Potato chips and Osmosis

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Khalid Edah-Tally                Biology Coursework 2005

Biology Coursework

Potato chips and Osmosis

What it’s all about…:

                        I am going to conduct an investigation to find out at which sugar concentration osmosis best takes place on a potato chip.

Osmosis is defined as the net movement of water or any other solution with molecules from a region in which they are highly concentrated to a region in which they are less concentrated. This movement must take place across a partially permeable membrane such as a cell wall, which lets smaller molecules such as water through but does not allow bigger molecules to pass through. The molecules will continue to diffuse until the area in which the molecules are found reaches a state of equilibrium, meaning that the molecules are randomly distributed throughout an object, with no area having a higher or lower concentration than any other.

        

Membranes are very thin sheets of material which surround living cells. For example, thin cellophane is a membrane. They have tiny holes in them to allow small particles to get through. Particles like water molecules can get through easily; however, larger molecules such as starch cannot. If a membrane separates a strong and a week solution, the water molecules will pass through the membrane until each solution is of equal strength.

Some Information on Plant Cells:

Plant cells always have a strong cell wall surrounding them. When they take up water by osmosis they start to swell, but the cell wall prevents them from bursting. Plant cells become "turgid" when they are put in dilute solutions. Turgid means swollen and hard. The pressure inside the cell rises and eventually the internal pressure of the cell is so high that no more water can enter the cell. This liquid or hydrostatic pressure works against osmosis. Turgidity is very important to plants because this is what make the green parts of the plant "stand up" into the sunlight.

When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become "flaccid." This is the exact opposite of "turgid". The contents of the potato cells shrink and pull away from the cell wall. These cells are said to be plasmolysed.

When plant cells are placed in a solution which has exactly the same osmotic strength as the cells they are in a state between turgidity and flaccidity. We call this incipient plasmolysis. "Incipient" means "about to be".

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Aim:

                        My aim is to investigate the effect of varying concentrations of a certain sugar solution on the amount of osmotic activity between the solution and a potato chip of a given mass.

Variables:

                        Variables are the things that we are going to change during the investigation, and are things which will affect the experiment on the whole. One of the variables will be the concentration of sugar in the solution. This will have a big impact on the experiment as different concentrations of sucrose will affect the potato chips in different ways. For the purpose of my ...

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