Part1A) For this lab we placed a solution of glucose and starch inside a dialysis tubing bag. We then placed this tube in a beaker containing water and potassium iodide. We wanted to determine whether or not the dialysis tubing bag was selectively permeable to the glucose and starch inside the tubing and the potassium iodide and water outside the bag.
Part1B) We wanted to determine the relationship between Molarity and percent change in mass for a dialysis tubing bag containing water and different concentrations of sucrose placed in a beaker of water.
Part1C) For this part of the lab, we wanted to determine the percent change in mass of potatoes when the potatoes were placed in a solutions of different sucrose concentrations. The reason we wanted to find the percent change in mass of potatoes is because we wanted to find the concentration of sucrose in the potatoes, and after finding the concentration of sucrose in the potatoes, we wanted to use this value to determine the solute potential of sucrose.
Part1E) We wanted to determine the osmosis taking place between an onion cell and a hypotonic, isotonic, and hypertonic solution in which the onion cell was placed.
Part1A) In this part of the lab, we tested the selective permeability of the dialysis tubing. When an objects membrane is selectively permeable, it only allows certain nutrients to pass through. This is largely determined by the size of the pores as well as the size of the objects that are trying to pass through the membrane.
Part1B) This next part of the lab tested for the ability of the dialysis bags to conduct osmosis. Osmosis is the passage of water through the selectively permeable membrane. The passage of water is crucial to all living things. However, too much water or too little water can be the differene between life and death. A human cell is isotonic. This means that there are equal amounts of water going in and out of the cell. The cell is in equilibrium and is functioning correctly. If a human cell receives too much water, it is in hypotonic state. The cell is bound to explode as the membrane cannot withstand the pressure exerted by the water. Conversely, the human cell can shrivel if too little water is present. In this situation, the cell is experiencing a hypertonic state where too little water is present to nourish it.
In plant cells, the cell wall is strong enough to withstand a hypotonic stage ands actually prefers having too much water than too little. In the hypotonic stage, the central vacuole is highly bloated and the plant stands upright. In the isotonic stage, the plant begins to wilt and droop as the cells do not have enough to hold them upright. In the hypertonic stage, the plant cells do not have enough water to sustain life and dry out and die.
Part1C) In this part of the lab, we tested the water potential in the potato cores by means of calculation. Water potential is waters tendency to move from a lower concentration of solute to a higher concentration of solute. The two factors that effect water potential is the sum of solute potential and pressure potential. So, there is a direct relationship between pressure potential and water potential. As water rushes into a cell, the pressure on the inside rises as well as on the outside in order to keep the cell from bursting. As pressure rises, the more water potential outside the cell. Solute potential is a little more ambiguous. Solute potential is always negative. Water travels towards higher concentration to evenly disperse the solution. Since there is less water in the solute, this decreases the water potential.
Part1E) In this part of the lab we looked at images of an onion cell in an isotonic, hypotonic and hypertonic solutions. Respectively, when a cell has equal amounts of water going in and out, too much water going in, and too little water. We looked at traces of plasmolysis. Plasmolysis is the shriveling and eventual death of a cell due to lack of water.
Part1A) We had to first create a dialysis bag by tieing off one end of dialysis tubing. In order to test what substances could or could not pass through the membrane of the dialysis bag, we had to first fill the dialysis bag with a solution of 15mL of 15% glucose and 1% starch. After filling the bag with the glucose and starch, we tied off the other end of the bag. We then obtained a 250mL beaker, and we filled the beaker with a solution of 250 mL water and 4mL of potassium iodide. In order to create a scenario of diffusion between the contents in the dialysis bag and the solution in the beaker, we had to place the dialysis bag in the beaker. After allowing the bag to remain in the environment of the water and potassium iodide solution for 30 minutes, we used a glucose indicator to test the solution inside and outside the bag for glucose.
Part1B) For this we had 6 dialysis bags and 6 beakers labeled: distiller water, .2M,.4M,.6M,.8M, and 1.0M for the different concentrations of sucrose. We followed the same method for making a dialysis bag out of dialysis tubing; filling each bag with a different concentration of sucrose, we made sure to leave enough room for the expansion of contents inside the bag when we tied the second end of the dialysis tubing. We filled the 250 mL beakers 2/3 filled with distilled water. Before placing each bag of sucrose solution into the corresponding beakers of distilled water, we took the mass of each bag using a gram scale. After allowing the bags to be submerged in their corresponding beakers for 30 minutes, we removed them and retook the bags' mass.
Part1C) First we placed differing concentrations of sucrose solution approximately 100mL in beakers. Next we took a potatoe and used a potatoe cork bearer to cut 24 cylindrical potatoe cores. We took the mass of 4 cores and placed them in a beaker. 4 cores per beaker. We covered the beakers with plastic wrapping after all cores were placed in their corresponding beakers to prevent evaporation. We let the beakers sit overnight and then we took the cores out and patted the cores with a paper towel to remove any water on the outside before placing them on the scale. The mass was retaken.
Part1E) Here we looked at images of onion cells that were soaked in isotonic, hypotonic and hypertonic solutions. We looked for the difference in structure as well as the appearance of the cell in the three different stages. We then analyzed the different pictures of the onion cell and the distinct attributes that go with the different stages.
