An Investigation to find out how different strengths of salt solution affect potato cells through osmosis.

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Biology Coursework 2003

An Investigation to find out how different strengths of salt solution affect potato cells through osmosis.

Aim

I aim to investigate the effect of different concentrations of salt solution on potato cells when osmosis occurs.

Introduction

I intent to set up this experiment using equally sized cylinders of potato submerged in salt solutions of different concentrations. I will then observe the percentage change in mass over a set period of time. This will show me how much osmosis has occurred.

Scientific Theory of Osmosis

Osmosis is defined as the solvent of any solution being able to pass through any semi-permeable membrane from a region of high concentration to a region of low concentration until both solutions reach a state of equilibrium. This means that water can flow through a porous material, such as a cell wall or visking tubing, in order to balance the levels of concentration. The molecules are then randomly distributed throughout the solution.

Water particles are small and can therefore easily fit through the material; however, larger particles such as salt or glucose are too big to fit through the material.

        Osmosis has a significant effect on living cells. Animals cells will burst in pure water because, as the cytoplasm is fairly concentrated, the water, which is less concentrated, will enter the cell. As the dissolved substances in the cytoplasm are larger, they cannot escape so the cell becomes swollen and may burst.

        If an animal cell is placed into a more concentrated solution, the water in the cell will flow out into the more concentrated solution in order to dilute it. This will cause the cell to shrink.

        Plants cells however are very different as they have a cell wall which is very strong and fully permeable; however plant cells also have a cell membrane which is only partially permeable.

        If a plant cell is placed in pure water, it will not burst because of its strong cell wall. The cell will still take water in by osmosis, as in the animal cell. The cytoplasm will press against the cell wall but it will not burst. A cell like this is said to be turgid. This means it is firm and tight and will help a plant with no wood to stay upright and keeps its shape. Plant cells are usually turgid.

        Plant cells in a concentrated solution behave very differently. Like the animal cell, water flows out by osmosis and the cytoplasm and vacuole will shrink. The cytoplasm stops pushing against the cell wall and the cell becomes floppy or flaccid. This is what causes plants to wilt. If the solution is very concentrated, lots of water will diffuse out causing the cytoplasm to shrink further. Because the cell wall cannot shrink, the membrane tears away and the cell become plasmolysed. This is quite rare and usually kills the cell.

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        When plant cells are placed in a solution which is exactly the same concentration as the cytoplasm, they are between turgidity and flaccidity. This is called incipient plasmolysis. “Incipient” means “starting to happen”.

 

Prediction

I predict that the more concentrated the solution is, the more the mass of the potato cylinders will decrease. I think this because osmosis occurs when the concentration of the solution surrounding the cell is different to the concentration of the cytoplasm. If the solution in the beaker is more concentrated, water from inside the cell will diffuse out of the potato in order to ...

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