Osmosis is the diffusion of a solvent from a less concentrated solution into a more concentrated solution through a semi-permeable membrane, permeable to the solvent but not to the solute.

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Christian MacNamara 11MC                                                

BIOLOGY - Science Investigation:

Osmosis

PLANNING:

        Scientific Knowledge

        Osmosis is the diffusion of a solvent from a less concentrated solution into a more concentrated solution through a semi-permeable membrane, permeable to the solvent but not to the solute. (The Oxford Popular English Dictionary, reprinted 2000, Oxford University Press.)        Diffusion is the movement of particles from a high concentration to a low concentration until they are spread out evenly. (Biology Exercise Book 1, 14/09/01.)

        Diffusion consists of the movement of large and small molecules, and in the case of Osmosis, the small particles are water (H2O) and the large particles are sugar (sucrose).

        The processes of Osmosis and Diffusion will be occurring in this experiment when the water in the potato diffuses from the area of high concentration (the potato) to the area of low concentration (the solution).

        Water (H20): Water is chemically formulated from 2 parts Hydrogen (H2) and 1 part Oxygen (O)

        

        Sucrose (C12H22O11): is a sweet crystalline dextrorotatory disaccharide sugar that occurs naturally in most plants and is obtained commercially especially from sugarcane or sugar beets (Encyclopaedia Britannica online dictionary.) Sucrose is used in the solution for this experiment.

        Plasmolysis: is the shrinking of the cytoplasm away from the wall of a living cell due to outward osmotic flow of water (Encyclopaedia Britannica online dictionary.) The process of Plasmolysis will occur when the water diffuses from the potato to the sucrose solution due to Osmosis.

Factors/Variables effecting Osmosis:

        - Temperature – will affect the speed of Osmosis

        - pH – will affect the strength of Osmosis

        - Pressure – will determine change in mass of potato

        - Concentration – will affect results of experiment

        - Amount – different amounts will produce different results

        - Cell Surface Area – will determine level of Osmosis

        - Volume of Solution – will affect the amount of Osmosis that can occur

Prediction:

        I predict that the higher the concentration of sucrose in the solution, the more water diffuse out of the potato and into the solution. We know that Osmosis is the flow of water in a solution through a membrane while the other molecules are unable to pass through the membrane. The cell membrane of the potato is semi-permeable (it lets some substances in but not all substances). This means that water particles can diffuse into the cells, via osmosis. This occurs if the cells are surrounded by a weak solution e.g. 0-4%. If the cells are surrounded by a stronger solution, e.g. 4-8%, the cells may lose more water by Osmosis. For example, if a potato cylinder was left in a solution of 6% sucrose, its mass before being 1g, then I predict that by the end of the experiment its mass will have reduced to 0.85g, a 15% change in mass. Therefore, I predict that the graph of results should look something like this:

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        Carrying out the investigation

Equipment:

        · Cutting tile – to cut the potato on so no lab surfaces are damaged

        · Knife – to cut the potato cleanly, for accurate results

· 5ml Measuring cylinder – to measure the solutions accurately, also to produce more accurate results

· Distilled water – is mixed with the sucrose to produce sucrose solution, as part of the experiment

· Sucrose – is mixed with the water to produce sucrose solution, as part of the experiment

· Potatoes – ...

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