Thursday, March 13, 2014

Gel Electrophoresis Lab

In this lab, we had 5 DNA samples and 3 restriction enzymes. We then had 5 different tubes that contained mixtures of DNA and restriction enzymes. We then placed these samples into the wells on the gel. The samples specifically contained: 
1. Marker (Only contained DNA)
2. DNA + PstI
3. DNA + PstI/HpaI
4. DNA + PstI/SspI
5. DNA + PstI/HpaI/SspI
After the samples were in the wells, we placed the gel into the gel electrophoresis machine. Once in the machine, an electric current is run through the gel to move the DNA down the gel. The lighter pieces moved to the end and the heavier pieces stay towards the wells. After the pieced had moved, we measured the distance the fragments had moved and compared them to the marker.
Gel electrophoresis works by the cuts in the DNA going through this gel. Each length stops at a certain point. The longer strands stay close to the top, or negative end, while the shorter strands go towards the bottom, the positive end. This is because the strands have to snake themselves between all these holes in the gel. The longer ones get caught and can't move as far down on the gel as the shorter ones can.  

Friday, February 14, 2014

DNA Replication Review Video

Here is the quick review of DNA Replication that our lab group put together:

Friday, December 20, 2013

Yeast Lab

Purpose: The purpose is to demonstrate the contrast between the reproduction of a culture if yeast if all one type and one of a mixture. We are going to observe how much reproduction occurs in a sample of all a type, all alpha type, and a sample of a group with mixed typing. 


Cells communicate by sending and receiving signals that come from other places such as the environment or even other cells. To trigger these responses the signals have to cross the membrane by either crossing itself or using receptor proteins that are in the surface. Yeast are unicellular fungi. Not much is needed for them to survive except for reduced carbon, nitrogen, biotin and salts and trace elements. Yeast is anaerobic and go through alcoholic fermentation. They also reproduce both asexually and sexually. When they reproduce sexually they need an alpha and an "a type" yeast cell. They then will grow towards each other once they receive each others fermone. They then will turn into a zygote and eventually reproduce. In our mixed culture of A and Alpha type you will observe:

                                                               Third Image is a single Zygote
Single and Budding Haploids:
                                                       Pink is Single and Blue is Budding
Methods: In this lab, a-type and alpha-type yeast cells were used. Using three test tubes, one containing a-type, 2 ml of water, and liquid agar, then two more were made using alpha-type yeast and a mixture of the two. Each culture was observed under a microscope at different time intervals, and the haploids and budding haploids were counted for the solutions containing one type. For he mixed type, haploids, zygotes, and asci were counted. The cells were counted at intervals of thirty minutes, twenty four hours and forty eight hours. The various types of cells were observed, counted, and documented in three different fields of view per culture. 


Graphs and Charts:


In our lab, we focused on two types of yeast. A type and alpha type. There were few differences seen between the two types, however, I noticed that the A type seemed to produce asexually a lot more than the alpha type did. Looking at our data this is also supported. Other than the sheer amount of the haploids we could see, very little else is different.
                                                         A Type Yeast at 48 Hours

                                                          Alpha Type Yeast at 48 Hours

 However, when we look at the mixed culture and our two separate cultures, we notice plenty of different things.

Mixed Culture at 48 hours

         Things formed in the mixed culture that we didn't see in the two isolated cultures. We observed not only single and budding haploid cells as we did in the isolated cultures, but we also saw shmoos, single and budding zygotes, and asci. These different things were the result of the mating occurring between the two types. As the time went on the yeast mated more and more producing more yeast molecules as can be seen in our data. They find each other by releasing pheromones that act as a signaling molecule in a G coupled protein receptor. This signal molecule allows the G coupled protein receptor to activate and produce the cellular response of growing towards each other and then mating. Since the two types of mating are very visually different it would be easy to conduct an experiment to determine which type was which if given a blank plate with no label. You could make two samples and add A type to one and Alpha type to another and which ever begins to form the different things such as shmoos, single zygotes etc. then you would know whether it was alpha or A. 


