Diffusion Osmosis Dialysis Lab

 

Anthony Araracap Period 4 AP Biology Diffusion & Osmosis Dialysis Lab Background: Diffusion: The spontaneous movement of molecules or particles p articles in solution along a concentration gradient (i.e. from areas of high concentration to a low concentration) until there is an equilibrium. Osmosis: The diffusion of water molecules through a selectively permeable membrane from a region of low solute concentration co ncentration to a region of high solute concentration. Equilibrium: A condition in which all influences acting upon it are canceled by others, resulting in a stable, balanced, or unchanging system. Selectively Permeable Membrane: A membrane that allows only certain materials to pass through it by diffusion. Hypotonic: A condition in which the inside of the animal or plant cell has a higher  solute concentration than its environment. Osmosis causes a net flow of water into the cell, causing swelling and expansion. This swelling may cause cells without a rigid cell wall to burst. Hypertonic: A condition in which the environment has a higher solute concentration than inside the animal or plant cell. Osmosis pressure causes water to flow out of the cells and causing the cell to shrink. Isotonic: A solution of equal solute concentration that has no net flow of water  across the selectively permeable membrane. Water Potential: The physical property predicting the direction in which water will flow, governed by solute concentration and applied pressure; the potential energy of  water to move. Osmotic Potential(solute potential): The potential for water to move across a selectively  permeable membrane, where the osmotic potential of pure pu re water is 0 and any water movement is measured with a negative value. Pressure Potential: The physical pressure on a solution Osmotic Pressure: Theseparated pressure from that must be exerted a solution containing a given concentration of solute a sample of the on pure solvent by a membrane. Purpose: The purpose of the lab was to conduct an experiment and observe the types of   passive transport, namely diffusion and osmosis. The experiment will show how molecules in a solution are able to move from an area of high concentration to an area of low concentration. It will also show us how hypertonic and hypotonic solutions exist, as well as how cells try to get  back into an isotonic state. In doing do ing so, this lab will allow us to learn wh why y and how diffusion and osmosis happens in all living things. We will be testing the movement of solutes from areas of  high concentration to the area of lower concentration that surrounds them.

 

Hypothesis: Part A) I think molecules of starch and glucose will enter the water in the beaker. Part B) I think osmosis will occur and try to make each solution isotonic. Part C) I think the water potential of the potato will be negative. Part D) I think the salt will make the cell become hypertonic. Materials: ● Dialysis tubing ● Distilled water  ● Starch solution ● Glucose solutions ● Potatoes(sweet and regular) ● String ● Beakers ● Starch solution ● Iodine solution ● Stopwatch ● knife Procedure: Part A) 1)Obtain a dialysis tubing that has been submerged in water. Tie off an end to form a  bag. 2)Test the solution for a presence of glucose. g lucose. 3)Place a starch solution into the bag. 4)Fill a cup 2/3 full of water and add a solution to the water. Record the color  change of the solution and amount of glucose present. 5)Immerse the bag into the beaker of solution. 6)Wait 30 minutes or until a distinct color change has taken place in both the bag and solution. 7)Test the liquid remaining in the beaker for any presence of glucose. Part B) 1)Obtain 6 strips of presoaked dialysis tubing. 2)Tie a knot in one end of each piece of tubing to form 6 bags. Fill them each up with different solutions. 3)Rinse and record weight of each bag. 4)Place each bag into a beaker to find the molarity of the solution in the dialysis bags. 5)Now fill each beaker with 2/3 of water or enough to completely submerge the bag. 6)After 30 minutes, remove bags from water and determine their mass. Part C) 1) Pour 100 ml of the assigned liquid into a labeled 250 ml beaker.

 

2) Use a cork borer to cut four potato cylinders. cylinders. Cut each cylinder to approximately approximately 3 cm in length. Do not include any skin on the cylinders. 3) Determine and record the initial mass (grams) of the four potato cylinders. 4)Place the cylinders in your beaker and cover with plastic wrap to prevent evaporation. Let stand overnight. 5) Remove the the cylinders from the beaker. Blot dry and weigh. Record the final mass. 6) (Do the same for sweet potatoes) Part D) 1)Prepare a wet mount slide of an epidermis of an onion. Observe and record what you see. 2)Add a few drops of a salt solution across the slide. Sketch and describe the onion cell. 3)Remove the cover slip and flood the onion cell with water. Observe and describe what happened to the cellData & Observations: Part A. Data table (Diffusion) Color Color Time Dialysis Bag Beaker Start Cloudy white Yellow brown 30min Light blue near   Cloudy

Glucose Content Dialysis Yes Yes

Glucose Content Beaker   No Yes

top, cloudy white yellow/orange at bottom Part B. Data table (Osmosis) Solution Dialysis Bag Initial Dialysis Bag Final Mass(g) Mass(g) Water 10.4g 11.9g 0.2M 4.8g 8.1g 0.4M 12.3g 15.2g 0.6M 11.9g 15.6g 0.8M 12.1g 12.1g 1.0 M 4.7g 16.8g ?M

