IB Biology SL IA
AP/IB Biology Lab Assessment The effect of various fruit and vegetable cell membranes on their water potential Independent variable: Type of fruit or vegetable. (Produce used: Russet potatoes, Pascal celery, Gala apple, Navel orange, and Imperator carrot). The fruit or vegetable will be placed in six 56. 7 gram cups, ranging with sucrose molarities of O (distilled water), 0. 2, 0. 4, 0. 6, 0. 8, 1. 0, with 5 trials, leading to 30 cups for each produce variable.
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Dependent variable: The water potential of the produce, found by placing the produce in different molarities of sucrose and finding the isotonic state of the roduce with a plotted line graph. Controlled variables: The controlled variables include: The type of produce used: Each variable produce is of the same type. Only Russet potatoes, Pascal celery, Gala apple, Naval orange, and an Imperator carrot were used. The produce to solution ratio. Each sample of produce for each trial was completely submerged in 24 ml (measured with a graduated syringe) of the solution: either distilled water or sucrose of specific molarity.
If the produce was not completely submerged, the measuring of the mass difference and the water potential may not e accurate. The produce, while submerged, received no light. The 56. 7 gram cups were covered with aluminum foil, to prevent the sucrose or water from evaporating. All samples of produce were weighed for initial mass and final mass on a digital gram scale, to prevent human error with a manual scale. The water potential of the produce will be found by marking the percent change in mass with each sample in each solution.
Thus, each sample of produce does not need to be the same weight, as percentages are recorded rather than change in mass. The produce samples will be easured with the digital gram scale, and moved to their designated cups of solution very quickly to prevent the produce cells from becoming flaccid and drying out due to exposure to air. The produce samples will only be transported with tweezers, to prevent oil from hands changing the weight of the sample. Hypothesis: We believe the water potential of the various produce will not vary by more than . 05 bars among the 5 vegetables and fruits.
Each of the produce (carrot, celery, potato, orange, and apple) will gain weight in the solutions of distilled water, . 2-molarity sucrose, and . -molarity sucrose, the produce will gain weight because we are assuming the produce will have a lower water potential than the hypotonic solution, thus osmosis occurs and the produce will absorb water. As the concentration increases to . 6 molarity sucrose, . 8 molarity sucrose, and 1. 0 molarity sucrose, we expect the produce to lose weight, because the produce, being in a hypertonic solution, will have a higher water potential than the solution, forcing water out of the produce cells.
Standards of Comparison: The water potential of the five various types of produce lll De compared to eacn otner, OITTerences In tne produce water potentlal wlll De noted. The water potential of the produce are also compared to the water potential of pure water, O. Materials used: The five produce variables: Russet potato, Gala apple. Imperator carrot, Naval orange, and Pascal celery, obtained from Smiths grocery and Dr. Thirwell’s classroom. The six solutions for each of the 5 produce types: distilled water, 0. 2-molarity sucrose, 0. 4- molarity sucrose, 0. 6-molarity sucrose, 0. 8-molarity sucrose, and 1. 0-molarity sucrose.
The sucrose molarities are calculated and ingredients are measured with a gram scale and a graduated cylinder. 150 56. 7 gram plastic cups to hold a produce sample in 6 solutions, with five trials, and five types of produce. A graduated syringe to measure 24 ml of each solution of sucrose and distilled water A digital gram scale, to weigh the initial mass and final mass of each produce sample A serrated knife for cutting the produce Aluminum foil for covering each plastic cup from light. Tweezers to transport the produce samples to and from cups and onto the scale, to revent hand oils affecting the mass of the sample.
Procedure: 1. Obtain all materials and wash hands 2. Cut 30 pieces of each type of fruit or vegetable, small enough to fit in a 56. 7 gram plastic cup (6 pieces for each trial). 3. Weigh the initial mass of each sample of produce with the digital gram scale and record on a table. 4. Place the recorded samples of produce in their designated cups using tweezers, fill the six cups of each trial with 24 ml distilled water, 0. 2-molarity sucrose, 0. 4-molarity sucrose, 0. 6-molarity sucrose, 0. 8-molarity sucrose, and 1. -molarity sucrose. 5.
