Diffusion-Osmosis Lab

Purpose

1A: The purpose of this experiment was to determine the permeability of the dialysis tubing by identifying which molecules would or would not diffuse through it.

1B: The purpose of this experiment was to measure the effects of solute concentration on the osmosis of water through a selectively permeable membrane like a dialysis tube.

1C: The purpose of this experiment was to determine the water potential of potato cells and by measuring the diffusion of water into and out of pieces of potato in solutions of various molar concentrations of sugar.

1E: The purposes of this experiment was to observe the effects of immersion in solutions of varying tonicity on onion epidermis cells.

Introduction

1A: Diffusion is a kind of passive transport in which molecules move from an areas of high concentration to low concentration. Dialysis is the diffusion of molecules through a selectively permeable membrane, one that allows some substances but not all to pass through. Dialysis tubing is selectively permeable, allowing only substances small enough to fit through its pores to diffuse. Glucose,water, iodine, and potassium iodide are all relatively small molecules, while starch is a macromolecule consisting of many monosaccharides like glucose linked together.

1B: Osmosis is the diffusion of water molecules through a selectively permeable membrane. Isotonic solutions are at dynamic equilibrium, with molecules moving at equal rates in both directions through a membrane for a net change of zero on both sides. Hypertonic solutions have a greater concentration of solute than the opposite side of the membrane, so water rushes into them, while water leaves hypotonic solutions because of their comparatively low solute concentrations; thus, in standard conditions, water will always move from a hypotonic solution to a hypertonic solution until they reach equilibrium and become isotonic.

1C: Water potential  is a measure of the tendency of water to move to or from a place. It is calculated through a combination of the pressure and the solute concentration of the area. Water potential is directly related to pressure potential, but inversely related to solute potential. Addition of solute always decreases water potential so solute potential is always negative. The water potential of pure water at standard atmospheric pressure is zero. Areas of high water potential have high free energy and many water molecules, and water always moves out of areas of high water potential to ones of lower water potential.

1E: Onions are plants and have a rigid cell wall surrounding their cell membranes. When in hypertonic solutions, plant cells experience plasmolysis, in which water diffuses out of the cell and the cytoplasm shrinks. Because the cell wall does not change shape, the cell membrane pulls inwards and becomes detached from the cell wall. In hypotonic solutions, water flows into the cell and is stored in its central vacuole.

Method

1A: For this experiment, we used an approximately 15cm long dialysis tubing; a clear plastic cup; a 15% glucose and 1% starch solution; glucose testing strips; and an iodine potassium-iodide solution. After soaking and opening the dialysis tubing, we tied one end and poured the 15%glucose/1%starch solution into it. The iodine potassium-iodide solution was poured into the clear plastic cup. Both solutions were tested for glucose, and then (after tying up the other end of the dialysis tubing) we submerged the dialysis tubing into the iodine potassium-iodide solution. After 30 mins, each solution was once again tested for the presence of glucose.

1B:This experiment required 6 clear plastic cups; 6 pieces of approx. 15cm long dialysis tubing; distilled water; 0.2, 0.4, 0.6, 0.8, and 1 M sucrose; and a weight. After soaking and opening the pieces of dialysis tubing, one end of each was tied up and each of the previously listed solutions was poured separately into each dialysis tubing. The other ends were then tied up and each “baggie” was weighed and recorded. Meanwhile, each plastic cup was filled with distilled water, and once all the baggies were weighed, they were each placed into a plastic cup for 30mins. Once the time passed, each baggie was taken out of the cups, blotted dry and weighed again.

1C: The materials used in this experiment were as followed: a potato; a cork borer; six clear plastic cups; distilled water; 0.2, 0.4, 0.6, 0.8, and 1 M sucrose; plastic cling wrap; and a weight. Using the cork borer, 24 potato cylinders were cut out (and any pieces of skin removed!) and separated into groups of 4.Each group was weighed and recorded, while the solutions listed above were poured into each plastic cup separately. Once that was taken cared of, each group was placed into a solution filled cup, which were then wrapped closed with the cling wrap and left overnight. The next day, the groups of potato cylinders were taken out, blotted dry, and then each group was weighed and recorded.

1E: This experiment required: an onion; 15% NaCl solution; microscope; distilled water. First, we had to prepare a wet mount of a small piece of the epidermis of the onion which was then observed under 100X magnification. Once that was recorded, we added two drops of the 15% NaCl solution onto the specimen and recorded what we saw. After that we removed the cover slip, put water on the onion, and recorded the result.

Data

1A

 

1B

 

1C

1E

 

 

Graphs and Charts

Discussion

 1A: There was 15% gluecose and 1% starch in the bag. The bag was colorless inside, but then when we put it into the iodine potassium iodine solution and it turned blue.  We know that the iodine went into the bag because iodine reacts with starch and the membrane is permeable to iodine. The bag is not permeable to starch because it did not leave the bag. Before we put the bag into the iodine, there was no gluecose outside, but after being in the iodine potassium iodine, gluecose was found outside the bag. We used the strips that test urine to find if gluecose was present or not. We found that it was, this makes sense because starch is the largest solute, then gluecose, then iodine, and the smallest solute is water. Starch was not able to go across the selectively permeable membrane because it is large, but gluecose, iodine, and water were able to go through. We thought that the membrane was selectively permeable, and we knew that water would perform osmosis through the membrane, we knew larger solutes would be less likely to go through and perform dialysis.

