How Does A Cell Membrane Work?

Movement of Sucrose Across Plant Cell Membranes

The cell membrane is a barrier between the internal and external environments of a cell. Water molecules are the sole molecules that can freely move across the cell membrane. This process is known as osmosis, and it is stated as being the net movement of water across a cell membrane. For this study, we obtained potato tubers and immersed them in different solutions of sucrose concentrated water. The purpose of this study was to determine the osmotic concentration of potato tuber cells by their change in mass.

(Ha:) It was hypothesized that the final mass of the potatoes immersed in the solution of sucrose would change, due to the net movement of water. We also hypothesized that the mass of the potatoes immersed in the distilled water containing no sucrose would be greater. We came to this hypothesis by making reference to the fact that the sucrose within the potatoes would be greater than that of the water. Thus, the water would attempt to pass through the cell membrane to equal the external environment with the internal environment of the potatoes. This process would be reversed (water leaving the cell, due to higher concentration of sucrose outside the cell) as the concentration of sucrose became greater. (Ho:) If there were to be no effect on the cells of the potatoes, our hypothesis was that there would be no change in the mass of the potato because the solution, as well as the potato would be in an isotonic environment.

Six potato tubers were obtained, each cut to 4 cm. All six cylinders were placed on a moistened paper towel, and each was removed to be thinly sliced with a razor blade. Each sliced potato tuber was rinsed and blotted dry, then placed in an empty weight boat to be weighed on the balance. The balance was tared before each tuber was weighed. After each tuber was weighed, the mass was recorded on a chart. Each tuber was placed in a solution of sucrose and water, each solution containing a higher solution of sucrose than the next. The first contained no sucrose, just distilled water. Each solution that followed contained a molarity of 0.1, 0.2, 0.3, 0.4, and 0.5 of the sucrose.

We found that the greatest change in mass took place in the solution containing a molarity of 0.5 sucrose concentrations. The smallest change took place in the solution containing a molarity of 0.2 sucrose concentrations. The solution containing 0.2 sucrose concentrations was the closest to being an isotonic environment.

The results supported our hypothesis that the mass of the potato tubers would change, according to the sucrose solution it was immersed in. In the solution containing no sucrose, the tuber did gain mass as the water moved across the cell membrane to attempt to equalize the environments. There was a change in each solution, the solution that was closest to an isotonic environment contained 0.2 sucrose concentration. The tuber in the solution containing the greatest amount of sucrose concentration (0.5), lost the most water weight of all the tubers. This happened due to the concentration of sucrose being greater outside of the potato cells. The water within the cells left passed through the cell membrane to attempt to equalize the environments. The reaction of this cell is the opposite of the cell immersed in distilled water containing no sucrose.

Thus, we concluded that as the sucrose concentration intensified, the potato cells lost water weight due to their attempt to equalize the internal/external environments.

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