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To investigate the process of osmosis and discover the water potential of a potato or the concentration of sucrose in a potato cell.

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Introduction

Aim To investigate the process of osmosis and discover the water potential of a potato or the concentration of sucrose in a potato cell. Hypothesis Osmosis is the process of water travelling through a partially permeable gradient from areas of high concentration of water to areas of low concentration. This is known as following the 'concentration gradient'. Osmosis occurs in cells, through cell membranes. The amount of water that will move through the cell membrane of the potato and the direction of the movement depends on the concentration of solution the potato is placed in. If the potato is placed in a solution with a higher concentration of water than that of the potato, water will pass through the membrane into the potato. Hence the weight of the potato will increase. If the concentration of the solution is lower than that of the potato, water will pass out of the potato and the weight will decrease. A graph can be drawn to show this principle... However, it is more difficult to measure the concentration of water in a solution than it is to measure the concentration of sucrose, so this graph will be the one I will create using the results from my experiment. ...read more.

Middle

Results This is the table of raw data obtained during the experiment. Mass (g) Concentration (mol/dcm3) 0 mins Av. 15 mins Av. 30 mins Av. 45 mins Av. 0.0 0.78 0.79 0.75 0.77 0.77 0.77 0.74 0.76 0.83 0.86 0.81 0.83 0.83 0.87 0.83 0.84 0.2 0.87 0.88 0.93 0.89 0.88 0.88 0.94 0.90 0.77 0.76 0.81 0.78 0.92 0.91 1.00 0.94 0.4 0.64 0.71 0.83 0.73 0.59 0.66 0.80 0.68 0.58 0.62 0.80 0.67 0.60 0.66 0.81 0.69 0.6 0.70 0.69 0.73 0.71 0.66 0.65 0.69 0.67 0.59 0.59 0.62 0.60 0.61 0.60 0.64 0.62 0.8 0.72 0.73 0.72 0.72 0.68 0.70 0.68 0.69 0.61 0.66 0.62 0.63 0.57 0.65 0.56 0.59 1.0 0.64 0.67 0.73 0.68 0.61 0.66 0.71 0.66 0.52 0.58 0.58 0.56 0.49 0.53 0.56 0.53 These graphs represent the change in mass in the pieces of potato throughout the experiment. Each line represents one piece of potato. This table shows the percentage gain or loss of mass of the potato in each solution. Concentration of Solution (mol/dcm3) Increase of Potato 1 Increase of Potato 2 Increase of Potato 3 Average Percentage Increase 0 6.41% 10.13% 10.67% 9.07% 0.2 5.75% 3.41% 7.53% 5.56% 0.4 -6.25% -7.04% -2.41% -5.23% 0.6 -12.86% -13.04% -12.33% -12.74% 0.8 -20.83% -10.96% -22.22% -18.00% 1 -23.44% -20.90% -23.29% -22.54% This is a graph of concentration against average percentage increase. ...read more.

Conclusion

The graph I believe would have been a straight line if I had measured the weight of the potatoes to 'constant mass'. This means I should have continued replacing the potatoes back into the solution until they become fully turgid and the mass no longer changed. The method could have been improved by measuring to 'constant mass' and also by measuring the percentage change of mass in more concentrations, e.g.) 10 instead of 5. This would have let me plot more points on my graph and I would have been able to state my conclusions with more certainty. There were many places where errors could have happened in this experiment. The potato discs could have been different shapes and therefore had different surface areas, the solutions may not have been completely accurate, not all of the excess solution may have been removed before each weighing and the time between weighings could have varied. It would have been very difficult to regulate these factors exactly, a machine could have been used to cut the potatoes to size but this would have been needlessly expensive. If more time was available, the weighing of each potato could have been done separately so there wasn't so much of a hurry every time the stop-clock said it was time to weigh. Biology Osmosis Practical Page 1 Andrew MacKay 11S ...read more.

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