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Introduction: Atoms and molecules are the building blocks of cells. Both have kinetic energy and are constantly in motion. They continually bump into one another and bounce off into new directions. This action results in two important processes, diffusion and osmosis. Diffusion is the random movement of molecules from an area of higher concentration of those molecules to an area of lower concentration. Cells have selectively permeable membranes that only allow the movement of certain solutes. It allows oxygen and carbon dioxide exchange in the lungs and between the bodies of intracellular fluid and cells. Diffusion also aids in the transport of nutrients and water in the xylem and phloem of plants.
In those plants, it permits for the absorption of water into roots. An example of this process is the diffusion of a smell in a room. Eventually dynamic equilibrium will be reached. This means that the concentration of the molecules carrying the smell will be approximately equal through out the surrounding enclosed area and no net movement of the molecules will occur from one area to another. Osmosis is special kind of diffusion. It is the diffusion or movement of water through semi-permeable membranes from a region of higher water potential hypotonic solute to a region of lower water potential hypertonic solute. Water potential is the measure of free energy of water in a solution. There are three types of solutions. Isotonic solutions have an equal concentration of solute on both sides of the membrane, and dynamic equilibrium has been reached in the solution.
Hypertonic solutions have a higher concentration of solute on one side of the membrane than the other. Hypotonic solutions are the opposite of hypertonic solutions. A solute is what is being dissolved by the solvent water is the most common solvent in a solution. Water will always move from an area of higher water potential to an area of lower water potential. An important factor effecting of diffusion and osmosis is water potential. Water potential measures the tendency of water to leave one place in favor of another place. Water potential is affected by two physical factors. One factor is the addition of solute, which lowers the water potential. The other factor is pressure potential. An increase in pressure raised the water potential. The water potential of pure water at atmospheric pressure is defined as being zero.
The Greek letter psi is used to represent water potential. Plasmolysis is a phenomenon in walled plant cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall when the cell loses water to a hypertonic environment. This leads to a loss of turgor pressure the force directed against a cell wall after the influx of water and the swelling of a walled cell due to osmosis and eventual death of the plant. If water moves into the cell, the cell may lyse, or burst in animal cells, plant cells are equipped to handle large intakes of water. Water movement is directly proportional to the pressure on a system. Pressure potential is usually positive in living cells and negative in dead ones.
Diffusion and osmosis are not the only processes responsible for the movement of ions or molecules in an out of cells. Active transport is process that uses energy from ATP to move substances through the cell membrane. Normally, active transport moves a substance against its concentration gradient, that is to say from a region of low concentration to an area of higher concentration. Hypothesis: Osmosis and diffusion will continue until dynamic equilibrium is reached and net movement will no longer occur.
Diffusion is effected by the solute size and concen-tration gradient across a selectively permeable membrane. Water potential greatly determines the results in sections of the experiment. Exercise 1A For this exercise, the following materials are required: a 30 cm of 2. Exercise 1B This exercise of the experiment requires six strips of 30 cm dialysis tubing, ml beaker, 12 dialysis tubing clamps, funnel, six cups, distilled water, an electronic balance, timer, paper towels, and about 25 ml of each of these solutions: distilled water, 0.
For recording results, paper and pencil are necessary. Exercise 1C This part of the experiment requires a large potato, potato corer about 3 cm long , ml beaker, paper towels, scale, six cups, knife, paper, pencil and about ml of each of these solutions: distilled water, 0. Exercise 1D This section requires a calculator, paper, pencil, and graphing paper. Exercise 1A First, soak the dialysis tubing in distilled water for 24 hours. Before handling the tubing, wash dirty hands thoroughly to prevent getting oils on the dialysis tubing and changing the results.
Remove the tubing and tie off one end using the clamp. To use the clamp, twist the end of the bag several times and then fold it onto itself. Next, open the other end of the tubing by rubbing the end between two fingers. Use the glucose tape by dipping it into the solution. Record the color change of the tape and the color of the bag. Tie of the end with the tubing clamp. It is necessary to leave space for expansion but no air. Record the color change. Use glucose tap to test for any glucose in the water.
Record these results. Set the dialysis tubing in the beaker and let it sit for about 30 minutes. Remove the bag and record the change in water and bag color. Use the last two pieces of glucose tape to measure the glucose in the water and bag. Record results. Exercise 1B First, soak the dialysis tubing for about 24 hours. Again be sure to cleanse hands. Tie off one end of each tube with the clamps. Next, fill each tube with a different solution distilled water, 0. Weigh each bag separately on the electronic balance and record the masses. Soak the bags in separate cups filled with distilled water for about 30 minutes. Remove the bags and gently blot dry with paper towel. Reweigh, and record the mass. Exercise 1C First, slice the potato into to 3-cm discs. Use the potato corer to core out 24 cores. Weigh 4 cores together and record their mass. Fill each cup with one of the following solutions: distilled water, 0. In each cup put 4 potato cores, and allow them to sit over night.
Take out the cores and blot them dry. Again weigh them on the electronic scale. Record the change in mass. Calculate the information for the table. Compare the results with another group. Exercise 1D First, determine the solute potential of the glucose solution, the pressure potential, and the water potential. Graph the information given about the zucchini cores. Exercise 1E Prepare a wet mount slide of dyed onion skin. Observe under a light microscope and sketch how the cells appear. Add a few drops of the salt solution using a paper towel to wick the solution under the slip. Observe how the cells are effected and make another sketch.