Cover each plastic cup with a substantial amount of aluminum foil to prevent the evaporation of the solution. 6. Let the 30 cups for each of the 5 types of produce sit for two days. 7. After two days, remove the aluminum foil, and record the final mass of each sample of produce using the digital gram scale, and transporting the fruit or vegetable with tweezers. Remove excess liquids of the sample by dabbing it on a paper towel. 8. Record the final masses on a table 9. Record the percent change in mass for each cup, find the averages and standard eviation for the 6 solutions for each fruit or vegetable variable. 10.
Plot the averages for each fruit or vegetable with a line graph and record where the percent change in mass intercepts the x-axis (molarity of sucrose)- where the graph intercepts the x-axis represents the molar concentration of sucrose with a water potential that is equal to the produce’s water potential. 11. Record each of the produce’s water potential. Compare and contrast. Qualitative Observations: At tne start 0T tne experlment, all produce appeared In normal conaltlon, ana all 0T he sucrose solutions had settled and looked normal, although the 0. 2-molarity sucrose had a small amount of mold in the interior of the bottle.
In the middle of the experiment, all produce samples were placed in their correct cups and were covered with aluminum foil. In order to keep the experiment controlled, we did not remove the aluminum foil until the produce had soaked for two days and was ready to be weighed. At the end of the experiment, we noticed a majority of the produce, especially apples, became soft and turgid in the solutions of distilled water, 0. 2- molarity sucrose, and 0. -molarity sucrose, as following to the fact that we noticed the majority of the produce gained weight (in grams) in those solutions.
We also noticed produce, especially potatoes, in the solutions of 0. 6-molarity sucrose, 0. 8- molarity sucrose, and 1. 0-molarity sucrose grew mold, which was peculiar because every potato sample in the 1. 0-molarity sucrose lost an average of 25 percent in mass. Analysis of data: As shown by the graph and tables, the averages of percent change in mass showed the potato samples increased mass in the control, distilled water, and 0. 2-molarity sucrose. The potato samples also lost considerable mass in 0. 4-molarity sucrose, 0. 6- molarity sucrose, 0. 8-molarity sucrose, and 1. 0-molarity sucrose.
The data is unusual, as on average, the potato samples gained 3. 3% of mass in 0. 2-molarity sucrose, and only 2% gain in mass in distilled water. What may explain why our potato sample data is peculiar is that the standard deviations for this variable are very high. The standard deviations for the potato samples are as following: 19. 9, 4, 2. 6, 9. 6, 5. 8, and 6, meaning the percent change in mass for each trial varies greatly compared to the verage. By graphing the averages for potato samples in a graphing calculator, we found the potato cells’ water potential is approximately 0. 5 bars, which would mean potential energy of water is 0. 25 bars per unit volume of potato, compared to pure water. Carrots, on average, gained percent in mass in solutions of distilled water, 0. 2- molarity sucrose, and 0. 4-molarity sucrose, with low standard deviation of 0. 6, 1, and 3, meaning the carrot’s water potential of . 43 bars may be accepted. The carrot samples also lost percentage in mass in the solutions of 0. 6-molarity sucrose, 0. – molarity sucrose, and 1. 0-molarity sucrose, but the standard deviations of 4, 13, and 13. 7 show that these data points may not be accurate and are not proven.
The orange samples on average gained percentage in mass in the solutions of distilled water, 0. 2-molarity sucrose, 0. 4-molarity sucrose, 0. 6-molarity sucrose, and 0. 8- molarity sucrose and lost a small amount of mass in 1. 0-molarity sucrose. The orange variable data surprised us; even though our hypothesis states that we predicted each variable to have similar water potentials, out of all the produce we would expect the range to have the highest water potential due to its somewhat saturated form. By graphing the average points on the graph, we found the water potential of the Navel orange is approximately . 4 bars, a very low water potential compared to pure water, wnlcn Is u I ne stanaara aevlatlons Tor our orange sample data were . / 1 . 1, and 3. 6 ranging in order from distilled to 1. 0-molarity sucrose. By viewing the standard error of the means (on graph) and the standard deviations, the orange’s water potential of . 94 bars may be supported by the data. The celery samples on verage gained mass in distilled water, 0. 2-molarity sucrose, and 0. 4-molarity sucrose, and lost mass in solutions of 0. 6-molarity sucrose, 0. 8-molarity sucrose, and 1. 0 molarity sucrose.
