The Effect of Sucrose on Liver Cells

Prediction

Osmosis is the "net movement of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane." The diagram below illustrates the process of osmosis. (See Figure 1)

As shown by the Figure 1, water molecules move from a region where there are many water molecules to an area of less water molecules.

This means that in the potato cells, water molecules will move in or out of the cell depending on the concentration of the sucrose solution and the water potential that the cell has. The process of water molecules moving out a cell is called exosmosis and the process of water moving into a cell is called endosmosis. Endosmosis occurs when the water potential inside the cell is lower than the water potential outside the cell.

Figure 2 illustrates the processes that will occur in the cells.

As varying concentrations of sucrose solution will be used, ranging from 0.0M to 1.0M the amount of water molecules that passes in or out the potato cells and in or out the sucrose solution will vary with concentration. I predict that at 0.0M where there are no sucrose molecules and just water molecules, water will move into the cell as the solution has a higher water potential than the potato cell.

From my preliminary results I can see that at concentrations of 0.0M and 0.2M of sucrose solution there was a positive increase in mass as for 0.0M the average percentage change in mass was 7.47% and for 0.2M there was an average percentage change in mass of 3.85%. This increase in mass is due to water moving into the cells (endosmosis). There will be a point where water will stop moving in the cell as the water potential in the sucrose becomes equal to the water potential in the potato cells. Therefore as the concentration of sucrose increases from this point, less water will diffuse out the cells as there is higher water potential in the sucrose solution then at high concentrations of sucrose. At concentrations of 0.4M and higher there was a decrease in mass as the concentrations above 0.2M showed a negative average percentage change in mass with 0.4M having a -0.53% change in mass and the following increasing in the loss of mass. There was a loss in mass because there is lower water potential in the sucrose solution and a high water potential in the potato cells so water molecules move out of the cells and into the sucrose solution by exosmosis.

The process of osmosis has an effect on the potato tissue as a loss or gain of water will affect the tissue.

At concentrations of 0.0M and 0.2M of sucrose solution water molecules are moving into the potato cells. Therefore the cells are increasing in mass and overall the tissue increases in mass. The potato tissue will increase in size as water molecules entering its cells will cause the cells to increase in volume and become turgid.

From my preliminary results, after concentration of 0.4M there was a loss in mass of the potatoes. This shows that exosmosis is occurring as water is moving out the cells causing a drop in mass. This will cause the potato tissue to become flaccid as the cells lose their shape.

The condition of the potato cells will be different before and after 30 minutes of being in the sucrose solution.

At low concentrations of sucrose solution, where the water potential is higher than most of the water potential of the cells, water will move into the cells. At 0.0M many water molecules will move into the cells but as the concentration gets higher, less water molecules will move into the cell. As water moves into the cell, it increases the volume of the cell, and also causes the protoplast (the living part of the cell wall) to push against the cell wall, which increases the pressure against the cell wall. This is the pressure potential and it increases the water potential of the cell until the water potential of the cell is equal to the water potential outside the cell. The cell wall prevents the cell from bursting so instead the cell becomes turgid as the protoplast pushes against the cell wall.

Figure 3 shows the condition of the cell before and after 30 minutes of being in a solution of 0.0M and 0.2M

At concentrations of sucrose solution where the water potential is higher in the cell then in the solution, water moves out of the cell and into the solution. The loss of water from the cell causes the protoplast to shrink and the cell becomes flaccid.

I predict that at 1.0M the cells will become plasymolysed as either all the water or most of the water in the cells have left by exosmosis and therefore the protoplast as shrunk so much that it is not exerting pressure on the cell wall and the cell is plasymolysed. Eventually cytorrhyis can occur and this is the complete collapse of the cell wall within plants due to a loss of water.

Figure 4 shows the condition the potato cells in solutions of 0.8M and 1.0M before and after 30 minutes of being in a solution of high sucrose concentration.

Sucrose does not diffuse into the cell and sucrose in the cells does not diffuse out of the cell due to the cell membrane. The phospholipid bilayer that makes up the cell membrane is selectively permeable membrane. This means that only certain molecules can enter and exit the cell and water is a molecule that can freely diffuse through the cell membrane. Water is a small molecule that can freely diffuse through the cell membrane and it is why a change in water potential affects the cell. However, sucrose doesn't diffuse through the membrane because sucrose is a bigger molecule than water and thus cannot pass through the phospholipid bilayer. Sucrose is transported into the cell by facilitated diffusion.

Plan

The graph drawn from the preliminary results show that at a concentration of 0.4M the percentage change in mass is 0%. Using graph 2 I can determine the water potential at this concentration. The water potential is -1150kPa but this is not the water potential of all the cells as each cell in the potato piece will have different water potential and the water potential may vary greatly. Below are the results of a group of 11 results for the concentration at which there is 0% change in mass from the experiment:

0.26M

0.34M

0.36M

0.32M

0.25M

0.4M

0.5M

0.33M