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Potato coursework

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Introduction

How does the concentration of a solution affect the osmosis rate of a potato Aim: The aim of my experiment is to see if the concentration of sugar solution I use will affect the rate of osmosis in potato cells. I will do this by recording data collected on the potatoes placed in different concentrations of sucrose. Research: Osmosis is a special kind of diffusion that only concerns the movement of water. If two solutions are separated by a semi-permeable membrane, which only allows certain sized molecules through there will be a net movement of the water molecules, from the less concentrated solution (the one with more water molecules), to the solution which is more concentrated (has more solute molecules). This is because as in ordinary diffusion the molecules move to even-out any difference in concentration. However, because of the semi-permeable membrane, which does not allow the larger solute molecules to cross; only the water molecules can move. The water molecules will continue to cross the semi-permeable membrane until equilibrium is reached, where the two solutions are of equal concentration. The greater the difference in the number of water molecules on either side of the membrane, the greater the water potential. Water potential is represented by the Greek letter ?. pure water has a water potential of 0kPa. As substances dissolve in the water, the water potential drops and becomes negative. ...read more.

Middle

spend in the sugar solution * Measuring cylinder - I will use a 2ml measuring cylinder so I can accurately measure different concentrations of the sugar solution * Paper towels -I will use these to dry the potatoes before they are weighed Preliminary The aim of my preliminary is to see which are the most suitable time and length to use in my main experiment. I will do the experiment as stated and use my results to come up with the suitable measurements. Results 5 minutes Length Weight before Weight after Difference 1cm 0.43 0.41 -0.02 2cm 0.81 0.78 -0.03 3cm 1.24 1.21 -0.03 4cm 1.55 1.51 -0.04 5cm 2.05 2.00 -0.05 10 minutes Length Weight before Weight after Difference 1cm 0.47 0.45 -0.02 2cm 0.86 0.82 -0.04 3cm 1.26 1.23 -0.03 4cm 1.66 1.57 -0.09 5cm 2.15 1.73 -0.42 15 minutes Length Weight before Weight after Difference 1cm 0.46 0.44 -0.02 2cm 0.92 0.87 -0.05 3cm 1.31 1.25 -0.06 4cm 1.83 1.77 -0.06 5cm 2.35 2.29 -0.06 20 minutes Length Weight before Weight after Difference 1cm 0.52 0.45 -0.07 2cm 0.84 0.81 -0.03 3cm 1.23 1.17 -0.06 4cm 1.61 1.55 -0.06 5cm 2.06 2.02 -0.04 From my results I have decided to use15 minutes to soak the potato in the sugar solution. I feel this is best as it produced consistent results and gave me enough time to set up the next experiment whilst the potato was in the solution. ...read more.

Conclusion

This could be down to any number of reasons including an inaccuracy when measuring out the solution. It could also be possible that the amount of time sI patted each potato piece to dry it could affect the end result. Although I can no be accurate when saying what affected my experiment I can guess at some of the factors that may have affected it. If I was to do the experiment again there would be a few things I would alter so I could increase the reliability of the results. Firstly I would put a lid on the test tubes. This is because water could evaporate out of the test tube causing the concentration to change. Another thing I would change is I would dry the potatoes in exactly the same way for the same amount of time for every experiment as a little bit of water left on the potato piece can affect its weight. The last thing I would change is the ruler I used. I would make sure the ruler had millimetres on it so I could make sure that each potato piece is exactly the same length. I think the results my graph produced are very reliable. They helped me come to a valid conclusion which I had predicted. To further my experiment I could vary the vegetables I use to see if the effect of concentration is the same on them. Examples of vegetables I could use are swede or parsnip, as these vegetables have similar properties to the potato. Clair Kidd-Stanton, 2107 Page 1 The George Ward School ...read more.

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