Honori Yamada Bio 2 Sept/2/10 Introduction: The cell membrane is a thin barrier of a cell which consists of proteins and a phospholipid bilayer. However, only particular materials are able to diffuse in and out of the cell membrane and this is due to its size, charge, and polarity. Diffusion is a movement of any substance or particle in which they move in areas from high concentration to low concentration until equilibrium is reached. Out of several ways of diffusion that are possible, simple diffusion only allows nonpolar substances such as oxygen and carbon dioxide (O2, CO2) to get across the cell membrane. There are other ways such as the active transport which allows only ion charged particles as well as the protein transports, which allows specific polar molecules such as water (H2O) to enter in and out of the cell membrane. Yet, most importantly, there is also a special case of diffusion of water known as osmosis. As it is shown on the figure 1 below, this diffusion uses the semi permeable membrane to let water molecules go through from area of high water potential to an area of lower water potential. The movement of water molecules moving out of the cell is known as plasmolysis. Oppositely, the movement of water molecules moving into the cell until it bursts is known as cytolysis. In this research, the experiment will be investigated on whether the cause of different temperature will affect the diffusion between two substances. Two solutions, 25% salt water and normal tap water, will be used throughout the experiment. In the dialysis tubing, normal tap water will be inserted and will be enclosed. On the other hand, salt water will be contained inside a beaker and will be heated to a certain temperature degree. Osmosis will occur when the dialysisFigure 1: The basic movement of osmosis by its semi- tubing is dropped into the beakerpermeable membrane. filled with salt water. As the beaker contained solution is hypertonic, the water escaping out the dialysis tubing, or shrinking, can be predicted. Also, according to the collision theory of particles, it can be scientifically predicted that as temperature increases, the osmotic diffusion will occur easier and faster. Collision theory can be explained of how when temperature increases, the velocity or the energy of the particles in a solution will increase as well; which therefore increases the collision probability among the particles. Thus from this collision theory proposed by Max Trautz and William Lewis, it can be expected that plasmolysis will occur faster and easier accordingly as the temperature increases. (http://www.eoht.info/page/Collision+theory) From an internet source, a formula known as the Osmotic Pressure theory given by Van t’Hoff which describes the affect of osmosis according to different temperatures can be written as:
Honori Yamada Bio 2 Sept/2/10 π = c R T, (1) where π indicates the osmotic pressure, c is the molecular concentration, R is thegas constant, and T is the temperature. Van t’Hoff’s theory proves how the osmosispressure does not depend on the type of solute or the size of the molecules, but more ofthe 2 factors of concentration and temperature. As the temperature increases, so will theosmotic pressure. Similarly, as the concentration increases, so will the osmotic pressure.(http://urila.tripod.com/) From equation 1, it can be predicted that as the temperatureincreases, there will obviously be an effect on the osmotic pressure or in thisexperimental case, the diffusion across the semi permeable membrane.Design:Research Question:How will temperature affect the rate of diffusion between water and 25% salt water?Table 1: Important VariablesVariable Type HowTemperature Independent Variable Water bath, thermometer, hot plateMass of dialysis tubing Dependent Variable Beaker, waterSize of dialysis tubing Controlled Variable Ruler measurement, scissorConcentration of salt water Controlled Variable Electronic Balance, beaker, - Amount of salt water, stirrer - Amount of waterLength of time Controlled Variable StopwatchSize of Beaker Controlled Variable -------------▲Table 1: These are the important independent, dependent, and controlled variablesthat are shown as well as the process of how it was done.Materials: - Dialysis Tube - Hot Plate - Beaker Figure 3: Dialysis tubing and 2 clamps - Thermometer used through the experiment - Dialysis tubing clamps - Water - Salt - Electronic Balance - Timer Figure 2: Electronic Balance used - Graduated cylinder to measure all the dialysis tubings - Ice - Large bowl
