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To study what effect different concentrations of sucrose will have on potato tubers.

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Introduction

Laura Evans 105:LLB Biology Coursework: Studying the effect of the concentration of the sucrose on potato tubers. Aim: To study what effect different concentrations of sucrose will have on potato tubers. Aim: The independent variable will be the concentration of the sucrose solution. In my preliminary experiment, we used 3 different concentrations of sucrose solution, and in my experiment I shall be using 6, to get a more varied set of results. The range will be 0 Molar going up to 1M in steps of 0.2M. From my preliminary work I have also decided to use 25ml of the different solutions. The potato tubers will also all be kept at 5cm long, and will all be cut using the same corer. The dependent variables will be the length of the potato tubers and the amount of sucrose solution in each test tube. I have chosen the amount of sucrose to be 25ml because this is what worked best in my preliminary work. The potato tubers will be kept at 50mm long, because this worked best in our preliminary work. I will be using my knowledge of osmosis to identify the effects that the different concentrations of sucrose solution have on the potato tubers. Prediction: By looking at the results I got from my preliminary experiment, I predict that the more concentrated solution of sucrose will cause the greatest decrease in the size of the potato tuber. ...read more.

Middle

When plant is then submerged in a more concentrated solution, and the water molecules pass out of the cell, through the semi-permeable membrane, the cell becomes plasmolysed, where the cell membrane tears away from the cell wall and shrivels. When this happens it usually kills the plant cell because the membrane is damaged. Inside the cell, when plasmolysed, the vacuole shrinks as does the cytoplasm, which causes the cell wall to 'bend' inwards, although it doesn't shrivel because it is still quite strong. This causes the plant to wilt or droop. Diagrams from the textbook Apparatus: * 12 boiling tubes * 1 pot * 2 beakers * 2 Potatoes * Potato 'corer' * Glass rod * 2 beakers * Razor blade * Ruler * Sucrose solution * Pure water * Measuring cylinder Diagram: Method: I will be doing the experiment twice. 1. I collected all my apparatus. 2. I placed my boiling tubes in the rack and labelled them. 3. I cored 12 tubers from the two potatoes and cut them each to 4cm long, and placed each one in a boiling tube. 4. I measured out the different concentrations of solution for each boiling tube, at 25mls and then added each to their boiling tubes. 5. I waited for 2 days and then measured each tubers length and recorded my results. Risk Assessment: On a scale of 1-5 with 1 being least dangerous and 5 being most dangerous, I would rate this experiment as danger 1. ...read more.

Conclusion

Our only anomalous result was for 0.4M, where the length decreased only by an average of 0.5mm, whereas the others increased steadily between 2-4mm each time. This may have been because a slight mistake was made with the ratios of sucrose to water, or made an error with the measurements, either before putting the tuber in the solution, or after the experiment. There were some problems with the experiment, such as the temperature may not have been kept consistent throughout (night and day, temperatures differing each day) and that the concentrations were not exactly at 0m, 0.2, 0.4, 0.6, 0.8 and 1m. I also used two different potatoes for the experiment, and they would have had different concentration inside. I also measured the tubers with a ruler, which wasn't very accurate. To solve these problems, I could have kept the experiment in an environment with a consistent, controlled temperature, and measured the concentrations exact, with more accurate measuring equipment. I could also have used a single potato for the experiment, and perhaps weighed them before and after the experiment, instead of measuring them. To investigate osmosis further, I could conduct experiments that involve different quantities of solution, larger potato tubers, different plants, and experiment with different temperatures, to see if it affects osmosis. I could also use more concentrations of sucrose, such as increasing in steps of 0.05 or 0.1m instead of 0.2m. This would give a more varied set of results. I could also repeat it several times and calculate the averages. Laura Evans 105:LLB ...read more.

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