The yeasts in the mixture had a lot of single haploids instead of having more asci. Even after 48 hours there wasn't that many asci. There was no set ratio that went on in the mixture. But there seemed to alway be more single haploids than anything. There weren't that many shmoos and budding zygotes. What we conclude is that when we looked at the yeast they had already gone through those phases. There were more single zygotes though. There was a difference between the alpha and a type yeast cells. A type produced asexually more than alpha did. Though at each observation we observed vastly more cells, the relative concentrations of each type of cell remained relatively constant.  

Also the lab background 

Thursday, December 5, 2013

Plant Pigments and Photosynthesis

Lab 1

Purpose: The purpose of this lab was to be able to see the many different pigments that make up the leaves colors. This would provide us with an explanation of why the leaves change colors in the fall. 

Introduction: Chromatography is used to separate the pigments of the leave. The paper allows the different pigments to grab onto the paper and begin to spread at different speeds causing them to separate. This allows us to observe which pigment moved up the farthest and also to see all the pigments that go into the color of a leaf. 

Methods: For this experiment, we put 1 cm of solvent in the bottom of a graduated cylinder. We then took a piece of filter paper, cut it to a point, and used a coin to rub some of a spinach leaf onto the paper. We then submerged the tip of the filter paper in the solvent, allowing it to move up the paper and carry the pigment with it. When it was near the top, the filter paper was removed and the location of each band of pigment was marked.


Distance from the solvent line.

The paper used and next to a ruler

Discussion: The first time we did this expirement we didn't add enough pigment, so the lines were not visible. The second time we did and the pigments went up the paper. Chlorophyll B was the one that went up the lowest with 33 millimeters from the point. Xanthophyll was next with 43 millimeters from the point. Chlorophyll A was the third from the point which was 72 millimeters. The fourth was beta carotene with 129 millimeters. We could have added more pigment for better results and brighter more defined lines.

Conclusion: This lab demonstrated that there are many pigments involved in gathering energy from the sun. The different locations on of these pigments on the filter paper demonstrated the varying amount of these pigments, as well as the relative solubility of each. 


Lab 2:

Purpose: The purpose of this lab was to see the effects of DPIP, boiled or unboiled, and amount of light on the percent transmittance using a spectrophotometer. Our control group was cuvette one because it contained no DPIP, unboiled chloroplasts and was exposed to light. The other 4 were our experimental groups. 

Introduction: Spectrophotometers are used to measure the percent of transmittance from a solution placed in the machine. Transmittance is the amount of light that makes it through the solution. Absorption is how much of the light is absorbed by the solution.  Spectrophotometers use a light source that is shined through the solution and on the other side is a sensor that measures how much is transmitted through the solution and how much is absorbed.

Methods: We first added distiller water to a phosphate buffer, this was in all of the test tubes for all five solutions. Then we added DPIP and boiled or unboiled chloroplast to the test tubes. Then we filled the cuvettes three quarters of the way full and put it in the colorimeter. We put the cuvettes behind a light for five, ten and fifteen minutes. We took the readings of how much light was transmitted through.
The amount of each item we needed to put in each test tube.
The lest up we used for to have light in the cuvettes.


Graphs and Charts: 

Discussion: Only the graph of our 2nd attempt is pictured above. In our first attempt, we got very strange and inconsistent data, but using double the DPIP for our 2nd attempt corrected the problem.  Looking at our graph, it can easily be observed that cuvettes 3 had the highest transmission. This is almost certainly because it most closely mimicked natural photosynthetic conditions. The chloroplasts were unboiled and therefore not  denatured, and there was light shining on it. This allowed the electrons in photosystems I and II to be excited, beginning photosynthesis and eventually processing DPIP, turning the solution from blue to clear and allowing for a higher transmittance. On the other hand, all the other cuvettes showed a much lower transmittance rate, because in each case the chloroplasts were either boiled, starved of light, or both, preventing photosynthesis from starting and therefore causing DPIP to remain unprocessed and the solution to remain blue. 

