Explaining osmosis:
When you put an animal or plant cell into a liquid containing water one of three events will take place,
1. If the solution surrounding the cell has a higher water concentration than the cell (a very dilute solution) the cell will gain water by osmosis.
Water molecules are free to pass across the cell membrane in both directions, however, more water will come into the cell than will leave. The end result is that water enters the cell. The cell is likely to swell up.
2. If the solution is exactly the same water concentration as the cell there will be no movement of water across the cell membrane.
Water crosses the cell membrane in both directions, but the amount going in is the same as the amount going out, so there is no overall movement of water. The cell will stay the same size.
3. If the solution has a lower concentration of water than the cell (a very concentrated solution) the cell will lose water by osmosis.
Water crosses the cell membrane in both directions, but this time more water leaves the cell than enters it. This causes the cell to shrink.
Osmosis in plant cells:
Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall stops them from bursting. Plant cells become "turgid" (turgid means swollen and hard) when they are put in dilute solutions. The pressure inside the cell rises; eventually the pressure is so high that no more water can enter the cell. This liquid works against osmosis. Turgidity is very important to plants as this is what makes the green parts of the plant "stand up" into the sunlight.
When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become "flaccid"; this is the exact opposite of "turgid". If you put plant cells into concentrated sugar solutions and look at them under a microscope you would see that the contents of the cells have pulled away from the cell wall and shrunk. When plant cells are placed in a solution that has exactly the same osmotic strength as the cells, they are in a state between turgidity and flaccidity. We call this plasmolysis. Although their cells are not plasmolsysed, they are not turgid and so the leaves are not held into the sunlight.
Prediction:
I predict that if the water concentration is higher than the concentration of water inside the potato, then the potato will become stiff, hard and enlarged, as it will take water in by osmosis. The potato should become heavier as a result of this. However, if the water concentration inside the potato is greater than outside the potato the water that was in the potato will gradually move out of the potato by osmosis. Therefore the potato will become soft, floppy and will shrink, making the potato loose weight. If the concentration is the same inside and outside of the potato then hopefully no changes should be made to the potato and its weight should stay the same. I have based my prediction according to the theory of osmosis.
