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Osmosis is the process by which different water concentrations balance out between cells. The water travels through semi permeable membranes until the concentration is equal on both sides of the membrane.

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Introduction

Biology Coursework OSMOSIS The Oxford Dictionary defines Osmosis as "the passage of a solvent through a semi-permeable partition into another solution." In Biology, Osmosis is the process by which different water concentrations balance out between cells. The water travels through semi permeable membranes until the concentration is equal on both sides of the membrane. The large particles in the highly concentrated liquid do not pass through the semi permeable membrane, but the water molecules do. Plant cells are surrounded by a cell wall made from cellulose fibres. This wall is fully permeable to allow dissolved substances to pass through it easily. There is a thin layer under the cell wall called the cell membrane, and this is only semi-permeable so only certain substances can leave and enter the cell. Any substance dissolved in water is called a solute; a solvent is a liquid that is able to dissolve another substance, called a solute, to form a solution. The water content of plant cells varies depending on environmental conditions. The water plays a vital role in the support of tissues and the transport of materials around the plant. If a plant does not have water, it may wilt, and will eventually die. Water is mainly absorbed through the roots, which are covered in specially adapted root hair cells, to create a larger surface area for absorption. It is pulled up the plant through the xylem by a pull resulting from the evaporation of water through the stomata on the leaves. ...read more.

Middle

Amount of sucrose used: This will have a very wide affect on the experiment. A strip of potato in sucrose solution will have a very different rate of osmosis than that of one in a dilute water solution. The amount of sucrose used will determine the rate of osmosis. As this is what we are going to be altering we do not need a method to keep this constant. Surface area of the potato: If one strip has a large surface area then more cells can be involved in the reaction quicker than a strip of potato with a smaller surface area. If the surface area is greater then the rate of osmosis will increase. We will use a potato borer to keep the surface area of the potato chip constant. Size of the container's opening: The rate of evaporation of the water will be dependant on the surface area of the container. If it has a large surface area then the rate of evaporation will be quicker than that of a container with a small surface area. Because of this we have decided to use 250ml beakers for all of the solutions. Plan To generate a wide variety of results, I will put the potato chippings into 5 different concentrations of sugar, 0.00 M 0.25 M 0.50 M 0.75 M, and 1.00 M sucrose solution. Using a potato chipper, chips were produced that were 7x7x50mm. ...read more.

Conclusion

Because of the low number of solutions sampled however, it would be wrong to use the graph to find out what the weight percentage change would be for other concentrations of sucrose, yet I have had to do this to approximate the isotonic solution. Evaluation Although the results of the sucrose experiments support my prediction, there is one major anomalous result, and a few smaller ones. These could be improved by altering the experiment, for example by keeping the test-tubes in a water bath at a set temperature, or by measuring the sizes of potato cylinders before and after with a more accurate method, e.g. accurate weight measurement. The test might also be more accurate if the potato cylinders were left in the solutions for a longer period of time to allow the solution to reach the core of the potato cylinders. I could have also repeated the experiment many times and found the average results, as an average would have displayed much more accurate results. Another factor is the actual specimen from which our potato cylinders were cut. We used two different potatoes, and they may have been from different plants, thus creating anomalies. If we were to repeat the experiment, we could extend the experiment to use samples from other plants, to discover whether the same would also happen in other plants, or we could use many more concentrations so we could exact our predictions for other molarities of sucrose solution, thus finding the isotonic solution a lot easier. Ciaran Sainty 10U1 Osmosis Coursework C:\My Documents\Ciaran\Coursework\Osmosis ...read more.

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