All About Osmosis

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All About Osmosis

Introduction/What is Osmosis: Osmosis is the movement of a solvent or

liquid; usually water, through a semi-permeable membrane separating

solutions of different concentrations. The solvent passes from a less

concentrated solution to a more concentrated solution until the two

concentrations are equal. Many cell membranes behave as semi-permeable

membranes and osmosis is a vital mechanism in the transport of fluids

in living organisms; for example, the transport of water from the

roots up the stems of plants.

Osmosis is a special case of diffusion, diffusion being the movement

of particles from an area of high concentration to an area of low

concentration. Osmosis is simply the movement of water molecules from

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

concentration, across a semi-permeable membrane.

A semi-permeable membrane is a barrier with small holes in, the holes

are so small that only water can pass through them, bigger molecules

like glucose cannot. The water molecules actually pass both ways

through the membrane but because there are more on one side than the

other there is a steady flow into the region with the fewer water

molecules, i.e. into the stronger solution (of glucose). This causes

the glucose-rich region to fill up with water.

Osmosis makes plant cells swell up if they are surrounded by a weak

solution, and they become turgid, the water molecules enter the plant

cells. In a strong solution, the plant cells would shrink because the

water molecules are leaving the plant cells.

Aim: To investigate the effects of different concentrations of sugar

solutions on potato cells by measuring the change in weight of potato

tubes after placing them in the solutions for a measured amount of


What I Will Change: The concentration of sugar will be the only

controlled variable in this experiment; this will be prepared by

making a molar sugar solution and diluting it with variable quantities

of distilled water, as follows.

Concentration of Sugar solution (M)

Volume of 1M sugar solution (cm3)
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