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The aim of my experiment is to find out the water potential of a potato

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Introduction

As - biology coursework. The aim of my experiment is to find out the water potential of a potato. I will do this by placing them in different molar solutions of sucrose and measuring the increase or decrease in length of the chips. I will use the osmosis theory to prove this. The theory is that if we find the isotonic solution we can state the water potential of the potato. Osmosis is the net movement of free water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane as a result of their random motion. Osmosis doesn't need energy to happen. Water potential is the direction of which water molecules move and the tendency of their direction. Pure water has water potential of 0 and all solutions have water potential smaller than 0, you cannot get water potential bigger then 0. In an isotonic solution there is no net movement of water, any movement across the semi-permeable membrane will cancel each other out. Variables Reason Temperature Chemical reactions vary in potatoes which affects the enzymes this may affect the water potential. ...read more.

Middle

4. After put them in a beaker of distilled water that is already out. 5. Next you need to calculate the amount of sugar you need for your stock sugar solution, put it in the flask and add distilled water up to the line marked on the flask. 6. Now you need to make up the different solutions of 0.M1, 0.2M, 0.3M, 0.4M, and 0.5M.Put all of the chips in and measure each chip and write which solution it is going in so you can calculate the percentage increase later. 7. Now leave them for approximately 5hours. 8. Take out the chips and measure the length and then record it. Prediction I predict that in my experiment the chip will increase in length as the water potential increases. Some chips will increase in length and some will decrease this is because of osmosis. Osmosis is when water passes through a partially permeable membrane from a region of high water potential to a region of lower water potential. Apparatus How it helps to acquire accurate and reliable data. Callipers Ensures accurate reading to two decimal places. Graduated pipette Accuracy for reading, it is much more accurate than a measuring beaker. ...read more.

Conclusion

Some chips increased in length and some decreased this is because of osmosis. Osmosis is when water passes through a partially permeable membrane from a region of higher water potential to a region of lower water potential. From my research I found that the osmotic water potential of a potato is 0.375 (www.saps.plantsci.cam.uk ). Evaluation The limitations of my method were I didn't leave the chips in for exactly the same time because I can't take them out all at the same time. Also all of the class were doing the experiment all at the same time so there was a delay when I wanted to use some of the equipment. I have quite a lot of anomalous results I think it is because I didn't measure my chips accurately before I put them in the solutions. Appendix This table shows the raw data from my experiment. Concentration of sucrose solution (M) Lengths before chips were put in the sucrose solution. (mm) Lengths after chips were put in sucrose solution (mm) Chip 1 Chip 2 Chip3 Chip 1 Chip2 Chip3 0.1 45.40 45.39 45.25 43.04 46.66 46.24 0.2 45.39 45.36 45.29 46.19 46.23 44.10 0.3 45.42 45.43 45.35 46.26 44.37 42.94 0.4 45.34 45.39 45.26 43.15 40.20 42.54 0.5 45.23 45.36 45.42 43.06 43.45 42.03 Cheryl Battlebury 1 ...read more.

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