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An Investigation to Determine the Water Potential of a Plant Tissue.

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Introduction

An Investigation to Determine the Water Potential of a Plant Tissue An Investigation to Determine the Water Potential of Plant Tissue Introduction The plant tissue to be used in this investigation will be that of potato tubers. The cells of a white potato are parenchyma cells. These cells are large, thin-walled, and usually have a large central vacuole. They are often partially separated from each other. In areas not exposed to light, as in a potato, food storage in the form of starch grains is the main function (Where light is present, e.g. in a leaf, photosynthesis is the main function). The amount of water present in these cells results in them having certain water potentials. Water potential is the amount of water available to move across a membrane from a solution. The process by which water moves across a membrane is known as osmosis and is described as the diffusion of water through a selectively permeable membrane from a region of high water potential to a region of low water potential. It therefore moves down a water potential gradient. Any solution with high concentration will have a low water potential and visa versa. The highest water potential being that of water with a value of 0. Solutes in water give the solution negative water potential. The direction in which the water moves, in or out of the cell will depend on the relative water potential inside the cells (the cytoplasm) and in the surrounding solution (sucrose solution). If the net movement of water were into the cell it would become turgid, the cytoplasm and vacuole pushed up against the cell wall, making the cell stiffer and wider. ...read more.

Middle

Great care must be taken when using the cork borer and scalpel to avoid injury. It may also be advisable to wear a lab coat to protect clothing from any solutions. References Cambridge Advanced Sciences Biology 1 Investigating Osmosis Osmosis is the movement of water molecules across a partially permeable membrane from a region of high water concentration to a region of low water concentration. It can be affected by several different variables including concentration of sugars. In this investigation I will be exploring the effect of varying concentration of sucrose sugar solution on the amount of osmotic activity between the solution and the potato chip of a given size. Osmosis is basically a special kind of diffusion involving water molecules, which occurs when two solutions are separated by a partially permeable membrane. The water diffuses from the weaker solution to the stronger solution. Tiny holes in the membrane allow small water molecules to pass through, but the glucose molecules are too large to pass through the semi- permeable membrane. Plant cells have a cell wall surrounding them, this is very strong. When they take in water by osmosis they begin to swell, but the cell wall stops them bursting. Plant cells become swollen and hard when they are put in dilute solutions. The pressure inside the cell will rise and eventually is so high no more water can enter the cell. This works against osmosis. But being like this is very important to plants, as it is what makes the green parts of them stand up in the sunlight. When plant cells are placed in concentrated sugar solutions they lose water by osmosis and they become weak and thin, because the sugar is more concentrated outside the plant than in the plant itself. ...read more.

Conclusion

Even though this was a pattern the decrease was not particularly large at any certain time. In my opinion this experiment was very successful. I managed to obtain a large quality of accurate results from which I was able to produce an informative graph. I think I took the right amount of results but taking more would of made it more accurate. The 1day time period was enough time to allow osmosis to occur but I could of easily gained similar results in a shorter time span. If I were to repeat the experiment I would try and find out the saturation point of the potato pieces. I had an adequate but creating more concentrations is a possibility if I was to repeat this experiment as I could produce a wider range of results. I found preparing the sugar solution the most difficult part of my experiment because I could never be 100% sure I was using accurate amounts. A more accurate pipette would have been useful. In future I could have used a burette, which would have ensured that the amount of solution in the tube was more accurate. I could of also weighed each potato piece to a more accurate scale i.e to three of four decimal places. My results were fine even though the exact results were not persistent for both attempts at the experiment. This cause was properly human, I may not have dried some potato pieces as well as other, and some would then have more excess water adding to the mass. If I repeat the experiment again I will look into finding some other way of drying the potatoes more thoroughly. However I think the experiment was very successful and I am pleased with the complete comparison of my results with the initial prediction I made. ...read more.

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