Jacob Dyer 3B
Mr. Boyer
Osmosis and Diffusion Lab
Research Question
Will there be a different amount of water moving in or out of potato cores if they are placed in solutions with different concentrations of sucrose?
Introduction
In this lab we observed osmosis across cell membrane and cell walls in protein channels in potato cells. Osmosis occurs when there is a difference in water potential. The water always goes down a concentration gradient. If part of a cell has a higher amount of water there is higher water potential while if there is a part with a higher amount of solutes, there is lower water potential. For this lab, we are observing osmosis happening in potato cores with sucrose solutions. We will observe the change in the mass of the potato cores as they are put in contact with solutions of sucrose with different concentration levels.
Hypothesis
If the concentration of sucrose increases in the solution, then the water will move out of the potato core and the mass and the percentage change of the mass of the potato will decrease. As there is more sucrose in the solution the mass of the potato decreases because the water in the potato goes out to create equilibrium and an isotonic solution.
Variables
Independent Variable – Concentration of sucrose in the separate solutions
Dependent Variable – Mass of the potato cores (amount of water in potato core)
Controlled Variables – Number of potato cores added to each solution, size of the potato cores (length), volume of solution in test-graduated cylinder, time allowed for the potato cores to stay in the solution (24 hours)
Materials:
· You will be working in groups of 4 if at all possible to share the work load (2 buddy groups)
· Potato cores (4 per condition)
· Sucrose solutions (.2, .4, .6, .8, 1.0 )
· Distilled water
· Electronic balance
· Plastic weighing tray
· Plastic cups (6)
· Graduated cylinder (50 ml)
· Scalpel
· Marking tape
· Blue tweezers
Procedures
· Using marking tape, label 6 cups with the following solution types (.2, .4, .6, .8, 1.0 and Di water)
· Place approximately 50 ml of the various solutions, each cup receiving a separate solution. Suggestion, measure the di water with the graduated cylinder, and fill the other cups to the same level
· Obtain 24 potato cores and cut them to equal sizes (about 2.5 cm). All the cores you use must be the same length
· Divide your 24 cores into 6 groups and gently blot them dry with a paper towel
· Using the electronic balance and plastic weighing tray mass (weigh) each group of potato cores and record the data in a table that is labeled with a detailed title and which provides the error measurement of the electronic scale. MAKE SURE TO TARE THE TRAY. The table should record the type of solution in the cup and the mass of the potatoes in the cup.
· Place the potato core sets in their appropriate cup and place in Mr. Boyer’s back prep room in the fume hood that is labeled with your block (3B or 4B).
· PS make sure to indicate on your cup your group number, Mr. Boyer will assign group numbers during the lab
· 24 hours later (app) you will need to come and measure the mass of your potato cores. To do this you must pore off the fluid in the cup and use the plastic blue tweezers remove the cores, blot them dry just as you did in the set up phase and final measure them using a plastic weighing tray. MAKE SURE TO TARE THE TRAY. Record your potato group mass on your data chart.
