Osmosis and Potato Tuber

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Estimating Osmolarity by Change in Weight


Optimum water content for normal physiological processes in plants is crucial. In order for normal activities to take place, the amount of water relative to osmotically active substance (OAS) in cells must be maintained within a reasonable range. The one way to estimate optimum water content is to find osmolarity of plants cells. Osmolarity can be indirectly measure by comparing change in weight and volume when plant cells are incubated in OAS solution of known molarity. Estimated osmolarity of plant cells is the molarity of solution at which weight or volume of the plant cells does not change, means there is no net loss or gain of water.


This study shares the results of an effort to understand diffusion and osmosis in general. It focused more into osmosis in plants cell, and how to indirectly measure osmolarity in potato tuber tissue.

Osmosis is the diffusion specifically of water across a membrane. Diffusion occurs when certain substance, such as an ion, is more concentrated on one side of membrane. If the membrane allows this ion through, the ions will move from the more concentrated side to the less concentrated side until reaching equilibrium. A cell’s tonicity indicates in which direction is the net flow of water and is based on the ionic content of the cell. A cell which is isotonic has an ionic concentration identical inside the membrane and out. Since the cell is at equilibrium, there is no concentration gradient and the flow of water in is equal to the flow of water out. A cell which is hypertonic has a higher concentration inside the cell than out. This causes a concentration gradient across the membrane which results in a net flow of water into the cell. A cell which is hypotonic has a lower concentration and therefore water will flow out of the cell. The tendency of water movement from hypotonic solution through the membrane into a hypertonic solution can be prevented by...
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