Osmosis and Diffusion Lab (10/21/2013)

 

Purpose:

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. 

 

 

 

 

Introduction:

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. 

Class Data:

 

Graphs

Part1A)

Part1B)
All solutions inside bag with increasing molarity soaked in water

Part1C)

Part 1E)

Isotonic

Method:

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. 

Discussion:

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. 

Conclusion:

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. 

References:

Lab

http://iweb.tntech.edu/mcaprio/rbcs_and_osmosis.htm

http://www.waycross.edu/faculty/bmajdi/bio1labslides.htm

http://www.visualphotos.com/image/1x6586398/onion_cells_hypotonic_solution

 

 

 

 

 

 

 

 

Field Experience for Dhruv Patel

I enjoyed the field trip to Glacial Park for a variety of reasons. One of the most crucial reasons why I found my experience worthwhile was because of the hands-on experience I was able to receive. Since my family doesn't have a garden or doesn't grow vegetation at home, it was an unique experience to water trees, sow seeds, and plant acorns. This experience also gave us a glimpse as to the amount of hard work that farmers must and ecological sites must put in every single day. I can say on the behalf of nearly everyone who planted acorns that after a certain limit, we felt like putting in multiple acorns in one hole. This, however, defeats the purpose of the planting acorns, for the purpose of planting acorns is to actively distribute the planting of trees. This type of experience can't be taught in the classroom, and that's why I believe it was nice to have been able to step inside someone else's shoes for a day. Restoration ecology has only benefits, and I feel that helping an area recover faster from environmental degradation, regardless of the area's size, is worth it. 

Restoration Ecology assignment

Abel Lara, My Experience with Restoration Ecology
My experience in the field of Restoration Ecology was one of a kind. With my fellow classmates we watered plants, planted acorns, and removed shrub. All of these actions required time and the effort of the group as a whole. Together however we got a lot done. We were able to remove quite a bit of shrub, even though in comparison to all the shrub it is quite minimal. In any case it makes a difference. So, yes it is necessary and worthwhile to contribute to nature by removing invasive species, planting seeds that are native to the ecosystem ,and watering plants. If everyone could do whatever it is they can to contribute to the restoration of an ecosystem or maintain nature in general, each contribution would add up and make a difference. The benefits of Restoration Ecology are many but a few I can list are without a healthy ecosystem people would cease to exist, because we depend on primary producers such as plants who derive their energy not just from the sun but water and CO2 therefore it is crucial that we keep these native plants alive and the invasive species who just block the way: keep them out. I think that the most important thing i got out of this trip was that a lot of people are ignorant of the ecosystem. And I have learned to be more conscious of nature. I will certainly apply what I have learned to contribute to nature, because in the end it will benefit me and my fellow people.*
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Jakub Niedzwiecki Reflection on Glacial Park

I had a great time at glacial park. From planting tiny acorns in a savannah prairie, to going waist deep into buckthorn with a hand saw, I think this trip was a valuable, hands-on learning experience. 

                                                

This trip was beneficial because we actually got to experience what restoration ecology is all about. We learned about the importance of getting rid of invasive species from an area so life can exist naturally. We helped restore the indigenous life by removing the buckthorn and honeysuckle out of the area. We helped Mother Nature do what it does naturally.  We sped up the natural cycle by getting rid of the unwanted species of invasive plants and let the forest reclaim its natural land. I thought this was pretty amazing. 

Another aspect of restoration ecology that we got to experience was the managing and planting of the savannah prairie.  

We planted acorn seeds as well as watered some 50+ of oak saplings. This was a rewarding experience because one day, probably not in our lifetime, there will be an oak tree forest in the location where we planted those acorns. 

I think that restoration ecology is a vital area of study for modern society. Our work there on Wednesday was minute in the grand scope of things but it was significant in learning how humans can maintain nature as well as destroy it. A lot of hard work goes into fixing it, but very little is thought about it when we harm it. It was a humbling yet enriching experience. 

Acids and Bases Lab

Purpose- The purpose of this lab was to test for how different substances reacted with an acid (HCL) and a base (NaOH). We also tested for how resistant or susceptible each substance was to the acid and base. This determined if the substance was a buffer. In order to have a control group and a foundation for data comparison, we tested the effects of the base and acid on water. 