· Finally dump your potato cores in the trash and wash and dry your equipment (cups, tweezers and return them to their stations
· Calculations. For each setup (all 6) you will need to calculate a percent mass change. To do this you will use the following formula (final mass-initial mass)/initial mass x 100. You will need to record this data in your data table as well. Make sure to keep track of the positive and negative changes if they occur
Sucrose Concentration Level / Initial Mass / Final Mass / Percentage Change0 / 3.0 g ±0.05 / 3.3 g ±0.05 / 10%
0.2 / 3.0 g ±0.05 / 3.2 g ±0.05 / 6.67%
0.4 / 3.0 g ±0.05 / 2.8 g ±0.05 / -6.67%
0.6 / 3.0 g ±0.05 / 2.3 g ±0.05 / -23.33%
0.8 / 3.0 g ±0.05 / 2.1 g ±0.05 / -30%
1.0 / 3.0 g ±0.05 / 1.7 g ±0.05 / -43.33%
Zero = 0.24 (Note: the zero is for the best fit line)
Conclusion
This lab was mostly consistent with my educated guess or predictions included in my hypothesis. With all of our results, as the concentration of the sucrose increased, the percentage change for the mass of the potato decreased quite stably (there were no strange outliers). However as the concentration of the sucrose increased, the mass did not necessarily decrease as shown with the sucrose concentration levels 0 and 0.2. This lets us infer that potato cores contain a small amount of sucrose, more than the 0.2 and 0 mols of sucrose in the solutions for the solution to have greater water potential than the potato core. This is why water and the overall mass of the potato core increased in the 0 and 0.2 concentration levels of sucrose, to achieve equilibrium. This part of the experiment was not consistent with my hypothesis, If the concentration of sucrose increases in the solution, then the water will move out of the potato core and the mass of the potato will decrease, because as the concentration of sucrose increased from 0 (distilled water) to 0.2 mols, the mass of the potato core increased instead of my predicted decrease showing that there was more sucrose in the potato core than the 0.2 mols of sucrose in the solution. However, the rest of the experiment was consistent with my hypothesis as when the concentration level of the sucrose increased, the mass of the potato core decreased accordingly. An example of this is shown with the percent change of mass with the 0.6 concentrations level of sucrose having a lower mass than both the previous concentration and the original mass (going from 3.0 g to 2.3 g and falling from -6.67% change to -23.33%). Our experiment proved that even though potatoes contain sucrose (more than 0.2 mols), they still have a lower water potential than sucrose solutions starting from 0.4 mols (at the most) as shown with the intake of water with the 0.2 mol solution and the release of water in the 0.4 and higher concentration levels of sucrose. In reference to the graph (Sucrose concentration level vs. percent change in mass of potato core), the equation of the best-fit line is y = -56.18x + 13.65 therefore X=0.24 therefore the water potential for the potato core is 0.24 mols of sucrose. This explains the reason why when the solution concentration level is 0.2 mols of sucrose, the mass of the potato core increased. The water potential was higher in the potato core therefore the lower water potential needed to push water into the potato to make it in equilibrium with the 0.2 concentration sucrose solution. This also explains why at 0.4 mols of sucrose solution, the mass of the potato decreased as there was higher water potential in the solution so the cell pushed water out to create equilibrium with the 0.24 water potential potato and the 0.4 water potential solution. While conferring with the other groups, we got their zeros or potato core water potentials which were as follows, 0.75, 0.34, 0.22, 0.37, and 0.24 (our group). Most of these pieces of data fit with my experiment because they are in-between 0.2 and 0.4 mols of water allowing potentially a very close experiment to happen. However, the 0.75 concentration level of sucrose as the water potential of the potato core was seemingly wrong because it was not consistent with my results saying that the potato core had a higher water potential than 0.2 and a lower water potential than 0.4. This outlier could come from a mistake graphing or an observation mistake by the group.
Evaluation/Reflections:
In this lab, I felt as if my group excelled in performing the practical experiment, as we were able to achieve our goals in the lab. I felt as though the lab itself, the way we executed it by following the instructions put in place was quite simple and as a result, the lab went quite smoothly. Some negative aspects of our lab that we could have done better would be to control our controlled variables better. This would include making sure the timing for the experiment was exact, making sure each set of potato core was able to control the 24 hour time in the solution (using a timer). Another variable we could have controlled would be the volume of the solutions in the cups as we filled one cup with 50 ml of the solution and ‘eyeballed’ the rest of the cups thus making it inaccurate. Another problem that occurred was during the graphing; we had trouble figuring out the method of creating the graph the way we needed it to be (not a large problem, just an example of not knowing how to graph this kind of graph e.g. with the equation on the graph). Through this experiment, I was able to experience and observe firsthand, the process of osmosis and finding the water potential of the potato cores. It gave me great practice and gave me a good recap of osmosis and diffusion, what they are and how they work and their real life applications. If I could have done this experiment another time, I would have used a timer to time the 24 hours in between each observation of the potato cores and try to be more accurate in measurements (the volume of the solution – measuring instead of eyeballing). Also, something I would have liked to do would be to do the same experiment except to try more concentrations levels closer to the potato cores water potential so we could get real data of the water potential (try 0.23 and 0.25 concentration of sucrose etc.) thus making our observations on the water potential of the potato core more accurate.