Honori Yamada Bio 2 Sept/2/10 Procedure: Step 1. Prepare 320 ml of 25% salt water solution in a beaker (300 water, 75g of salt) Step 2. Cut the Dialysis tubing into 13cm lengths and rub it in water for friction to get an opening Step 3. Close one side of the Dialysis tubing with a dialysis tubing clamps Step 4. Insert 30 ml of plain water into the Dialysis tubing and secure the other side with a green clip Step 5. Prepare the hot plate or an ice bowl to the given temperatures (0˚C, 15˚C, 30˚C, 60˚C) Step 6. Place the beaker filled with 25% salt water onto the heating plate / ice bowl Step 7. Once the beaker reaches the certain temperature, keep it in a constant temperature and insert the Dialysis tubing Step 8. Time the experiment for 10 minutes Step 9. Remove the Dialysis Tubing and measure its mass on the measuring scale (repeat this 5 times for each 3 trials) Step 10. Later, repeat the whole process 3 times with the different given temperatures Step 11. After the experiment, calculate the averages of each 3 masses and its uncertainties Data Collection & Processing:Table 2: Percent Change in Mass at Different Temperature1°C Initial Result Average of Change in Mass Percent Average Weight(g) Mass (g) Masses (g) (g) Change D= Percent (A) (B) C= B – A Change 100Trial 1 40.68 1) 39.50 39.60 -1. 08 - 2.65 2) 39.66 3) 39.60 4) 39.65 5) 39.57Trial 2 42.49 1) 41.86 41.47 -1.02 -2.40 2) 41.68 -2.46 ± 0.16 3) 41.43 4) 41.26 5) 41.20Trial 3 42.12 1) 41.26 41.14 -0.98 -2.33 2) 41.15 3) 41.10 4) 41.12 5) 41.07
Honori Yamada Bio 2 Sept/2/1015°C Initial Result Average of Change in Mass Percent Average Weight(g) Mass (g) Masses (g) (g) Change D= Percent (A) (B) C= B – A Change 100Trial 1 41.75 1) 40.16 39.98 -1.77 -4.24 2) 39.83 3) 40.23 4) 39.78 5) 39.90Trial 2 41.04 1) 39.48 39.37 -1.67 -4.07 2) 39.32 -4.21 ± 0.13 3) 39.02 4) 39.67 5) 39.35Trial 3 40.55 1) 38.95 38.80 -1.75 -4.32 2) 38.96 3) 38.72 4) 38.71 5) 38.6430°C Initial Result Average of Change in Mass Percent Average Weight(g) Mass (g) Masses (g) (g) Change D= Percent (A) (B) C= B – A Change 100Trial 1 41.95 1) 40.53 39.98 -1.97 -4.70 2) 40.30 3) 40.19 4) 40.03 5) 40.09Trial 2 42.22 1) 40.22 39.77 -2.45 -5.80 2) 39.91 -5.56 ± 0.75 3) 39.73 4) 39.65 5) 39.35Trial 3 43.62 1) 40.93 40.92 -2.70 -6.19 2) 41.09 3) 40.83 4) 40.95 5) 40.8260°C Initial Result Average of Change in Mass Percent Average Weight(g) Mass (g) Masses (g) (g) Change (%) Percent (A) (B) C= B – A D= 100 Change (%)Trial 1 40.05 1) 37.98 37.63 -2.42 -6.04 2) 37.95 3) 36.95 4) 37.73 5) 37.55Trial 2 39.17 1) 36.88 34.78 -4.40 -11.23 2) 34.84 -9.05 ± 2.17 3) 34.74 4) 34.65 5) 34.45Trial 3 40.60 1) 36.93 36.59 -4.01 -9.89 2) 36.83 3) 36.55 4) 36.37 5) 36.25 ▲Table 2: Five dialysis tubings were weighed for each three trials and the average percent change in each mass were calculated with uncertainties.
Honori Yamada Bio 2 Sept/2/10Sample Calculations:i. Finding the Mean of all 5 result masses (trial 1 at temperature 1°C) = (result mass 1+result mass 2+result mass 3+result mass 4+result mass5)/5 = (39.50 + 39.66 + 39.60 + 39.65 + 39.57) / 5 39.60 (g)ii. Finding the Change in Mass (trial 1 at temperature 1°C) = Average of Result Mass – Initial Weight = 39.60 – 40.68 -1. 08 (g)iii. Finding the Percentage Change (trial 1 at temperature 1°C) = Change in Mass / Initial Weight × 100 = -1.08 / 40.68 × 100 - 2.65 %iv. Finding the Average Percent Change at 1°C = Trial 1 Percent Change + Trial 2 Percent Change + Trial 3 Percent Change / 3 = (- 2.65) + (-2.40) + (-2.33) / 3 -2.46v. Calculating the Uncertainty at temperature 1°C = Range / 2 = [(-2.65) + (-2.33)] / 2 ± 0.16Figure 4: The graph above shows how the percent change in mass is affected by thedifferent temperatures.
