSIS – TONICITY AND THE PLANT CELL Data Tables Table 7: Water Displacement per Potato Sample Potato 1 1 2 2 Potato Type and Observations Russet Potato: skin matte looking, dirty feeling. Firm. Brown outside with patches of lighter areas Red Potato: Silkier outside, red skin. Smoother feeling, less “dirt” on the outside. Skin appears to have a dull shine. Sample Initial Displacement (mL) Final Displacement (mL) Net Displacement (mL) 1A 5.75 ml 5.85ml .10ml 1B 7.3 ml 7ml -.30ml 2A 6.75ml 7ml .25ml 2B 7.25ml 6ml -1.25ml Post-Lab Questions 1. How did the physical characteristics of the potatoes vary before and after the experiment? Did it vary by potato type? The physical characteristics varied by type of potato. The russet potato had a dull, brown appearance, whereas the red potato had a silkier finish with a red coloring. Both potatoes were easily identifiable as a potato. Both potatoes had a similar appearance before the experiment as they did after the experiment. Both potatoes appeared to be much less firm, and more bendable. 2. What does the net displacement change in the potato sample indicate? The net displacement in the potatoes presents the amount of the solution that has entered or left the potato. 3. Different types of potatoes have varying natural sugar concentrations. Explain how this may influence the water potential of the potato cells. The sugar concentrations of potatoes may influence water potential in potato cells. Knowing that diffusion is the process of moving from high to an area of low concentration, the higher the sugar concentration, the more water that will go in because of the need for equilibrium. If the sugar concentration is lower, water may diffuse out of the potato. 4. Based on the data from this experiment, hypothesize which potato has the highest natural sugar concentration. Explain your reasoning. Based on the data from this experiment, my hypothesis is that the red potato had more sugar than the russet potato. 5. Did water flow in or out of the plant (potato) cells? How do you know this? The solution went in and out the potato cells. I know this from the net displacement of the water for the potato. Some of the displacements were positive, and some was negative. 6. Would this experiment work with other plant cells? What about animal cells? Why or why not? Plant cells have a cell wall that protect and support the cell in hypotonic solutions. In contrast, animal cells do not have a cell wall to protect them, so when placed in a hypotonic solution, the cell expands and may burst/ Other plants cells would react similarly, and expand (without bursting) or shriveling. 7. From what you know of tonicity, what can you say about the plant cells and the solutions in the test tubes? The tonicity of the cells have different concentration gradients. Some solutions caused the potato to gain water (increasing net displacement) some solution caused the potato to lose water, decreasing the net displacement. The NaCl appeared to be a hypertonic, where the water appeared to be a hypotonic. 8. What do your results indicate about the concentration of the cytoplasm in the potato cells at the start of the experiment? My results indicate the NaCl solution made the potato shrivel, where the pure water caused the cells to expand, so the cytoplasm was less concentrated 9. If the potato is allowed to dehydrate by sitting in open air, would the cells absorb more or less water? Explain. I believe the cells would be able to absorb less water after they were dehydrated, because as the water decreased causing dehydration, the concentration would increase which would reduce the osmotic pressure potential