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What are the factors affecting osmosis?

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Introduction

AT1 Experimental Investigation What are the factors affecting osmosis? Background Knowledge 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. Semi-Permeable membrane allows small molecules to pass through, but prevents large molecules from passing through. In this diagram, the left side of the membrane has a higher concentration of glucose. The concentration wants to be the same on both sides of the membrane. For this to happen, the water on the right side, in the lower concentration moves to the left, making the concentration higher on the right and lower on the left, until they become equal. Consequently, there would be more liquid on the left side than on the right, and is shown on the diagram. When this happens in plant cells, water continues to enter the cell vacuole until the turga pressure of the water in the cell equals the cell wall pressure. Osmosis then stops, even if the concentration is still different. The cell is then Turgid. Because the plant cells take in water through osmosis, the mass of the plant increases, as does the length and width of the plant. ...read more.

Middle

Apparatus list * Scalpel * Top Pan balance * Beakers * Stop-watch * 10mm Cork Borer * Glucose solutions at 0.2M, 0.4M, 0.6M & 0.8M * Pure water * ruler Diagram Results chart Concentration Original Mass (g) Final Mass (g) Change in Mass Average change Distilled water 1.61 1.68 1.74 1.82 +0.13 +0.14 +0.135 0.2M 1.74 1.72 1.64 1.76 -0.10 +0.04 -0.03 0.4M 1.69 1.72 1.69 1.71 0 -0.01 -0.01 0.6M 1.71 1.74 1.69 1.71 -0.02 -0.03 -0.025 0.8M 1.74 1.70 1.63 1.60 -0.11 -0.10 -0.105 Analysis The question that I asked at the beginning of the investigation was; "what are the factors affecting osmosis?" I have investigated the effect of the concentration of glucose on osmosis, using the change in mass to measure the effect. My results show that the plant at first gained mass as it took in water, with the potato in the distilled water taking on the most, and the 0.2M taking on less, but still an notable amount. The plant then lost mass, as it lost water, with the potato in the 0.4 and 0.6M concentrations losing just a little, but the 0.8M losing more. ...read more.

Conclusion

Since we measured to 2 decimal places for the mass and used sharp enough scalpels to measure the length to 0.5mm, the accuracy should be very good, and I think our results reflect this. The only thing that may be slightly inaccurate was the timing using stopwatches, because this depended on us stopping them at the right time, and removing the potato promptly, which could be somewhat imprecise. However, osmosis is a fairly slow process, so this should not have impacted on our results in any obvious way. If I were to repeat the investigation, one improvement I could make would be to increase the volume of liquid I used to submerge the potato in. This means that the potato would be completely covered, so that concentration would not change as it would if the potato was partly in the air. Also, leaving the potato in the liquid longer would give us more apparent results, with bigger differences in mass and length, as the osmosis would have longer to work. Extensions could include looking at other plants, to compare the glucose concentration of the cells. However, perhaps one that would extend our particular investigation more specifically would be to do more experiments using more concentrations between about 0.35M and 0.5M to try to pinpoint the exact concentration of the potato cells. ...read more.

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