Conclusion: The lab shows that transmition of light through the solution is best in conditions that are like the natural conditions of  a plant. DPIP is processed when there is light and unboiled choloroplast. Light and non denatured chloroplasts are essentual for photosynthesis to occur, so seeing that the solution that was most like natural photosynthetic conditions had the most light transmittance, meaning it was most effective at photosynthesis. 

Lab 4 Plant Pigments and Photosynthesis

Sunday, November 17, 2013

Cellular Respiration Lab

Purpose:   The purpose of our experiment was to see how germination and temperature effected cellular respiration. The independent variable for the experiment was the temperature and whether or not the seeds were germinated. The dependent variable was our seed which was corn. 

Introduction:     This experiment showed us that many factors can act on cellular respiration. Before we talk about the results of our experiment, we need to understand our experiment. One of our factors was germination. All germination means is when a seed begins to sprout and grow. This can be affected by the temperature, which we also tested. These things can affect cellular respiration because if the seed wasn't germinated, then it couldn't respire, because it's dormant. The cool temperature would affect it because the low temperature slows it down. 

Methods: We started with 25 dormant pieces of corn, 25 germinating and 25 glass beads as our control group. We placed them into a dry glass bottle and put a carbon dioxide detector on top. The detector measured the gas given off in each trial, and the data it picked up told us how much each group respirated.  

Graphs and Charts:



In this experiment there was higher rate of respiration when the germinated corn in cold water was higher than the rate of germinated corn in room temperature. The rate of the cold water corn, 17 degrees Celsius, was 1.0006 ppm/s. The rate of the corn at room temperature,which was 22 degrees Celsius, was .92043 ppm/s. The rate of respiration for the corn that was non-germinated was .20413 ppm/s. This was also done at room temperature.when the temperature was lower and the seed was germinated it had the lowest. This can happen because when the concentration of ATP drops then the respiration speeds up, and when the concentration of ATP is up the respiration drops. When the water is colder is slows down the energy speeding up the rate, which is why the cold water produced a larger rate. This also explains while the non-germinated seeds had a smaller rate, there was energy stored in the corn so the respiration was lower. With the control graph, the graph showed that there was respiration. There was glass beads in the container so there was no respiration, but because we didn't waft the CO2 enough it made the detector seem like there was CO2 in it.

Conclusion: Looking at our data would imply that the corn had a higher rate of respiration in cold water than at room temperature. The glass beads, though not perfect, stayed close to a rate of zero, but this fluctuation is almost certainly due to an error in experimentation. Non germinated corn respirated the slowest, then room temperature corn followed by corn germinating in cold water, which has the highest rate of respiration. 

Reece, Jane B. Campbell Biology. San Francisco: Pearson Benjamin Cummings, 2011. Print

"Plants In Motion." Plants In Motion. N.p., n.d. Web. 18 Nov. 2013.

Tuesday, November 5, 2013

Enzyme Catalysis Lab

Lab 2A:

Purpose:    The purpose of lab 2a was to see the effects of temperature on enzymatic activity and to see the presents of catalase in living tissue. We know that enzymes may act differently when it isn't performing at its optimal pH and that enzymatic activity can be amplified by the presents of a substrate. This experiment demonstrates these things. The independent variable in this experiment was the substances being added ( the temperature change or the potato/liver). The dependent variable is the product that comes from the reaction.

Introduction:      As I mentioned, enzymes activity can be affected by a few different things. These things are temperature, pH, and chemicals that influence the enzyme. Enzymes function at an optimal pH and temperature. Once the enzyme leaves that optimal value a few things could happen. In the case of temperature, once the enzyme goes past it's optimal temperature it denatures, meaning that it loses its shape due to disruption of bonds. Another way that the enzyme may be effected positively is by something we call cooperativity. When a substrate binds to the active site of an enzyme in its active form it increases the chances of other substrates being able to bind and produces more product. 

