Investigating Osmosis in Potatoe Tissue

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Investigating Osmosis in Potatoe Tissue

To find out how the concentration of sucrose solution affects the rate

of osmosis in a potato and what happens to the length and mass of the


What is osmosis?

Osmosis is the movement of the water molecules across a partially

permeable from a region of high water concentration to a region of low

water concentration.

Osmosis is a special case of diffusion

The biochemical process in living cells always takes place in a

solution. A solution is made up of a solvent (the dissolving fluid)

and solute (the particles dissolved in the solvent). In living

organisms, the solvent is water and the solution is called aqueous


Living cells are separated from their surroundings by the partially

permeable cell surface membrane. The contents of the cell, the

cytoplasm, are one aqueous solution and the surroundings of the cell,

for example pond water, is another aqueous solution. If the two

solutions do not have the same concentration of various substances,

molecules may move away from one to the other by diffusion, if the

membrane is permeable these substances. To summarise osmosis:

The diffusion of water molecules, down a water potential gradiant

across a partially permeable membrane.

Cells and osmosis

A cell is surrounded by a partially permeable membrane, and water may

cross the membrane easily. If cell is placed in a solution of lower

water potential, water leaves the cell by osmosis. If the cell is

placed in a solution of higher water potential, water enters by


Plant cells and osmosis

When water enters a plant cell by osmosis the cytoplasm will swell,

but only until it pushes against the cellulose cell wall, as shown

below. The strong wall stops the cells from bursting. We say that the

cell is turgid. A plant cell will not be permanently damaged by the

entry of water. If water leaves a plant cell by osmosis the cytoplasm

will shrink, but the cellulose cell wall will continue to give some
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