Osmosis - Where is the isotonic point of a potato chip?

GCSE: Biology

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When a cell gains water by osmosis the cytoplasm pushes against the cell wall. A plant cell that has developed an internal pressure is called turgid.
A cell is flaccid if it is placed in a concentration that has a lower water potential than it. It loses water due to osmosis and the cell decreases in volume. Eventually the cell contents has shrunk so much that the membrane and cytoplasm split from the cell wall and gaps appear. This is called plasmoyed.
The isotonic point is where the concentrations of water inside and outside the potato cells are equal. No osmosis occurs at this point there is no change in the length, volume or mass of the potato, as the net movement of water is zero.

To find the isotonic point we can place a potato chip in several solutions each with different amounts (different concentrations) of sugar solution. When after a while the weight of the chip is the same as it was before with no water lost or gained we will record this point as it is the isotonic point of the chip.






















Prediction

I predict that the isotonic point will fall somewhere between 2M and distilled water. My preliminary work has enabled me to predict this yet it wasn’t detailed enough to be more specific. If we place the potato chips in distilled water I expect them to increase in length and weight as the water potential outside is greater than inside meaning the potato takes in water through osmosis. It travels from an area of high concentration to an area of low concentration. If we place the potato chips in sugar solution I expect the weight and length of the chip to decrease as the water potential outside is less meaning the potato loses water through osmosis. We want to test the potato chips in different strength solutions to find the isotonic point where there is no net movement, the water potential inside and out of the potato is equal.
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