Laura Pottle
The Affect of Time on the Rate of Osmosis
Aim: To see how the amount of time affects the rate of Osmosis on a potato.
Prediction: I predict that during the experiment the potato will shrink as the concentration of the water decreases; we will find this out by measuring the potatoes mass after a certain amount of time.
Background Knowledge: Osmosis and dialysis are of prime importance in living organisms, where they influence the distribution of nutrients and the release of metabolic waste products. Living cells of both plants and animals are enclosed by a semi-permeable membrane called the cell membrane, which directs the flow of liquids and of dissolved solids and gases into and out of the cell. The membrane forms a selective barrier between the cell and its environment; not all substances can pass through the membrane with equal facility. Without this selectivity, the substances necessary to the life of the cell would diffuse uniformly into the cell's surroundings, and toxic materials from the surroundings would enter the cell. If blood cells (or other cells) are placed in contact with an isotonic solution, they will neither shrink nor swell. If the solution is hypertonic, the cells will lose water and shrink (plasmolyze). If the solution is hypotonic (or if pure solvent is used) the cells will swell; the osmotic pressure that is developed may even be great enough to rupture the cell membrane. Saltwater from the ocean is hypertonic to the cells of the human body; the drinking of ocean water dehydrates body tissues instead of quenching thirst. In plants osmosis is at least partially responsible for the absorption of soil water by root hairs and for the elevation of the liquid to the leaves of the plant. However, plants wilt when watered with saltwater or treated with too much fertilizer, since the soil around their roots then becomes hypertonic.
