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How varying one factor effects the rate of osmosis between potato cylinders and Sucrose solution

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Introduction

Biology Coursework PLAN Introduction I am doing an investigation, to find out on how varying one factor effects the rate of osmosis between potato cylinders and Sucrose solution. Osmosis is the diffusion of solvent (usually water) particles through a selectively permeable membrane from a region of high solvent concentration to a region of lower solvent concentration. Examples of Selectively permeable membranes are (a) the cell membrane, and (b) visking (dialysis) tubing. Such membranes are thought to have tiny pores that allow the rapid passage of small water particles, but restrict the passage of larger solute particles. Since the membrane is Selectively permeable, Osmosis is important in the passage of water into and out of cells and organisms, and depends on Osmotic pressure. Osmotic pressure The pressure exerted by the osmotic movement of water that can be demonstrated in an Osmometer. Water moves into the solution in the visking bag by Osmosis, causing the liquid level in the tube to rise. Osmotic pressure depends on the relative solute concentrations of the solution s involved. The Osmotic pressure that a solution is capable of developing is called its osmotic potential, but is only realised in an Osmometer. Cell membranes All living things have certain requirements they must satisfy in order to remain alive. These include exchanging gases (usually CO2 and O2), taking in water, minerals, and food, and eliminating wastes. These tasks ultimately occur at the cellular level, and require that molecules move through the membrane that surrounds the cell. ...read more.

Middle

This will keep the water potential in each potato cylinder equal, for the experiment on the next day. 4. Next day. Measure out and cut the required lengths and widths of potato cylinders needed, using a vernier calliper. 5. Measure out and add 30cm� of sucrose solution to each of the cups. 6. Blot dry, then weigh the potato cylinder that is to be used in the experiment and note it down in the table. 7. Now place it into the cup of Sucrose solution for its allotted amount of time (30mins). I have made the time 30 minutes because, if the cylinders were left in the water for too long, the concentration of the solution would change. Meaning that the results would be unfair, as the experiment would have been carried out in a changing environment (as the environment was meant to be kept constant). 8. Blot dry, and weigh the potato cylinder again, and note down the weight in the table. 9. Clean and rinse the apparatus with distilled water, and do the same thing as above except with the different sized potato cylinders. The potato cylinder will be cut up in the following way: The results from the experiment will be recorded in the form of a table, which will look like as follows: Volume of Sucrose solution (cm�) Surface area of potato cylinder (mm�) Initial mass (grams) Final mass (grams) Percentage change in mass Average percent change Rate (Percentage change in mass / 10 mins) ...read more.

Conclusion

This is because I need a good range of results to obtain accurate and reliable results. There will be 10 points, which means that 6 different surface areas will be used to obtain these results. The surface areas will not be too close to each other, as I need a wide spread and a good range of results. If the surface areas I used in my experiment were very similar to each other, my graph will have a clump of results in the middle of the graph. This will lead to not drawing a good line of best fit, and will not illustrate what happens to the rate of osmosis as the surface area increases etc. Therefore 10 wider surface areas will give me points that are slightly more further apart and allow me to draw a better line on my graph, which will enable me to show what happens as the surface area and rate of osmosis increase. The surface areas that I will use in my experiment will be: 1. 17.3cm� 2. 18.8cm� 3. 19.8cm� 4. 22.0cm� 5. 23.6cm� 6. 27.3cm� 7. 28.8cm � 8. 29.8cm� 9. 32.0cm� 10. 37.3cm� As you can see, I have a wide range as the surface area ranges from 17.3cm� to 37.3cm�. Therefore, the surface area is over double from what it started out as. This wide range will give me points on the graph that aren't cramped together, but nicely spread out so that I can draw a line of best fit. Secondary sources - Key Science Biology by David Applin (pages 143-144) - GCSE Biology revision guide by 'The Science Co-ordination group' (page 5) - Microsoft Encarta ...read more.

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