Possible Practical Investigation to demonstrate Diffusion / Osmosis Diffusion, Osmosis Investigation Aim To become more familiar with Diffusion and Osmosis by investigating the movement of molecules of varying size through a simulated semi permeable membrane at differing temperatures. Write hypotheses that demonstrate an educated guess as to the outcome of this practical investigation. Use these questions to help you formulate your hypotheses; 1. Looking at the fluid in the dialysing tube (a glucose and starch solution) will either or both molecules diffuse out of the dialysing bag? 2. If a molecule does diffuse out of the dialysing tube into the distilled water at which temperature do you expect this to happen fastest? 3. If molecules do not leave the dialysing tube what do you expect to happen to the level of water in the thistle funnel.

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Retort stand and clamp Thistle funnel Gas jar Dialysing tubing (cellulose) – 20 – 25 cm Rubber bands Thermometer Room temperature Distilled water 20 degrees C Distilled water heated to 40 degree C Ice made from distilled water Glass marking pen Glucose and Starch solution Iodine/Potassium Iodide solution Testape Stopwatch

Method Students are to work in pairs and three pairs are to work together forming a group of six. Each pair will be responsible for the set up of one set of equipment. Their set up should be dialysing tubing containing glucose and starch solution that will be placed into a gas jar containing one of three possible temperatures of distilled water. (i) Room temperature distilled water (20۫C) in the gas jar OR 40۫C distilled water in the gas jar OR Distilled water with ice (the temperature of this should be determined and recorded) water in the gas jar. Each pair of students is to set up a retort stand and clamp. Next they are to seal up a piece of dialysis tubing very tightly at one end with a rubber band. They are to then, very carefully open the dialysing tubing, gently insert the thistle funnel and then make another tight seal with another rubber band. Very carefully fill the dialysing tube via the thistle funnel with the glucose and starch solution, making sure you do not spill any onto the outside of the thistle funnel or dialysing tubing. Continue this until the dialysing tube is filled to just above the rubber band on the top of the dialysing tubing. Using a glass marking pen put a line to indicate the height of the glucose and starch solution in the thistle funnel. Gently attach the clamp below the thistle funnel and put it high enough up, that the gas jar when ready can be placed below and the dialysing tube containing the glucose and starch solution can be lowered into the distilled water. Next each pair of students is to fill the gas jar 2/3 with the appropriate temperature of distilled water and then dip a piece of testape into the water. Check the result of the testape against the colour chart. 1. Is there any glucose present in the distilled water in the gas jar? Add Iodine/Potassium iodide solution to the appropriate distilled water until the water is brownish in colour (about 10mls or 20 drops from a dropping bottle.) Retest with testape. 2. Is there any glucose in the distilled water/iodine/potassium iodide solution? One student gently lower the dialysing tube into the distilled water, the other student immediately starts the stop watch and retests the water with Testape. 3. Is there any glucose in the gas jar? Test the water with Testape every minute for 15 minutes. Record your results. Also look at the dialysing bag and see if you notice any change in colour within the bag? Record any changes and the time. 4. After 15 minutes is there any glucose in the gas jar? 5. If there is, explain how this has occurred. 6. Were there any changes in the colour of the solution in the dialysing bag? Explain any changes you may have seen. 7. Were the results the same for all three set ups for your group? If there were any differences explain why they were different?

Leave the equipment until the end of the class, take the temperature of the three distilled waters, recheck each with testape as well as look for any colour change in the solution in the dialysing tube or any change in the height of the fluid in the thistle funnel . Record your results.