Honori Yamada Bio 2 Sept/2/10Conclusion & Evaluation:Conclusion: According to the graph in figure 4, the linear fit equation or the slope shows adescending line. The slope which was -0.11 signifies how when the temperatureincreases, the percent change in the mass of the dialysis tubing gets smaller. As thepercent change in the mass gets smaller at a high rate of temperature, this thereforespecifies a faster process of shrinking or hypertonic solution. The percent change inmass after placing the dialysis tubing in 1°C shrunk by -2.46%. However, the percentchange in mass after placing the tubing in 60°C shrunk by -9.05%. Again, this can beconcluded as to how the percent change in mass of the dialysis tubing decreases as thetemperature rises. From figure 4, the correlation of the graph was shown as -0.9989 which is adecent result and makes sense since the number is very close to -0.1. As the correlationwas very to -0.1, this means that there is a visible actual pattern or an effect of theindependent variable used throughout this experiment. The uncertainty of the graph above shows a difference in each average percentchange in mass. The experiment when placed in 1°C does not result with a hugedifference in uncertainty than when experimenting at 60°C. This is due to theinconstant masses that resulted during the experiment during high temperatures. At0°C, the uncertainty was ± 0.16, but the uncertainty resulted with ± 2.17 during theexperiment at 60°C.Evaluation: Throughout this experiment, there was one big error which was the size of thedialysis tubing. On the first day of the experiment, the medium size dialysis tubingswere used. However, it was on the second day in which it was discovered that there werethree sizes to the dialysis tubing. So the dialysis tubing used on the first day of theexperiment might have been the different size it was used during the second day of theexperiment. Although there were no major mass differences on the data results from thefirst day of the experiment, there was a possibility that the size of the dialysis tubingmight have changed. This can be improved by carefully examining and by recording thespecific length, width and height for each dialysis tubings. This will prevent suchcareless mistakes since all the specific measurement would be written for the continuingday of the experiment. Along with the size of the dialysis tubing that was used, the accurate length of thetubing might have not all been the same length. As the dialysis tubing was trimmed offwith a knife, the length of each side was not equally straight. This therefore might haveaffected the average percent change in mass as a whole. Also, as the dialysis tubingswere trimmed into pieces, it was not double checked to make sure that they were all thesame sizes. For next time, scissors should be used for more accuracy with the length.Also it would be better if each side of the dialysis tubings are marked so that the tubingswould be trimmed equally on both sides.
Honori Yamada Bio 2 Sept/2/10 As it is shown in table 3, another error that might have affected the inconstantdata results was the stability of the given temperatures. As a dialysis tubing was placedin salt water for 10 minutes, there were some difficulties in keeping the temperaturestabled. A thermometer was placed in the beaker to keep the temperature stabled, but attimes the temperature increased and decreased by 1°C. So from the instability ofkeeping the temperature at the same degree, the percent mass of the tubing might havebeen affected overall. To prevent this from happening next time, an instrument knownas the constant temperature bath should be used to keep the temperature at a steadydegree. This we surely prevent the solution from increasing or decreasing thetemperature and therefore will not affect the overall result of the experiment. Tissue papers were used to dry and rescale the dialysis tubing five times for eachtrial. As drying the tubings were rushed through so that time would not have affectedthe results, properly drying the dialysis tubings each time was another error. Since somemeasurements were too different from the other five measurements in the trial, it wasconsidered as an outlier. This was due to how inaccurate the dialysis tubings were driedeach time as some bits of water might have been still left in between the dialysis tubingclamps. For a better accurate experiment, more time in drying each tubings should bedone. One person should be the dryer who constantly paper towel dries each dialysistubing the same way precisely.Weakness How/what SolveSize of dialysis tubing Thought there was only Look to see if there are any type of dialysis tubing other sizes by width of the (width) dialysis tubing and recond it somewhere on dataLength of dialysis Trimmed with knife and Mark each end sides of thetubing used ruler dialysis tubing and cut with scissorsInstability Temperature Used thermometer to keep Use instrument known as eye on exact temperature constant temperature bathMeasurement error Used tissue paper to Accurately take more time quickly dry out water and dry each tubing in surrounding the tubings between small edges/gaps▲Table 3: The different weaknesses that appeared during the experiment and how itshould be solved is shown The Effect on Osmosis with Temperature