Methods:     At the start of the experiment we wanted to observe the basic reaction that we would be study. To do so, we put 10 mL of a 1.5 % solution of hydrogen peroxide into a beaker. We then added 1 mL of the catalase solution. After completing this and seeing the reaction, we then began the test of temperature.  First, we took 5 mL of the catalase and put it in a test tube. We then placed the test tube in a boiling water bath for 5 minutes. After the catalase had cooled, we out 10 mL of the 1.5% solution in a beaker. Then we added the cooled catalase and observed the reaction. Our last test was to demonstrate the presence of catalase in living tissue. What we did to show that was, we first cut a 1 cm3 piece of potato and once again set up our 10 mL of the 1.5% solution in a beaker. 
We then placed the potato in and observed the reaction one last time. 

Graphs and Charts:    Since the lab was not actually performed but us, leaving us with no data or charts to fill in, here is a graph from our book. This graph shows how the temperature affects the enzymes.

Discussion:      What we noticed in our first part of the experiment were that bubbles appeared. These bubbles were O2 (also our product). These bubbles are formed because of the H2O2 being broken down. This was just a normal reaction and it did what it was supposed to do. If the enzyme and the substrate are operating in its optimal conditions, then the reaction should occur and eventually slow to a halt. We then wanted to see the affects of temperature. What we noticed was that no bubbles were formed during this reaction. That's because the catalase was boiled therefore leaving its optimal temperature and because of that it denatured. What it means to denature is that it's "a process in which a protein loses its native shape due to the disruption of weak chemical bonds and interactions, thereby becoming biologically inactive". All that is saying is that when the heat is raised too high, the bonds are broken and the enzyme can't perform work anymore. We didn't see the bubbles because the catalase had been boiled to a point where it changed the active site and the substrate couldn't bond to the enzyme and then couldn't produce the O2. Then in our final test, we wanted to see if catalase was present in living tissue. When we placed the potato in, the reaction once again occurred. We saw this because there was in fact catalase in the potato. A question posed by the lab was, "what if the potato had been boiled before we placed it in the beaker?". The answer to that is, that we wouldn't see a reaction. The heat would have also denatured the catalase in the potato producing no reaction. 

Conclusion:    As this lab demonstrates, enzymes are very specific molecules that can't always work in whatever they are thrown into. What makes this all relevant to us is that we have enzymes inside us! What happens to us when we have a fever? And our enzymes begin to go past their optimal temperature? This is why people can die of high fevers. Humans enzymes can't function that high either and denature and we die. This is why it's so important that we learn about this things, because they can apply to you and me in our every day life. 

References:  Reece, Jane B. Campbell Biology. San Francisco: Pearson Benjamin Cummings, 2011. Print

Lab 2. Enzyme Catalysis. College Board.

Lab 2B:

The purpose of this experiment was to find an initial base line. There was no independent or dependent variable because this was the control itself this was the dependent variable.

Enzymes are macromolecules that act as a catalyst. They speed up the metabolic reactions by lowering the energy barriers. They speed up the reaction without consuming the reaction itself.

We added 1.5% hydrogen peroxide, water and sulfuric acid. When this was combined we titrated it so we could then get a baseline to use for the next experiment.


With finding the base line we figured out how much hydrogen peroxide is used in the experiment we conducted after. Our baseline ended up being 3.7. 

This experiment helped the future ones we did because without it we would not have a control for the other parts of lab two.  

Robert B. "Chapter 8." Campbell Biology Ninth Edition. N.p.: n.p., n.d. N. pag. Print.

Lab 2C:

Purpose: the purpose was to determine the rate of spontaneous conversion of hydrogen peroxide to water and oxygen.

Introduction: An enzyme is a chemical that catalyzes, or speeds up, a reaction and is not consumed in the process. A substrate binds to its active site, and the enzyme speeds up an otherwise slow reaction and releases the product. In the case of the enzyme in this experiment, catalase, it speeds up the breakdown of hydrogen peroxide into water and oxygen. This is essential in the human body, because a buildup of hydrogen peroxide is toxic to humans, but catalase converts it into substances usable by the human body. 