Part1A) In this part of the lab we tested for the dialysis bags selective permeability. Our results showed that the dialysis bag is permeable to water, iodine, and glucose but not starch. Along with every other group, the contents (15% glucose 1%starch) were dyed blue to and the outside remained a yellow/orange. The blue indicated the presence of starch and the later test for glucose with the strips which was present in both inside and outside the bag. Every group concluded that the dialysis bag was semi permeable. It allowed starch, glucose and water to pass through while leaving starch in the bag. All groups agreed to these facts and test results. It was consistent with every group. This was the cleanest test of the entire class far as consistent data collection.
Even though the data for every group was the same, this lab could be improved. In order to ensure consistency, ever group should have the same amount of iodine, solution, and water. This would ensure consistent data collection.
Part1B) This part of the experiment tested the permeability of the dialysis bag as well as its ability to diffuse water. Our data relatively matches the class data with a few exceptions. The trend is relatively the same. As the molarity increases, so does the percent change in mass. The only difference in our data and the class average is that while the other groups averaged about the same (around the 10 range) our percent change was in the 25+ range. We believe this is caused by the amount of sucrose solution we put inside the dialysis bags in relation to other groups. We put in a lot more sucrose solution inside the bag which allowed more water to diffuse into the bag, increasing its mass. This could account for our changes in mass to be way higher than that of the class. However, our data still confirmed the trend as molarity increases, more water will diffuse across the bag to even out the molarity of both sides of the membrane. This experiment supports this trend.
Only change to this lab that would improve it is to have some form of measuring the amount of sucrose (i.e beaker) so the amount is the same for every bag. Then we can more accurately see the trend while maintaining data that doesn't range too far from group to group.
Part1C) Our data in this portion strayed lower than the class average yet there was an observable and consistent trend. There is an inverse relationship between the percent mass of the potato cores before and after the soak and the molarity of the substance. As molarity increased the % mass of the potato core decreased. The rest of the groups experienced the same trend. By the time the potato was soaked in the 1.0 M sucrose solution, there was a 22% decrease in mass on average. The data did eventually level out at the end. This wold account for the pressure potential. The class and our group saw this trend. The results support the fact that the higher the solute potential outside the potato, the more water potential there will be inside the cell which results in a loss if water and overall mass.
In order to improve this experiment, the amount, size and shape of the potato cores should have been the same for all tests. This would have resulted in more consistent and accurate data that would not range too far from group to group.
Part1E) This experiment was based off of the images we have in our reference below and our data/graphs section above. In this experiment we looked at images of the behavior of an onion cell when soaked in an isotonic, hypotonic, hypertonic solutions. We looked for evidence of plasmolysis. We found it in the picture of the hypertonic solution. The cell appears shriveled and less functional than the cell in the hypotonic solution.
These observations were consistent with every group, as images on the Internet of a lab aren't too hard to find and compare to data stated in the lab.
Part1A) Our results showed that the dialysis bag formed a selectively permeable membrane that did not allow starch to diffuse out of the bag. We were able to see that the bag did allow glucose and potassium iodide to diffuse across its selectively permeable membrane through a glucose test and our observations. We took an initial glucose of the beaker full of water and potassium iodide, and the test affirmed that there was no glucose present in the beaker; however, after placing the dialysis bag full of glucose and starch in the beaker and allowing time for diffusion, glucose did indeed diffuse out of the dialysis bad. Our glucose test affirmed that there was glucose present in the beaker. Using our oberserations, we deducted that the potassium iodide did diffuse into the bag, for the colorless nature of the bag changed to blue. Osmosis of water cannot account for the change in the color of the bag, so potassium iodide must have diffused into the bag since the combination of starch and potassium iodide yields a blue color. Through this knowledge of knowing that a mixture of starch and potassium iodide will be indicated by a blue color, we were able to deduce that starch did not diffuse out of the bag because the color of the solution outside of the bag but I'm the beaker remained yellow, the initial color of the potassium iodide and water solution.
Part1B) After placing dialysis bags full of different concentrations of sucrose ranging from .2M - 1M and using a control group of distilled water, we were able to see changes in the mass of the dialysis bags. Since the beakers were full of solely water and the dialysis bags had differing concentrations of sucrose, we essentially were able to create a hypotonic solution. There was more sucrose in the bag than outside the bag. Our results showed that the higher the Molarity of sucrose in the dialysis bags the increase in mass after removed from the beaker of water was greater. Compared to the control group the other dialysis bags with differing concentrations of sucrose absorbed more and more water as the Molarity of sucrose increased. This demonstrates that the in order to balance out a higher molarity of sucrose in the bag more water diffused into the bag. There's a clear direct relationship between the molarity of the sucrose in each dialysis bag to the percent change in mass after it was removed.
Part1C) After soaking the potato cores in different sugar solutions, we noticed a change in the initial and final weight of the potato cores. This change is due to the molarity of the solutions the potato was soaked in. The higher the molarity, the lower the percent change of mass tended to be. The potato cores lost the most weight in the over night soak in the solutions with the higher molarity. This test of water potential is proven through this change in weight. As the potato cores sat in different sucrose concentrations, the potato increased water potential as the molarity rose. This shows an inverse relationship with molarity and the water in the potato.
Part1E) This part of the lab was conducted from various pictures online (shown in the graphs and data portion of our lab) and it was to prove that solutions of different concentrations around an onion cell cause the onion cell to undergo plasmolysis. This lab proved that the higher the concentrations of solute around the cell, the more water wants to leave the cell. Thus, the cell membrane contracts and shrinks as water diffuses across the membrane. The more water that diffuses out of the cell, the more the membrane shrinks and contracts.