Sherman Chen 3B

Biology 1

Mr. Boyer

Osmosis and Diffusion Lab using Potato Cores

Research Question: Will there be a different amount of water moving in or out of a set of potato cores if they are placed in solutions with different concentrations of sucrose?

Introduction: Osmosis is the movement of water across cell membrane/cell walls through protein channels. The water moves due to water potential of the cells, water moves from an area of high water potential to an area of low water potential. A greater concentration of solutes inside the cell than outside the cell results in a low water potential and the water will respond by moving into the cell. If one area has a great deal of water, it has a high water potential, and if an area has a great deal of solutes, it has a low water potential. In this lab, we were asked to observe the change in mass of potato cores when they are put into different concentrations of sucrose in the solution.

Hypothesis: If the concentration of sucrose in the solutions were higher then there would be more water moving out of the potato cores.

Variables:

Independent Variable – Concentration of sucrose in solutions

Dependent Variable – Mass of the set of potato cores (Movement of water in or out of the potato cores)

Controlled Variables – Number of potato cores in one set; Length of potato cores; Amount of solution

Materials:

·  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

Data Chart:

Potato Group (Concentration of sucrose in solution) / 0.0 / 0.2 / 0.4 / 0.6 / 0.8 / 1.0
Initial Mass (g) / 3.0 0.05 / 3.0 0.05 / 3.0 0.05 / 3.0 0.05 / 3.0 0.05 / 3.0 0.05
Final Mass (g) / 3.3 0.05 / 3.2 0.05 / 2.8 0.05 / 2.3 0.05 / 2.1 0.05 / 1.7 0.05
Percentage / 10% / 6.67% / -6.67% / -23.33% / -30% / -43.33%

Graph of the Results:

Zero: 0.24

Conclusion:

The results we got were expected from our hypothesis. As the concentration of the sucrose increased, the final mass decreased. All of the potato cores’ initial mass was 3.0g and for the first two concentrations of sucrose, 0.0 (distilled water) and 0.2, the final mass increased; this means that the water moved into the potato cores. For the other concentrations of sucrose, the final mass all decreased; this means that the water moved out of the potato cores. My hypothesis was that the higher the concentration, the more water will move out of the potato cores, and I was right. This was not hard to predict because if the solution had a higher concentration of sucrose, it would have a lower water potential meaning that water would flow out of the potato cores and into the solution. In the graph plotted mass in percentage change vs. concentration of sucrose in solution, the best-fit line equation is y = -56.189x + 13.651. The line touches the zero on the x-axis at around 0.24; this number is the water potential for the potato cores because at around a concentration of 0.24 of sucrose in the solution, the mass of the potato cores does not change. The water potential number we got was pretty much similar to other groups except for one where they probably graphed their results wrong. The water potentials for the other groups were: 0.75, 0.34, 0.22, and 0.37. I think there might be some differences in the results of the groups because the time we left our potato cores in the solution were probably all different.

Evaluation/Reflections:

Positives: We were efficient and everybody did their jobs. We got the results we were expecting. We did not have many problems, the experiment went smoothly.

Negatives: We did not wait exactly 24 hours, nor did we measure how long it was we waited until we checked the mass again. First we thought we had different graphs but then I realised I had my concentration of sucrose wrong.

What did I learn: I learnt what osmosis and diffusion was, our experiments generally showed how it works.

Changes: We could have measured the time we waited in between the two times we measured the masses of the potato cores. We also could have been more precise with the measurements like, the length of potato cores and the volume of the solution.