Show the action of water moving in and out of cells (Osmosis) by using potatoes.

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Samuel Verlander                                                                                 Biology Coursework

                                                                                                                            GCSE 2004                  

Aim

To show the action of water moving in and out of cells (Osmosis) by using potatoes.

Background Science/Previous work

I have done work on Osmosis before in school on carrots, potato chips and grapes. Osmosis is the action of water from a region of high water concentration to pass through a semi-permeable membrane to a region of lower water concentration. The speed of which Osmosis takes place varies on the difference in the two concentrations.

If there is a higher concentration of water in the medium surrounding a cell, the cell will gain water by Osmosis. Although water molecules will still be able to pass across the cell in both directions, more water will enter the cell than will exit. The net result to the process is that water will enter the cell. It is likely that the cell will swell up. If there is the same concentration of water on the outside of the cell as well as the inside then water will still be passing over the membrane but the cell will stay roughly the same shape and size.

If there is a lower concentration of water in the medium surrounding the cell, the cell will lose water by Osmosis. As above, water will still pass over the membrane but it will end up with less water.

Plant and Animal cells have many differences about them and have some different consequences due to Osmosis happening.

If a plant cell is placed in a solution with a solution that causes it to keep swelling, it will get to a certain point and stop. The plant cell is now fully Turgid, with the Cytoplasm pressing against the cell wall. The cell wall prevents the cell from getting too big and bursting. Turgid means swollen and hard. Once the cell has become fully turgid, it cannot take in any more water. There is great pressure in the cell. Turgidity is an important part of most plants because the stem is made of turgid cells.

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If a plant cell is placed in a solution that causes it to lose water by Osmosis then it will become flaccid. This is the opposite of Turgid. It is when the plant cells membrane and cytoplasm shrinks away from the cell wall, which stays roughly the same shape, but is somewhat weaker, causing floppiness.

Turgid Cell                                             Flaccid Cell

Animal cells, however, can be quite different to plant cells, as they do not have ...

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