Effects of Molarity Change of Potato Cell: Lab Experiment

Lab Report

Theory:

The random movement of water molecules from a high water potential gradient (high concentration) to low potential gradient (low concentration) through partially permeable membrane is called osmosis. In osmosis, the solute cannot pass through the partially permeable membrane but the solvent can because it only allows certain material to pass through.(Pickering Ron) An example of the effect of osmosis are the pruned fingers that we get when our hand is soaked in water for a long time and the skin looks bloated. (Kulbhushaan Raghuvanshi). If osmosis occur in red blood cells (animal cells), they burst because of having no cell wall as water enters the cell when placed in a solution with high concentration of water, and shrink when placed in a solution with low concentration of water. If osmosis occur in plant cell, the plant cell swells but doesn’t burst due to the strong cell wall when placed in a solution with low concentration of water. (Brittani Sponaugle)

Planning:

I conducted an experiment in which we experimented that what is the effect of molarity on change of mass of potato cell? We took 6 similar sizes and lengths of potato and then recorded each of their masses using measuring scale. Next we put them into solutions with different molarities like 0.0, 0.2, 0.4, 0.6, 0.8 and 1. And after a while we took them out and again weighed them. We calculated the percentage change in mass by dividing change in mass over initial mass and multiplying it by 100. I predicted that if the potato cells are placed in solutions with higher molarity, it will lose mass and if the potato cores are placed in solutions with low concentration of NaCl, the more mass it will gain. In this experiment, the independent variable was the molarity of NaCl solution and the dependent variable was the percentage change in mass. The controlled variables were the temperature, size of potato, time spent in solution and the amount of solution.

Analysis:

The results I got were according to the prediction I made. My results showed that if the potato was placed into solution with 0 molarity (distilled water) it gained mass while the potato’s that were put into solutions with low water concentration (higher molarity) it lost mass. I conclude that this was because when the potato cell was placed in distilled water, the concentration of NaCl (solute) was higher inside the cell than outside the cell while the concentration of solvent (water) was higher outside the cell than inside the cell. Thus the water moved inside the cell as the solute could not pass the partially permeable membrane increasing the mass of the cell. Similarly, when the potato cell was placed in solution with higher molarity, the concentration of NaCl was higher outside the cell and lower inside the cell whereas the concentration of water was higher inside the cell and lower outside the cell. So the water moved out of the cell from higher concentration to lower concentration and the cell lost mass.

We conducted our experiment several times and calculated the average for more accurate results. The data table showed that if the potatoes cores are placed in distilled water, it has more mass at the end whereas if it is placed in solutions with high molarity, it lost mass so it was according to the hypothesis I made. And I believe my results were right as I got a graph with both positive and negative values that proves the gain and loss of the mass of the potato cell. I got a curve on my graph and there were some points that didn’t fit into my best fit line but that is because of the mistakes I made or little inaccuracies occurred during the experiment. The anomalies in the graph maybe occurred because the potato cores were not fully emerged in the solutions as they could float. Variations could have been because I didn’t cut all potatoes to right dimension and would not have got them all in exactly same sizes or as I didn’t put all the potatoes together at the same time so the length of the time potatoes were in the solutions differed. The difference may have been also caused because of not taking exactly the same amount of volume of the solutions, there could be slight ups and downs (a milliliter or two difference), so therefore some beakers may have had tiny amounts of solutions more or less as compared to other beakers. The time taken for osmosis could also have been affected because of not peeling the potatoes completely. (Seonlim Lee)

Evaluation:

I could improve my experiment by using more solutions with different molarities like 0.0, 0.1, 0.3, 0.4 and etc. I would try to make sure that all potato cores are fully submerged into the solutions by using some sort of fabric or cover to push the potato cells completely into the solution. I could make use of some sort of machines to cut all the potato pieces into same length and to get same amount of solutions, I could have used digital and advanced machines that would pour the exact amounts of solutions avoiding the inaccuracies. I would have allowed more osmosis to occur by increasing the time duration of the experiment that would have produced better results. And to allow osmosis to occur quickly and efficiently, I would make sure to peel the potatoes completely. (Seonlim Lee)