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# Osmosis is a special type of diffusion involving only water molecules.

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Introduction

Shane Sinclair Biology Biology Coursework Plan Background Knowledge Osmosis is a special type of diffusion involving only water molecules. The definition of osmosis is the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. If a plant cell is surrounded by a solution of water that has a higher water potential than that of inside the cell, the water will enter the cell and push the contents of the cell against the cell wall. If the plant cell was surrounded by lower water potential the water will pass out of the cell. This will make the protplast pull away from the cell wall and shrink. The cell has been plasmolysed.(class notes-osmosis and water potential). I have done a preliminary experiment called "The change in mass of a potato after being in different types of water potential." In this experiment a piece of potato was placed in sucrose solutions of different water potentials and weighed, this weight would be compared to the weight of the potato before being placed in the solution and the difference would be plotted on a graph. ...read more.

Middle

Once the 24 hours is up I shall take the pieces of sweet potato out of the sucrose solution and weigh them on the electronic balance. After that I will calculate the weight loss of each piece of sweet potato. The experiment will be carried out three times to ensure that there was no mistakes made. A mean result will be take from these results, then the standard deviation will be worked out. Controls and Variables The factors that I shall keep the same during this experiment will be the size of the pieces of sweet potato, the amount of sucrose solution and the time in which the experiment will take. The only variable in this experiment will be the different types of solution i.e. 0.4, 0.5, 0.6, 0.7, 0.8 and 1.0. Safety During the carrying out of this experiment I shall have to take some safety precautions. One of these safety precautions will be to ensure that the electronic balance is kept well away from any wet substances and when weighing the sweet potato the potato must be dry. Another precaution that should be taken is in the cutting of the pieces of sweet potato. ...read more.

Conclusion

Each potato should have the exact same surface area allowing the experiment to be fairer so that there would be the same area for the water to diffuse across. The amount of sucrose solution could have also caused the experiment to have slight problems. The transfer of the solutions from the measuring cylinders to the test tubes may cause some of the solution not be have transferred as some droplets may be left in the measuring cylinder. Another possible factor that could have being changed is the recording of temperature. Temperature should have been kept constant because an increase in temperature will make the water diffuse faster. Although a few things in the carrying out of my experiment could have been changed I would still have came to the same outcome. I found that my results were fairly accurate as they all had a standard deviation of around 2 which shows that although my results weren't perfectly accurate they were all of around the same standard deviation. I didn't have many anomaly results as all of my results were around the same region. There were some differences in results, which could have been caused by the inaccuracy of my drying of the potato before weighing or the possibility of a difference in amount of sucrose solution due to the inaccuracy of my measuring. ...read more.

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