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Investigating the Water Potential of the potato cells.

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Introduction

Shama Lalji BIOLOGY COURSEWORK Investigating the Water Potential of the potato cells. INTRODUCTION: In my experiment I will be looking at the water potential of potatoes. The potato tuber is made up of plant cells, each of which is surrounded by a cell wall that is permeable and a cell membrane that is selectively permeable. This is important as water can move in and out of this permeable membrane. The tendency of water molecules to move from one place to another is called water potential. The symbol for water potential is the Greek letter psi ?. This process is called osmosis; it can be defined as the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. Pure water has a water potential of zero, the addition of a solute lowers the water potential so all water potential values are less then zero therefore minus. Water tends to move from a less concentrated to a more concentrated solution, i.e. from areas of low negative potential to areas of high negative potential. Equilibrium is when there is the same amount of water molecules in both solutions, which therefore stops the net movement of water molecules. ...read more.

Middle

Place one potato tube into each concentration solution and then start the stopwatch. 12. Leave for 20 minutes. Stopwatch 13. After 20 minutes is up, take out the sucrose solution and remove all surface fluid from each potato tube using filter paper, making the potato have minimum contact with the hands. 14. Weigh each potato tube and make a note of the end mass. 15. Repeat twice if results are still unreliable repeat once again. RISK ASSESMENT To make the experiment safe the equipment that was sharp i.e. Scalpels and core borers were used carefully on a cutting tile. Also in case of anything getting into the eyes goggles were worn at all times. RESULTS Below there is a result table of all my results from this I have created two graphs one to show the molarity of the potato using the % change in mass and the second to show the relationship between molarity and solute potential of sucrose solution where I will be using fig 1.b for reference. Table to show results from experiment Concentration Start mass End mass Change of mass % Change of mass (Moles M) (g) (g) (g) (%) 0 (distilled water) 2.86 4.15 -1.29 +45 0.2 3.15 3.27 -0.12 +3.8 0.4 3.18 3.07 -0.11 +3.8 0.6 2.95 2.97 -0.02 +0.6 0.8 3.13 3.01 0.12 -3.8 1.0 (sucrose solution) ...read more.

Conclusion

This would also result in the solutions I used to be unreliable because if the Molarity of for example 1.0 sucrose solution was too high the potato would lose extra water making the weight loss increase causing the results to be erratic. I could have made my own solution, or use a simple titration to find out the Molarity. Out of all the errors that could have occurred from above the one I believe would have caused the greatest impact was the contamination of the solutions and unreliability of the measurements in cutting the potatoes. Increasing the number of results taken so instead of taking results from 7 different molarity levels 10 molarity levels could be taken. This would make the lines of best fit on the graphs more reliable, therefore the end results would be more reliable. Furthermore repeating the whole experiment and taking the average to make the results as reliable as possible, also ignoring any clearly anomalous results. The results I got were matching my prediction therefore they are good. My experiment was reliable but if I were to do it again to make it more reliable I would make time to repeat it and use the changes I have mentioned above. ...read more.

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