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Year 10 coursework – smosis How does the concentration of salt solution affect osmosis in potatoes? Introduction Osmosis is movement of water through a selectively permeable membrane, from where there is a higher water concentration (or water potential) to where the water concentration is lower. In this piece of coursework I will answer the question, ‘How does the concentration of salt solution affect osmosis in potatoes?’. If you put a piece of potato into pure water, the water concentration is obviously higher outside the potato. Therefore water moves into the potato by osmosis. This will cause the potato piece to swell. However, if you put a piece of potato into a strong salt solution (where the water concentration is low), then water will move out of the potato. The potato piece will therefore shrink. If a salt solution has exactly the same water concentration as the potato piece, then it is likely that there will be no overall movement of water in or out of the potato. Therefore, the potato piece will stay the same size. Salt is a solute, when it is concentrated inside or outside the cell, it will draw the water in its direction. This is also why you get thirsty after eating something salty. A cell can only become flaccid by losing water. The chain of events starts with water leaving the cell through the cell membrane by osmosis because the water concentration outside is lower than that in the cell. As water is lost the vacuole gets smaller as it is used to top the cytoplasm up. This reduces the volume of the cell contents so the membrane begins to shrink away from the cell wall. At first it will stay in contact with the wall at several points, but pretty soon it will shrink away from the wall completely. If the process continues the vacuole will disappear completely and the cytoplasm will continue to shrink. Since the contents are no longer pushing outwards against the wall the cell is no longer firm. Many cell membranes behave as semi permeable membranes, and osmosis is a vital procedure in the transport of fluids in living organisms, for example, in the transport of water from the soil to the roots in plants. If a cell is in contact with a solution of lower water concentration than its own contents, then water leaves the cell by osmosis, through the cell membrane. Water is lost first from the cytoplasm, then the vacuole. The living contents of the cell contracts and eventually pulls away from the cell wall and shrinks, this is known as Plasmolysis. If you put a plant cell in water, water enters by Osmosis, then swells up. However, the cell will not burst. This is due to the fact that the cell walls are made from cellulose, which is extremely strong. Eventually, the cell stops swelling, and when this point is reached, we say the ce ll is turgid. This is important, because it makes plant stems strong and upright. The experiment I will do is to find the water potential of a potato, by putting potato pieces into different solutions of salt of known concentrations, until I find the concentration where the potato piece stays the same size. To make this experiment a fair test, I would need to keep everything else constant as far as possible. For example, I need potato pieces of the same size, and should always use the same volumes of salt solutions. Prediction I predict, that as concentration increases, the weight and length of the potato chip will decrease. My reasoning behind this, is that the higher the concentration of the salt solution, the lower the concentration of water. When the potato chip is put into the solution, it will, by osmosis lose some of its water, and the water will diffuse into the solution of salt, causing the potato chip to lose water, thus decreasing in weight and length. However, if a potato chip is placed into a solution of 0 molar concentration, it should gain weight, width and length. This is because the solution has more water potential (its molecules’ ability to move) than the potato chip, and so water moves from a region of high concentration (the solution) to a region of low concentration (the potato chip.) Conclusion To conclude this piece of coursework, I can say that the movement of water through a selectively permeable membrane is affected by concentration of salt solution, or by any other solution. The higher the concentration of salt solution, the more the potato chip will lose its weight, width and length. Because water molecules have kinetic energy, they are constantly moving around in gaseous or liquid form, moving randomly from one place or another. The greater the concentration of water molecules in a system or solution, the greater the total kinetic energy, and the higher its water potential. This means, that as the concentration of salt increases in a solution, the concentration of water decreases, lessening the solution’s water potential, and lessening its ability to move between solutions by osmosis. Relating this to the potato chips: basically, as the concentration of salt in each solution increases, the water in that solution is less able to move to the potato, causing water from the potato to move to the solution, decreasing its length, weight and width. Osmosis is established when a semi-permeable membrane is placed beween two solutions. In biological systems osmosis is the exchange of water between the toplasm and the surrounding medium, with the plasm membrane being the semi- permeable membrane. An example of this in my results is the test at 1 molar. In other words, it becomes dehydrated and loses water through plasmolysis. If the concentration of the salt solution (in our case Glucose solution) outside the cell is less than that inside the cell, this means that the solution is Hypotonic to the cells of the potato chip. The water will diffuse into the cells, making it turgid. This would explain why potato chips put into a solution of 0 molar seemed very firm compared to the potato chip used for 1 molar, this was because the cells of the potato had lost their turgor, and had become flaccid.