Method: In this lab we took 10 mL of hydrogen peroxide that sat overnight, 1mL of water and 10 mL of sulfuric acid. After it was mixed we took 5 mL of the solution and titrated it. The amount of KMnO4 used was 4mL.


Discussion:    In this lab, we added Potassium permanganate to our 1.5% solution to see the rate of spontaneous conversion from H2O2 to H2O and O2 with an uncatalyzed reaction. What the potassium permanganate does is it shows how much hydrogen peroxide is left in the solution after it had been allowed to sit. A problem we have with our data is that we found a negative number for our amount of hydrogen peroxide that was spontaneously decomposed. That doesn't make sense, because once the reaction has occurred, it can't return to its original form since the oxygen has already escaped into the air. This impossible number is most likely due to an area we had in calculations. We also found that the percent of the hydrogen peroxide that was spontaneously decomposed in 24 hours was only 25%. That number also should have a been higher. This is probably once again due to an error in the set up of the lab or the calculations. 

Conclusion: the rate of conversion of hydrogen peroxide to water and oxygen is about 25% per day uncatalyzed  this data will be helpful to compare to in later reactiins wiht catalase added.

Citations: Campbell Biology Ninth Edition, College Board Enzyme Catalysis Lab.

Lab 2D:

Purpose: the purpose of this experiment is to determine how much hydrogen peroxide can by catalyzed by the enzyme catalase within various windows of time. The independent variable of this experiment was the amount of time the catalase was allowed to react, and the dependent variable was the amount of hydrogen peroxide consumed. 

Introduction: An enzyme is a chemical that catalyzes, or speeds up, a reaction and is not consumed in the process. A substrate binds to its active site, and the enzyme speeds up an otherwise slow reaction and releases the product. In the case of the enzyme in this experiment, catalase, it speeds up the breakdown of hydrogen peroxide into water and oxygen. This is essential in the human body, because a buildup of hydrogen peroxide is toxic to humans, but catalase converts it into substances usable by the human body. 

Methods: First we put 10 mL of 1.5% hydrogen peroxide into a cup. We added one mL of catalase extract and let the substance react for 10 seconds, and repeated the process for increasing amounts of time before stopping the reaction by denaturing the enzyme with sulfuric acid. We titrated potassium permanganate into the solution to determine how much hydrogen peroxide was reacted.


Graphs and Charts:

Discussion: The most obvious trend in our data is that as the enzyme was allowed to react for more time, we had to titrate less and less potassium permanganate, meaning increasing amounts of hydrogen peroxide were consumed. This is because the more time catalase was allowed to react, the more hydrogen peroxide it was able to break down, because the enzymes had more time to move on to more substrate after breaking one down. This data did fluctuate, most notably at the 60 and 120 second trials, but this is almost certainly an experimental error. We were probably impatient in our titration, and added more than necessary, giving us an inaccurate reading. But, the overall trend was that more hydrogen peroxide was consumed when the catalase was given more time to work, which would make sense, because giving catalase more time gave it more time to break down hydrogen peroxide. 

Conclusion: The more time catalase is given to work on hydrogen peroxide, the more will be broken down. This trend is supported by our data with a couple errors, but comparing our data to that of other groups showed that these data fluctuations were just errors. Overall, we can conclude enzymes can break down more substrate given more time to react. 

References: Campbell Biology Ninth Edition
Lab 2: Enzyme Catalysis, College Board

Monday, October 21, 2013

Diffusion and Osmosis Lab

The purpose of this experiment was to see how diffusion worked within starches, glucose, and iodine. It also is to look at an example of selectively permeable walls.
A selectively permeable membrane is set up so molecules or ions can not be too big. Only molecules of a certain side are allowed to go through the membrane wall. The molecules that are supposed to go through even need help from protein carriers.
We soaked a piece of dialysis tubing in water and tied one end to make it a bag. We then filled it with a substance that was 15% glucose and 1% starch. We placed the bag into a a solution that was part iodine and part water. After a few minutes the solution inside the bag turned blue.

