The effect of osmosis on weighed potato chips

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Osmosis Coursework

Introduction

In this piece of coursework, I will be looking at the effect of osmosis on weighed potato chips.  I will be using different concentrations of a salt solution to show this.

Scientific Knowledge

Osmosis is the movement of water particles through a semi-permeable membrane from a high water concentration to a lower water concentration (so basically it is a special type of diffusion involving water molecules).  A semi-permeable membrane is a membrane with microscopic holes in it.  These holes are very small which only allow small molecules, such as H2O, through.  A good example of a semi-permeable membrane is visking tubing.

The water molecules actually pass through both sides of the membrane in a two way flow motion but as there is a higher concentration on one side and a lower on the other, you will find that there will be a steady net flow from the higher concentration of water to the lower.  This will take sometime to show a significant effect.  This then causes the higher concentration of solutes region to fill with water particles.  The water particles act as if they are trying to dilute it so as to even up the dispersion of solute.

This process of osmosis makes some cells swell up and become turgid.  With plant cells this is a great property as this helps the support of the green plant tissue.

There are two different cells, which are animal cells and plant cells.  An animal cell looks like this:

As you can see, the water molecules would have to pass through the cell membrane to get into the cell and this diagram gives a fully labelled picture of the plant cell.  Bellow is the animal cell:

As you can see from this diagram, the animal and plant cell both have a cell membrane but the animal cell is different to the plant cell in other ways, which are all listed below:

This means that the animal cell won’t be able to hold many small water molecules as the molecules go into the cell membrane of the animal cell and as you can see from the diagram, the cell membrane will not be able to hold too many molecules as it will burst otherwise.  The plant cell can hold a lot more small water molecules, as upon osmosis, the molecules would go into the cell wall instead of the membrane, which can hold a lot more molecules, and so therefore will not burst if too many molecules are in the cell wall.  Therefore that is why I am using plant cells (in this case, a potato) in this experiment.

Osmosis looks like this (see next page):

As you can see from this diagram, the small water molecules would pass from the weak solution into the strong solution by using osmosis.  The two solutions are separated by a semi-permeable membrane, which allows small water molecules through it but not larger molecules because the semi-permeable membrane has tiny microscopic holes in it to allow only the water molecules, which are small enough to fit through the semi-permeable membrane.

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Turgor pressure is the amount of water that is allowed into a cell.  When plants have enough water their cells can absorb it and therefore the contents of the cell begin to push against the cell wall.  This gives support to the plant.  The cell once full of water is called turgid.

        The turgor pressure supports the leaves in a plant.  However, when the turgor pressure drops within the plant cells, the leaves then drop as there is less support.  When a cell looses its turgor pressure it becomes a flaccid cell.

        A flaccid cell allows a lot of ...

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