Irvine Introduction: Because all molecules have kinetic energy and are constantly in motion cells go through a process called diffusion. Diffusion is the movement if molecules from an area of higher concentration to and area of lower concentration. This process with continue to occur until an equilibrium is reached. Osmosis is a different and unique kind of diffusion. Osmosis is the diffusion of water through a permeable membrane. In Osmosis water will travel from an area of higher water potential or an area of lower water potential. Hypothesis: I think that in this lab, osmosis and diffusion will occur between the solutions of different concentrations until a equilibrium is reached and there is no movement of water. M sucrose, 0. Tie off one end of the tubing to form a bag like structure. Through the open end of the bad, place the starch solution in to the bag. Tie off the other end of the bag to secure the substance inside. Make sure to record the color of the solution in Table 1.
Record the results in Table 1. Record the color of the solution in the Table 1. Put the bag in the cup full of the solution. Allow the bag and cup to stand over night. The next day record the final color of the solution in Table 1. Finally test the liquid in the cup and in the bag for the presence of glucose. Record the final results in Table 1. Pour 25mL of the six solutions into each of the six bags. Tie off the other end of the bags. Rinse each bag gently with distilled water and dry the outside of the bag with a paper towel. Put each of the six bags into the cups with the six different solutions. Let stand over night. The next day remove the bags from the water and carefully dry the bags with paper towel. Weigh each bag and record them in Table 1. Using a cork borer, cut the potato into 24 cylinders. Record the data in Table 1. Put 4 potato cores into each solution cup. Cover the cup with a lid to prevent evaporation. Let stand overnight.
Remove cores from the cup and dry them with a paper towel. Then determine there combined weigh in groups of 4 from the same cup. Calculate the percentages changes in mass. Collect the class data and determine the class change in mass. Then, graph the information that is given about the zucchini cores. Which substances are entering the bag and which are leaving the bag? What evidence supports the answer? Distilled water and IKI are leaving and entering. Glucose is able to leave the bag.
Explain the results that were obtained. Include the concentration differences and membrane pore size in the discussion. Glucose and small molecules were able to move through the pores. Water and IKI moved from high to low concentration. How could this experiment be modified so that quantitative data could be collected to show that water diffused into the dialysis bag? You could mass the bag before and after it is placed into the solution. Based on your observations, rank the following by relative size, beginning with the smallest: glucose molecules, water molecules, IKI molecules, membrane pores, and starch molecules. Water molecules, IKI molecules, Glucose molecules, membrane pores, and starch molecules. Explain the relationship between the change in mass and the molarity of sucrose within the dialysis bags.
The solute in hypertonic and water will move into the bag. As the molarity increases the water moves into the bag. Predict what would happen to the mass of each bag in the experiment of all the bags were places in a 0. With the 0. M bag, there will be no net movement of water because the solutions reach equilibrium. Why did you calculate the percent change in mass rather then simply using the change in mass? This was calculated because each group began with different initial masses and we would have different data.
All the groups need consistent data. A dialysis bag is filled with distilled water and then places in a sucrose solution. Calculate the percent change of mass, showing your calculations. The sucrose solution in the cup would have been hypotonic to the distilled water in the bag. If the potato core is allowed to dehydrate by sitting in the open air, would the water potential of the potato cells decrease or increase? It would decrease because the water would leave the cells and cause the water potential to go down. If a plant cell has a lower water potential then its surrounding environment and if pressure is equal to zero, is the cell hypertonic or hypotonic to its environment? Will the cell gain water or lose water?
It is hypotonic and it will gain water. The cup is open to the atmosphere, what is the pressure potential of the system? The pressure potential is zero. Where is the greatest water potential? In the dialysis bag. Water will diffuse out of the bag. It is because the water moves from the area of high water potential to an area of lower water potential. What effect does adding solute have on the solute potential component of the solution? It makes it more negative 7. Consider what would happen to a red blood sell placed in distilled water: A which would have the higher concentration of water molecules?
Distilled Water B which would have the higher water potential? Distilled Water C what would happen to the red blood cell? It would leak, because it would take to much water. Conclusion: In Exercise 1A the data collected helped tell which molecules can and can not move across a cell membrane. IKI, we know because of its color change, was able to move across a membrane. Starch, although, is too large to move across a membrane. Glucose was able to move freely, along with the water, across the cell membrane. In 1B, it was proven that water moves faster across the cell membrane then sucrose.
The water moved to help reach equilibrium between the 2 solutions. The sucrose molecules are too big to move across the membrane as fast as water can. In experiment 1C showed that the potatoes contained sucrose. The sucrose in the potato raised the solute potential, which lowered the water potential. The cup of distilled water had a high water potential water moves down the concentration gradient, causing the potato cores to take on water.
Observe the celery stick that was soaked in water. Record your observations. Break the celery stick that was soaked in water. Observe the celery stick that was soaked in saltwater. Break the celery stick that was soaked in saltwater. The chart below indicates a color scale of pH for phenolphthalein. The blocks are pink because the agar blocks were soaked in 0.
Obtain agar cubes in a plastic cup from your teacher. Be careful not to scratch any surface of the cubes. Using the metric ruler, measure the dimensions of each agar cube and record the measurements in your lab notebook. Place the three cubes carefully into a plastic cup. Add white vinegar acidic solution until the cubes are submerged. Using a plastic spoon, keep the cubes submerged for 10 minutes turning them frequently. As the cubes soak, calculate the surface area, volume, and surface area to volume ratio for each agar cube.
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