11.4g

15.9g

Change in in Mass(g) Mass(g) % Change Change in Mass Mass 1.5g 3.3g 2.9g 3.7g 0g 12.1g

14.4% 40% 23.6% 31.1% 0% 257.4%

4.5g

39.4%

Analysis: Part A) 1) Glucose is leaving the bag and the IKI is entering the bag. The change in the color of  the bag proves IKI is entering the bag and after testing the beaker, we found there to be glucose, which proves that glucose was leaving the bag and entering the beaker of H2O and IKI. 2) In the results, the IKI moved from the beaker to the bag. This caused the change in the color of the bag. The IKI moved into the bag to make the concentrations outside the  bag equal to inside the bag. The glucose solution moved out of the bag. The glucose moved to make the solute concentration inside and outside the bag equal. 3) (See graph) 4) Water molecules, IKI molecules, Glucose molecules, and Membrane Pores. Starch

 

molecules are too large to enter or exit through the holes of the dialysis tubing. 5) If the experiment started with glucose and IKI inside the bag with H2O and starch in the beaker, the glucose and IKI would move out of the bag to make the concentrations equal, changing the color of the solution within the beaker, the starch, however, could not move into the bag because its molecules are too large to pass through the semi permeable membrane of the dialysis tubing. 6) In order to open the dialysis tubes easily and give assurance that the tubes were clean. 7) Sucrose is a larger molecule than glucose, meaning that the dialysis tubing would not  be able to pass into the dialysis bag. 8) The test was necessary in order to see if glucose was found in the beaker. Part B) 1) The molarity of the sucrose in the bag determines the amount of water that either  moves into or out of the bag, which in turn, changes the mass. For example, when the  bag contained a 0.2M solution, water entered the bag to make the concentrations inside and outside of the bag more equal. As this happened, the mass rose by 0.9 grams, a 4.2  percent increase. 2) The bag will expand will submerged in the solution, thus space is needed for  expansion. 3) The percent change in mass was calculated to show how much the mass increased due to the addition of o f water, which was trying to equal the con concentrations centrations in both the  bags and the cups. 4) If each of the bags b ags were placed into a 0 0.4M .4M solution instead of distilled water, the masses of the bags would have changed in different ways. The mass of the bags filled with distilled water and 0.2M sucrose would have gone down because water would have left the bag. The mass of the 0.4M bag would have stayed the same because the concentrations are now equal. The masses of the 0.6M, 0.8M, and 1.0M bags would have increased because water would have moved into the bag to equalize the concentrations. Part C) 1) (See graph) 2) ψ =(-1)(.55M)(0.0831K)(295K)/(L) =(-1)(.55M)(0.0831K)(295K)/(L)(M*K) (M*K) = -8.6bars for regular potatoes  

Osmotic Pressure= -8.6bars 3) The water potential of the potato core after dehydrating will decrease because the water within the potato would evaporate and therefore lower the water potential. 4) If a plant cell has a lower water potential than its surrounding environment and if   pressure is equal to zero, the cell hypertonic to its environment and will gain water. Since the surrounding environment or the hypotonic solution has a higher water   potential, the net movement of water will be from the hypotonic solution to the hypertonic solution, in this case, plant cells. 5) This technique works since it keeps plants turgid, since leaving the produce out in the open causes dehydration spraying them would keep them hydrated. 6) If too much fertilizer is added, the plants will wilt due to the cells becoming hypertonic and shriveling up. 7) The ? M sucrose solution was said to be 0.5 M sucrose solution.

 

Error Analysis: During this lab, several errors may have occurred. For example, while weighing the  potatoes and bags, the cover may have been on, thus giving a lower mass than expected. Also, the dialysis bags may not have been fully tied together, thus allowing solution to get into the bag without having to penetrate the membrane. Another error that may have occurred was not completely drying the dialysis bag, giving a heavier result than should have been recorded. Besides these errors, fairly accurate data would have been retrieved. Discussion: During this lab, we observed passive transport, both diffusion and osmosis. The hypothesis for part A was disproven, since starch molecules cannot diffuse out of the bag and into the water surrounding it since they were far too large to exit though the semi-permeable dialysis tubing. The hypothesis for part B was proven correct. We witnessed how the bags got heavier after 30 minutes, indicating water had diffused into the bag to try and make them isotonic with their surrounding environment. Alongside this, the hypothesis for part C was  proven correct as well: the water potential for the potato was negative; indicating water  movement towards the potatoes was high. The hypothesis for part D was also correct. Once salt was added to the onion, it showed how the cells became hypertonic and shriveled up, but as soon as water hit them, they grew right back up and became turgid once again. Discussion Questions: (None indicated)