In the lab, the difference between the initial presence of glucose was 15%. As the iodine diffused into the dialysis tubing, the glucose and starch turned blue. This is an example of a selectively permeable membrane. The iodine goes inside the dialysis tube and the glucose comes out. The cup of iodine and the dialysis tube went through diffusion as well. When the two sections hit equilibrium the glucose presence was 5% in both.
This lab shows that diffusion and a selectively permeable membrane go hand in hand. Diffusion can happen with any type of membrane really but works best with a selectively permeable membrane. Our lab worked but didn't work as well as it could have. We put too much water in our iodine and water solution so it took almost twice as long for our tube to become fully blue.
Reece, Jane B., and Neil A. Campbell. "Membrane Structure and Function." Campbell Biology. Harlow: Pearson Education, 2011. N. pag. Print.
Purpose: The purpose of this experiment was to see what would happen when a membrane that was selectively permeable was placed in either a hypotonic, hypertonic, or isotonic. This was being tested in relation to the concentration of the substances. We wanted to see which would move through the membrane by a process called osmosis. The independent variable would be the molarities of sucrose and the dependent variable would be the mass of the bags.

Introduction: In this experiment, we were dealing with the process of osmosis. Osmosis is the diffusion of water across a selectively permeable membrane. If we think about the example of the U-shaped glass tube with a selectively permeable membrane in the center, the water will want to move to the side with the higher solute concentration. If you think of the solute and solvent as a ratio, the solvent moves to even out the ratio on the side with a lower solute concentration.

Methods: First, we needed to obtain six strips of dialysis tubing. We tied off the tubing to make a bag and filled them with 5 different molarities of sucrose and one filled with distiller water (our control group).  You then closed the bag leaving enough room for osmosis to occur. After the bags were filled, we took the mass of each. We then took the bags back to our table, put them in cups labeled with which solution it was. We filled the cups with water and let them sit for about 30 minutes.  After 30 minutes had passed, we removed the bags from the cups, and weighed them once again.

Data :

Graphs and charts:

Discussion: By looking at the data of this lab alone, I am not sure I would understand the relationship between Molarity and mass. The  trend we  should be seeing is as  the Molarity gets larger, so should the percent change of the mass.  As the Molarity increases, it takes more water to try and balance out the solution inside and out a state that we call equilibrium. The water naturally wants to balance out the concentration across the membrane. I don't think that our data necessarily showed that. Just by observing the lines that the plotted data makes (both class average and lab group) it zig-zags. In a perfect world, the lines would just gradually slant upwards. This discrepancy in data could be due to the dialysis bags not being filled with the same amount of liquid. It could possibly be due to amount of liquid in the cup, or an error in the weighing process. The results of the lab were what I expected them to be because I knew that since Bag F had the highest concentration of sucrose, it would take the most water to balance. Our data wasn't what I expected because I thought that like I said the lines would just go up not up and down.

Conclusion: Overall, I think that our data was helpful to see a trend I was already aware of. Had I not known what I was looking for our data would not have lead me in the right direction. Our lab data shows however, that the membrane was selectively permeable and that therefore the mass will increase.

References: Reece, Jane B. Campbell Biology. San Francisco: Pearson Benjamin Cummings, 2011. Print.

Lab One Diffusion and Osmosis. College Board  

Purpose: The purpose of this experiment is to analyze the water potential of potato cells, and it's correlation to the molarity of sucrose solutions. The independent variable was the various molarities of the sucrose solutions and the dependent variable was the final mass of the potato cylinders. They were soaked in water as well as a control. 

