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Osmosis in potato tissue

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Introduction

PLANNING Aim: * I want to find out how the concentration of a sucrose solution affects the mass of several pieces of potato in different molarities, through the process of Osmosis. * Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration. Factors: * Temperature: This may affect the rate of osmosis as water moves quicker when warmed causing the rate of osmosis to increase. Likewise if the water is cooled the water will move slower so the rate of the movement of water will decrease. * The surface area of Potato: The rate of osmosis may be affected as the bigger the surface area, the more likely water will move through the selectively permeable membrane, as there are more holes in the membrane for it to pass through. Whereas a small surface area will less likely allow water to move through the membrane, as there are less gaps. * The total volume of the Solution: The rate of osmosis may be influenced by the total amount of solution in each boiling tube, because if you have more volume in one boiling tube compared to another it is more likely that osmosis will occur more in the greater volume than in the lesser volume. Also the inequality of the total volumes will make the test unfair, as this factor must be kept equal. * The size/length of the potato: The rate of osmosis may be affected as the bigger the size, the more likely water will move through the selectively permeable membrane, as there are more openings in the membrane for it to pass through. ...read more.

Middle

11. For each pair of potato pieces, dry the potato gently against a paper towel to remove excess water 12. Then weigh them all and record on a piece of paper there masses (grams) 13. Now place all the pairs of pieces of potatoes in the tubes that you decided to put them into. 14. Start timing for 15 minutes using the stop clock. ============================================= 15. After 15 minutes use the tweezers to gently take out each pair of potato. 16. Repeat step 11 17. Now weigh them with the electric scale and record their new weights under a new heading of mass after (grams) 18. Now work out the change in mass and the percentage change in mass Use the equation %change= original length X 100 Change in length 19. Now you have retrieved your 1st set of results. 20. If you would like to get an average then repeat steps 1 to17 but remember not to mix the content. Sample of a table: Next page preliminary work> The work on the next page allowed me to conclude that osmosis was occurring at different concentrations as the length changed. Additionally I used the preliminary work to help me know when osmosis would stop, which is after 15 minutes making the main experiment easier as there was no need to repeat the measurements every 5 minutes. Safety: * To make sure that the no accidents occur several measures have been taken 1. I will be standing during the experiment to prevent me from being harmed if any spillages occur. 2. The scalpel will be placed in a piece of cork to prevent it from harming anyone who walks by and myself. ...read more.

Conclusion

This repetition would have also allowed me to get an even more accurate percentage change in mass, as there would have been more values to observe and use. Further evidence from other experiments: * I could have investigated the change in mass again, using the same method but using the values of the concentrations which I did not use e.g. 0.1, 0.3, 0.5, 0.7 and 0.9 molar. * By looking at the graph we can estimate where no change in mass occurs and when dynamic equilibrium osmosis is taken place. But a further experiment can be carried out to find the exact point/molar at which both the concentration in the potato and the solution are the same. As the estimated value of molar is 0.35 molar, I would investigate the exact molarities of 0.26 to 0.36, going up in intervals of 0.01 molar. However it would be difficult to precisely calculate the molars as they are all to two decimal places e.g. 0.26, 0.27, 0.28.......0.35, and 0.36 molar. * We could investigate the exact same area of how molarity affects change in mass however we could use a different material to test with except from potato, and further see how different materials differ in their change in masses, after about 5 minutes. The new materials will have to be hard when raw just like potato, for example Swede, carrots, onion, garlic etc. * Lastly we could further investigate the effect of temperature on osmosis, by placing different pieces of a suitable material in different tubes filled with the constant molar of 0.0 (e.g. pure distilled water) at different temperatures. The temperatures would range from 5?C to 30?C in intervals of 5?C (e.g. 5?C, 10?C, 15?C,....25?C and 30?C) ?? ?? ?? ?? Kenneth Blake ...read more.

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