1B: During this experiment we ran into a few technological malfunctions. We had just finished taking the bags out of the distilled water, weighed, and read the masses of the dialysis bags so we disposed of them properly, but our data and mass numbers got deleted FOREVER! We figured out our data eventually. While trying to find the percent change in mass, final mass minus initial mass must be divided by direct initial mass, then multiplied by one hundred.

As we measured the solute concentration of the osmosis of water through a selectively permeable membrane we found that the larger the amount of solute, the larger the percent change. As an example, for(A) Distilled Water, dynamic equilibrium should occur, meaning water goes in and out at the same rate, making this isotonic. The size of the bag should stay the same and ours was 16.3g before and after.  For (B) .2 Molarity of Sucrose, the mass should increase because the water is hypotonic, meaning it has less solute than the inside of the bag. Before we put it in the water it weighed 13.3g and when we weighed it after it weighed 13.8g, consisting of a percent change of 4%. Just as (B) (C-F) were also hypotonic, the percent change ranged from 9%-15%, but the bag of (F) 1 Molarity should expand the most because there is the most sugar inside the bag. The graph shows a direct relationship, as the Molarity of Sucrose increased, the percent change increased. Since life is always trying to reach an equilibrium, the water had to keep going in and spread out.

1C: While measuring the water potential of a potato core during this experiment our data shows that our results had an inconsistency. For Distilled Water and .2 Molarity of Sucrose, our data is acceptable becausethe potato cores in Distilled Water started at 12.6g and increased in mass by 1.6g, making it 14.2g.  The percent change for the potato core in this solution was 13%. The polato cores in solution with .2 Molarity of Sucrose was first 10.2g then increased in mass by .4g, making it 10.6g. There was a percent change of 4% in .2 Molarity of Sucrose. These two were good data because the solutions were hypotonic to the potato, so the water rushed in and made it become heavier. For solutes .4-1 Molarity of Sucrose, the potato core was placed in hypertonic solution where the water potential outside the solution was less than the inside of the potatoes. The water went from high concentration (potato) to low (solution), which caused a change in mass of the potato. At the higher molar concentration water moved out of the potato and moved in at lower molar concentrations. The graph shows an inversely related line because as the Molarity increased, the percent change decreased.

1E: Plasmolysis is the shrinking of the cytoplasm of a plant cell in response to diffusion of water out or the cell and into a hypertonic solution surrounding the cell. The onion showed the difference between how animal and plant cells would react. When the onion was in a hypertonic solution of 15% NaCl, more water went inside the vacuole than the amount that left the cell. The cell wall should begin to expand and became lysed. When in an isotonic solution the amount coming in and out were at equal rates. While in an hypotonic solution since the concentration of solute is less outside the cell wall the water rushes out.

Conclusion

1A: The membrane was selectively permeable and the smaller solutes such as gluecose, iodine, and water were able to diffuse and cross over. Using IKI to show test for starch, the color change showed starch was too big to fit through the membrane because it was still where it was in the beginning.

1B: This experiment proved that water moves across the selectively permeable membrane of the dialysis bag. The sucrose does not move easily through. We can conclude that sucrose must be too large to pass through.

1C: Since water potential equals pressure potential and solute potential, this experiment helped us conclude potatoes had lower water potential because they took in water while in the Distilled Water cup.

1E: From this experiment we were able to understand polymolysis and how the plant cells react in a hypertonic solution. Since the pressure decreased, it became weak when the water left the cell.

 

 

Into the Brush [Karolina]

A little disclaimer before I begin, I by no means do I mean to infringe on any copyrights by using that title (yes, I became super paranoid in the middle of the night and needed to add this). Anywho...

Last week, yours truly went on a daring adventure into the wild depths of McHenry's world renowned Glacial Park to aid in the battle against the evils of Honey Suckle and another just as dangerous invasive species that I'm sure you all have heard about- Buckthorn. At just past nine, I, along with all the other brave souls of Ap Bio, stepped out of the safeties of our yellow tanks and marched up enumerous mountainous hills to where we were told the battle would be held. Upon arrival we were divided into two groups, one would go and tend to lands already won where they would be instructed on regenerating the land through planting seeds, the other being sent straight to battle- I being put in the latter. There was no time for tearful goodbyes or last minute get-a-ways. With the tools that were handed to us, we set off!

Feeling rather self fulfilled with the task at hand, I chose to spend the three hours we were given to accomplish the mission right at the war front. What started as an impassible force of strong species quickly got brought to their knees by our trustworthy loppers and saws. Definitely the hardest task was bringing down a not two, not three, but four (!) Honey Suckles growing from one stump. Thankfully I had my ever so helpful co-soldier Amy Zahn at my side to bring that one down.

But why should this matter to you, a reader who is most likely lolling around comfortably on a couch or perhaps leaning back in your office chair? Because these species are taking over our forest preserves- the last connection that us suburban folk have left to nature close by. By doing so, they are killing off native plants, and driving those poor prairie animals away from their homes, because believe it or not these territories use to all be prairie/grassland. It's time we stood up for the little man! Down with Honey Suckle! Down with Buckthorn!



On a more serious note though, I do fully believe in restoration ecology because it is our fault that these species have made their way to these areas in the first place. By allowing them to continue growing and driving out native species, we are only furthering the problem because it is severely upsetting the ever so sensitive balance of the ecosystmem and will eventually completely destroy it by driving out all natural competition. Although we like to think of our selves as omnipotent, we are not. We too our dependent on the ecosystem we live in, so even if you are not a big "nature fan", at least think of yourself and all the other people you interact with.