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In this experiment we are going to be studying the affects of Osmosis

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In this experiment we are going to be studying the affects of Osmosis

in Potatoes. Osmosis is the passage of water from a region of high

water concentration through a semi-permeable membrane to a region of

low water concentration.

A semi-permeable membrane is a very a very thin layer of material,

cell membranes are semi-permeable. These will allow some things to

pass through, but will prevent other things from passing through. For

example, cell membranes will allow small molecules such as Oxygen,

water, Carbon Dioxide, Ammonia, Glucose, amino acids, etc. to pass

through. But they will not allow larger molecules such as Sucrose,

Starch, and protein, etc. to pass through.

A region of high concentration of water is either a very dilute

solution of, for example, sucrose, or Pure Water. In each case there

is a lot of water: there is a high concentration of water.

A region of low concentration of water is a concentrated solution of

something, for example, sucrose. In this case there is much less

water.

When one puts an animal or plant cell into a liquid which contains

water three things can happen.

If the medium which surrounds the cell has a higher water

concentration than the cell, the cell will gain water by osmosis.

Water molecules are free to pass across the cell membrane in both

directions, but more water will enter the cell, than leave it. The

Result of this is that water enters the cell and the cell is likely to

swell up.

If the medium has exactly the same water concentration as the cell,

there is no overall movement. The cell will stay the same size. Water

will cross the cell membrane in both directions, but the amount

entering it will be the same amount leaving it, so there is no overall

movement of water. The cell will stay the same size.

If the medium has a lower concentration of water than the cell, the

cell will lose water by osmosis. The water will cross the cell

membrane in both directions, but now more water leaves the cell than

entering it. The Result of this will mean the cell will shrink.

Variables

In this experiment I am going to cut 12 potato sections, I am going to

try keeping these roughly the same size and weight. They will be

around 4cm long, and all will have an average weight of 2.74g.

The liquid that the potato sections will be put into will have

different concentrations, but they will all have a volume of 30 cm.

I am going to have 6 different test tubes which will have the same

volumes but different concentrations.
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