The standard deviations, in order from distilled water to 1. 0- molarity sucrose are as followed: 1. 5, 5. 8, 3. 3, 8. 3, 2. 3, and 5. 6. By the graph on celery trial averages, the water potential of celery is calculated to be approximately . 46 bars. The average percentage change in mass for the apple samples showed that they gained weight in solutions of distilled water, 0. 2-molarity sucrose, and 0. 4-molarity ucrose; the apple samples on average also lost weight in solutions of 0. 6-molarity sucrose, 0. 8-molarity sucrose, and 1. 0-molarity sucrose.
By the graph, the water potential of the apple samples are calculated to be . 51 bars, and due to the low standard deviations (2. 6, 3. 2, 2. 1, 1. 7, 1. 4, 4. 7) of the variable when it intercepts the x- axis, the water potential of approximately . 51 bars may be proven. Possible experimental errors: Due to the fact that all the produce in the classroom were used, the produce used in the experiment came from two different sources, possibly leading to slight ifferences in water potential of each sample. The sucrose solutions were replaced in the middle of experimental setup.
Although the same recipe was used for both batches of the various sucrose molarities, there was possible ratio difference in the second group of sucrose solutions, which may have lead to inaccurate data. After the produce samples were soaked in their specific solutions for two days, when finding the final mass of the samples, occasional residue was not completely removed with a paper towel, possibly leading to inaccurate data of final mass. Two different digital ram scales were used during the experiment, which may have caused a slight difference in the mass recordings.
While transporting the produce from the scale into their cups and then adding the solutions, some produce were exposed to dry air longer than others, possibly changing the data. Some of the produce used, especially the potatoes, were much older than others, which may have led to some of the produce cells already dead, and may be the cause of the potatoes’ varying data. Measuring the mass of the produce samples was very hurried and possible mistakes in the writing of data are likely possible. Conclusion Our hypothesis, Water potential of the various produce will not vary by more than . 5 bars among the 5 vegetables and fruits. Each of the produce will gain weight in the solutions of distilled water, . 2-molarity sucrose, and . 4-molarity sucrose. As the concentration increases to . 6-molarity sucrose, . 8-molarity sucrose, and 1. 0- molarity sucrose, we expect the produce to lose weight’ is not supported by our experimental data. Although produce such as the carrot, celery, and apple samples showed the trends stated by the hypothesis, not every variable showed these trends, which is hat we hypothesized.
The water potentials calculated for the produce variables are as followed: Potato . 25 bars, carrot . 43 bars, celery . 46 bars, apple . 51 bars, and orange with . 94 bars. The water potentials calculated vary significantly as opposed to tne nypotnesls, out tne water potentlals are not completely accurate high standard deviations in each of the produce variables. Further experimentation: Oue to some For improving this experiment of ‘The effect of various fruit and vegetable cell membranes on their water potential’ several improvements should be considered:
Possibly, test the water potential of various vegetables specified in one family, such as the marrow vegetable family (cucumber, melon, pumpkin, squash, mallow, and courgette). By testing one family, the experiment is more specified as opposed to the hundreds of different types of various fruit and vegetables. Testing one specific family of vegetables may also lead the data to be less varied and unsupportive. Make sure the mass of the produce sample measured is accurate by weighing it more than once and removing all excess residue Specify a specific part of the produce, which ill be experimented, such as produce cores or skin.
View the produce cells before and after soaked in specific sucrose molarities under a microscope to compare their form before and after osmosis. After these specific variables of sucrose molarities, possibly vary the sucrose molarities too, . 1, . 2, . 3, . 4, . 5, . 6, . 7 . 8 . 9, and 1. 0 to see more specific trends in data Make enough of the sucrose molarities so replacements are not needed, thus, less potential in mistakes while making the sucrose solutions Make note of the temperature in Celsius: thus water potential may be calculated on paper, which is more accurate