Conclusions 8. Explain your results in terms of diffusion or Osmosis for each of: a. Changes in testape reading; b. Colour change in solution in the dialysing tube c. Any change in height of the fluid in the thistle funnel. 9. What effect has temperature had the processes of Diffusion and Osmosis. 10. Were your hypothesis supported or negated. Explain

Other Osmosis Investigations Egg Osmosis In Biological systems the most common solvent is water. Diffusion is the net movement of solute molecules from regions where they are in high concentrations (large numbers of molecules) to regions where they are in low concentration (smaller numbers of molecules) until they are evenly distributed. The solvent molecules are also moving, so they diffuse from where they are in relatively high numbers (in the region located away from where the solute has been added) and they move towards areas where there are now in relatively low numbers of solvent molecules (due to the addition of the solute to these areas). The random motion of the solute and solvent towards each other will eventually result in an even distribution of molecules within the space. A semi permeable membrane is one that will allow small molecules such as water molecules or the solvent molecules to pass through, but the larger solute molecules are unable to pass through. This can create an imbalance of solute concentration on either side of the membrane. Solvent molecules pass freely from one side of the membrane to the other, however, the solute molecules are prevented from doing this and so diffusion of solute molecules across the membrane to equalise the concentrations cannot occur. As the solvent molecules can still diffuse, they will move to the side of the membrane where the solute is in highest concentration, as that is where there will be comparatively fewer water or solvent molecules. This special case of diffusion is known as OSMOSIS, and refers to the movement of the solvent as the solute is unable to equalise.

Aim This activity is designed to investigate Osmosis using a membrane found around a hen’s egg to simulate what would happen to a cell when solute concentrations varied in the surrounding environment.

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1 raw egg 250 ml beaker Vinegar Measuring cylinder Spoon Paper towel Strong sucrose solution Distilled water Electronic balance Pin

Method 1. Use an electronic scale to weigh your egg and record your results. Gently put your egg into the beaker and cover with 200 mL of vinegar. Leave for a few days. 2. Use the spoon to gently remove the egg from the beaker. You will need to be very careful as the egg is extremely fragile now. Gently rinse the egg and roll gently on paper towel. Use the electronic balance to find the mass of the egg. Then use the measuring cylinder to measure the amount of vinegar left in the beaker. Record your findings. Rinse out the beaker. 3. Pour 200 mL of concentrated sucrose solution into the beaker and gently place the egg into the sucrose solution. Set the beaker and egg aside, just before the end of the lesson, check the egg and record any changes. 4. Next lesson again observe the egg and record any changes 5. Use the spoon to very carefully remove the egg from the beaker, it is even more fragile. Very gently, rinse and gently dry the egg and use the electronic balance and record its mass 6. Use the measuring cylinder, to measure the amount of sucrose solution in the beaker and record your results. Rinse out the beaker. 7. Pour 200 mL of water into the beaker and gently place the egg into the sucrose solution. Set the beaker and egg aside, just before the end of the lesson, check the egg and record any changes. 8. Next lesson again observe the egg and record any changes 9. Use the spoon to very carefully remove the egg from the beaker, it is even more fragile. Very gently, rinse and gently dry the egg and use the electronic balance and record its mass 10. Use the measuring cylinder, to measure the amount of solution in the beaker and record your results. Rinse out the beaker.

11. Put the egg on some paper towel and take a pin and gently prick the membrane. Record what happens. 12. When all results and observations are recorded, clean up equipment and dispose of the egg following your teacher’s instructions. Graph your results and describe the relationship reflected (compare the change in the egg’s mass as the type of liquid changed and show the change in the volume of the liquid as the egg was put into the different solutions)

Discussion 1. Explain the volume of liquid remaining when the egg was removed from the sucrose solution. 2. .When the egg was placed in the water, which direction did the water molecules move? Explain your answer. 3. Why do supermarkets and green grocers spray their fresh produce with water? 4. Why might you die if you drank salt water rather than fresh?. Explain. 5. If a bowl of fresh cherries are sprinkled with sugar and left for a while explain why they will be covered with juice.

Conclusion Explain what would happen to a cell in the following solutions in relation to osmosis: A strong salt solution (much higher than that found with in the cell) Distilled water Salt solution of the same concentration as the cell