Introduction- In order to understand this lab, one must first be familiar with the properties of acids and bases. On the pH scale, the acids are at the lower ends of the scale (0-6), neutral substances in the middle (7), and basic substances in the upper end (8-14). The pH of a substance is determined to its relative hydrogen (H+) ion concentration and its relative hydroxide (OH-) concentration. Acids have a higher H+ concentration and bases have a higher OH- concentration. What this means is that acids are more likely to release or "donate" its H+ ions and bases are more likely to receive or "accept" H+ ions. 

 

             

     With the whole "donating and accepting" process in mind, the next step is to talk about substances that act as an equalizer of H+ ions. These substances are called buffers. Buffers absorb H+ ions and release it when needed, allowing it to balance and resist pH changes in that substance. 

Class Data

Material Tested Add

pH after adding this many drops

Material Tested Add

pH after adding this many drops

Graphs
Water's pH

















Orange juice pH

Buffered Aspirin pH

Chemical Added

Base=NaOH=red
Acid=HCl=blue

Method- During the lab, we followed an organized procedure. It is important to be as clear and organized as possible in the lab station, so we first labeled one of the 50mL beakers acid and the other base. The first substance we tested was the control group, water. We placed one of the probes that would record our data, the pH levels, into each beaker. Then, we added 5 drops of acid in one beaker and base in the other beaker. Stirring the HCl-water and NaOH-water solutions, we made sure that we would achieve the highest possible accuracy. After placing the probes in each solution, we were able to measure the changes in pH. We kept adding 5 more drops of acid and base until we reached 30 drops added in each solution. Cleaning the 50mL beakers and rinsing the probes, we made sure that we would not encounter any experimental error as we moved on from the control group to our next substance, orange juice. We followed the same procedure summarized above for orange juice and the buffered aspirin.

 

Discussion- The pH of the acidic beaker and the pH of the basic beaker are at the opposite ends of the pH spectrum. The pH of the base is above 7 and the pH of the acid is below 7. The control group is ran with water in order to have a starting point of pH levels as we gradually add 5 drops until we reach 30.

Our results line up rather nicely with the class data. One other group tested the orange juice, and our data combined data did not vary significantly. After the first five drops of acid, the pH of the orange juice dropped to about 4.45 for both groups. After gradually adding the acid, the pH kept decreasing in order to signify the increased acidity. After thirty drops, the orange juice registered at about 4.36 pH. This shows that the already acidic orange juice does not act as a good buffer, and it reacts positively with the acid. It takes on acidic properties as the acid is added.
               Our validity for the buffered aspirin test is a little skewed. Our group, in the middle of the test, switched the probes so the basic probe went in to the acidic substance and vice versa. So our data up until the 15th drop is unreliable. However, as we cleaned and situated our probes into their proper places, we can see that the aspirin's reaction with the base and acid is as follows. The added acid greatly decreased its pH while the base increased it greatly. This goes to show that the buffered aspirin in fact is not a good buffer. It does not show that it has the potential to level out the pH levels due to its positive reactions with the acid and the base.
              
               Our data for the water test is somewhat reliable. The base increased its pH content but, somehow, the acid did not decrease it. In comparison with other groups, this should not be the case. The acid should have decreased the water's pH levels while the base should have (and it did) increase the pH levels. While starting out at the neutral 7 on the pH scale, as the base was added, the pH rose multiple degrees, sometimes even passing 11. The acid decreased the water's pH multiple degrees as well, for other groups. Ours, not so much. This could have been due to the fact that the probe wasn't working properly, or that we may have been taking our data wrong.



Conclusion-  We set out to complete this lab so that we could find which substance provides the best buffer. Buffers will not change pH very easily. According to our set of data and the class set of data, the substance that appears to provide the best buffer out of the substances tested is Orange Juice. This is because the total buffer range for Orange Juice in our set of data was .23, and some other team that tested Orange Juice calculated a total buffer change of .27. It was to our benefit of having access to the class data table, for we are know able to clearly see whether our data is validated by other experiments. .23 and .27 are very close values, so this serves to prove that there is a low chance that a significant experimental error occurred during our examination of Orange Juice. 

References-  

http://www.youtube.com/watch?v=avnjBlicpFk 

Images: http://en.wikipedia.org/wiki/PH