Introduction: Molecules in cells are constantly moving and bumping into each other. They have a tendency to move from areas of higher concentration to areas of lower concentration in a process called diffusion. Osmosis is the diffusion of water molecules through a selectively permeable membrane (one that only allows certain substances  to diffuse across it.) Waters tendency to leave one area for another is measured by water potential (which is 0 in pure water.) 2 factors most influence water potential. The first is solute potential, which is the effect that the solute potential has on the solution's water potential. Water movement is also directly proportional to the pressure potential of a system, which limits the expansion of cells by exerting pressure back into the cell if it fills too much. Diffusion and osmosis are crucial in maintaining balance in the concentrations of various substances inside and out of the cell membrane.

Methods: We cut cores out of a potato and soaked them in sucrose solutions of various concentrations. We weighed them before and after soaking, and then calculated the mass difference and it's relationship to the sucrose concentration. 


Graphs and Charts:

Discussion: The most noticeable trend in our data is that the potatoes gained mass when soaked in water and 0.2M sucrose, but began to lose mass once the cores were placed in a sucrose solution of 0.4M and up. This most likely is because potatoes contain sucrose, and its concentration in potatoes is between 0.2 and 0.4M. When soaked in solutions of 0.0 and 0.2M, sucrose rushed out of the potato and into the water, while water rushed into the cores. This is why the potato cores gained mass when soaked in solutions of lower concentrations. However, when the potatoes were soaked in solutions with a higher concentration, water rushed out and they lost mass. The trend of continually lowering mass continued until our final test, 1.0 M sucrose. This could very well be an error in our experimentation, but since the other groups in the class had similar result I think it was the pressure potential of the potato cores limiting their water intake. 

Conclusion: The potato cores gained mass in solutions of 0.2M and less and lost mass in solutions of 0.4M and more. This leads to the conclusion that the sucrose concentration of potatoes is around 0.3M. It stopped losing mass at 1.0M sucrose however, possibly due to error in experimentation or possibly the potato exerting pressure on tats interior to stay the same size. 

Campbell Biology Ninth Edution
The purpose of this lab was to see how water and salt can affect the onion. It also shows how plasmolysis shrinks the cytoplasm. The independent variable is the salt concentration and the dependent variable is the tonicity of the onion.

Introduction: Cells have a tendency to move and bump into each other constantly. Diffusion is the result of this contact. Diffusion is the random movement of molecules to an area of lower concentration from an area of higher concentration. Osmosis is a variation of diffusion. This is the diffusion of water molecules through a selectively permeable membrane from a region of higher concentration to a region of lower concentration. Water potential is the measure of free energy of water in a solution. Dialysis is the movement of a solute through a selectively permeable membrane. When plant cells are placed in a hypertonic solution they lose water in a process called plasmolysis. Conversely, when placed In a hypotonic solution hey take in water and become turgid, and in an isotonic solution water flows in and out at an even rate and the cell becomes flaccid. This experiment takes place to measure the osmosis of water in and out of an onion cell.
Methods: First, you are to obtain the epidermis of an onion. After doing so prepare a wet mount and observe the onion under 100x magnification. Record what you see, and then add a couple drops of 15% salt solution. Draw the solution across the onion using a paper towel. Observe and then record the difference. Once that is done, flood the onion epidermis with water and describe what happens.
Graphs/Charts/Data:  First photo is the onion cell when it is turgid and the second photo is the onion cells flaccid or plasmolyzed.  

Discussion: Part E of the lab centers around plasmolysis. Plasmolysis is, "a phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall; occurs when the cell loses water to a hypertonic environment". In the case of onions, the plasma membrane is pulling away from the cell because of the 15% salt solution. In a normal hypertonic solution, onion cells would still have its plasma membrane pull away, but the salt helps draw the water out of the cell, which we can see by the change of color in the pictures. When the onion is flooded with fresh water again, it returns to its normal color and shape. We are placing the cell back into a hypotonic solution and the cell is turgid again.
Conclusion: Looking at the data, the onion seems to become more plasmolyzed. The more salt outside the cell, the more water has to rush out of the onion to balance the concentrations. The onion cells become turgid as salt is decreased and plasmolyzed as salt is added.
References: Campbell Biology Ninth Edition
Lab One: Diffusion and Osmosis College Board