To test the effect on potato tubers in different percentages of saline and water

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Coursework on Osmosis

Aim

    To test the effect on potato tubers in different percentages of saline and water

Investigative Research

                               

        Osmosis, in botany and chemistry, the flow of one constituent of a solution

through a membrane while the other constituents are blocked and unable to pass

through the membrane. Experimentation is necessary to determine which

membranes permit selective flow, or osmosis, because not all membranes act in this

way. Many membranes allow all or none of the constituents of a solution to pass

through; only a few allow a selective flow. In classic demonstration of osmosis, a

vertical tube containing a solution of sugar, with its lower end closed off by a

semipermeable membrane, is placed in a container of water. As the water passes

through the membrane into the tube, the level of sugar solution in the tube rises

visibly. A semipermeable membrane that may be used for such a demonstration is

the membrane found just inside the shell of an egg, that is, the film that keeps the

white of the egg from direct contact with the shell. In this demonstration, the water

moves in both directions through the membrane; the flow is greater from the vessel

of pure water, however, because the concentration of water is greater there, that is,

fewer dissolved substances exist in this solution than in the sugar solution. The level

of liquid in the tube of sugar solution will eventually rise until the flow of water from

the tube of sugar solution, under the influence of hydrostatic pressure, just equals the

flow of water into the tube. Thereafter, no further rise in level will occur. The

hydrostatic pressure establishing this equality of flow is called osmotic pressure. A

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variety of physical and chemical principles is involved in the phenomenon of osmosis

in animals and plants.

Freezing is an alternate method, based on the different freezing points of fresh and

salt water. The ice crystals are separated from the brine, washed free of salt, and

melted into fresh water. In another process, called Reverse Osmosis, pressure is

used to force fresh water through a thin membrane that does not allow the minerals

to pass.

 Another important property of a solution is its ability to exert osmotic pressure. If two

solvents are separated ...

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