RELIABILITY/ FAIR TEST
I must control many variables in this test. I will control the time that they are left in the solution, as this will greatly affect results if they are left in for different amounts of time. Also I must control how much I dry the chips before weighing them, because if I leave some excess water on one of them, it will be an unfair test, as ill be weighing the water as well as the chip. Another point is simple, but just to make sure that the scales I am weighing the chip on are at 0 before weighing the chip, as it may add some mass to the chip. I will use 5 different solutions, starting at 0 molar and going up in 0.5 molar concentrations. I have chosen this because they are equidistant, allowing for easy graph drawing, and also because from the preliminary experiment, I know that this will give me results that can show me the concentration of sucrose in the cells sap, and also go on to show me the concentration that the cell will plasmolyise at. I will also control the variety of potato- I will only use 1 brand, as different brands and types may have different concentrations of sucrose in their cells. . Also all solutions will be measured in beakers to 20 cm3, as if there was a higher volume in one solution, it would take longer to fully even out. My results will be quite reliable if I control the points above, and any anomalies will be identified.
SAFETY
There are no points concerning safety, as it involves only sucrose solutions. However I must take care not to drop wet test tubes.
EQUIPMENT
We will use the following equipment in our experiment:
- 3 same branded potatoes
- Scales accurate to 2d.p
- 4mm diameter corer
- 3 test tube racks
- 15 test tubes
- Distilled Water
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Measuring beakers with maximum of 10cm3 intervals.
- 1molar and 2 molar sugar solutions (also used to mix the 0.5 molar and 1.5 molar solutions.)
- 2 Pipettes
- And some paper towel
Preliminary study
I carried out a preliminary experiment to decide on all of the above specifications. I tried using 3 chips in each solution, and I used 3 different solutions. I left them in there for 15 minutes, which provided us with odd results that are show below. As you can see, the results graph is completely wrong. It suggests that the concentration of sucrose in the less sap is less than water, which is stupid, as all potatoes contain some sucrose, as if it didn’t, it wouldn’t have grown. These results cannot tell me much, as they do not follow what you would expect.
Prediction
My prediction above is in a slight ‘s’ curve, which is based on the test A of my preliminary. Test A seemed to be the most logical to choose as it followed the patterns that I would expect it to. As we can see from it, the water solution increases its weight, and it shows that the cells concentration is , as this is where it crosses the x-axis. And also it shows us that the cell is fully plasmoliesed at around . this is because the graph starts to level off and that means that the chip is not losing any more weight, because the cell is fully plasmolyised.
BY MICHAEL PEARCE
