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Results Table -The presence of starch and glucose.

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Results Table -The presence of starch and glucose (Part B) Below is a table of my results. It shows what the colour change was for each test we did (one for the presence of starch and one for glucose). The changes in colour indicate whether or not starch or glucose is present. Test Done Potato Swede Iodine Test (Original colour red/brown) Colour changed from red/brown to blue/black Slight colour change from red/brown to dark brown Is there a lot of starch present? Yes - a lot of starch is present. No - However, there is some evidence of starch being present. Benedict's test (Original colour blue) Colour changed to green Colour changed to orange/brick red Is there a lot of reducing sugars present? No - However, there is some evidence of glucose being there Yes - a lot of glucose is present. A-Level Biology: Assessed Practical Aim to investigate water relations in two plant tissues ANALYSIS There are four basic ways in which molecules can move from one area to another. They are: * Diffusion * Osmosis * Active Transport * Bulk Transport In this experiment we are looking at osmosis. To be able to analyse and explain this experiment, we have to know what osmosis is. Osmosis is the movement of molecules from an area of higher water potential, to an area of lower water potential through a partially permeable membrane. ...read more.


The more solute a solution is, the more negative the water potential is. Pure water has a water potential of zero. Once a solute is added, for example sugar, the more negative the solution becomes. Swede has more solutes than potato and so has a more negative water potential, as my results showed. EVALUATION In this experiment, there are several sources of error that have shown up on the graph. Theses are known as anomalies. Anomalies are points on a graph that do not follow the line of best fit. These could be caused by a difference in room temperature, human error, potato and swede not all being the same size, and many others. We try and keep errors to a minimum, by keeping variables the same apart from the one we are testing. If we can manage to keep variables the same, then there will not be as much error in the experiment. Any anomalies on my graph, have been highlighted and below are some possible causes of error. The main problem of the experiment was the cutting of the tissues. This caused the most difficulty because of the precise measurements were required. We were required to cut the tissues at 0.5 cm by 0.5 cm by 7.0 cm. The equipment we were given did not cut either the potato or swede easily. This led to a huge inaccuracy between my vegetables. It is so important to have both potato and swede to have the same dimensions. ...read more.


However, I cannot be absolutely sure of this statement. This is because this figure came from a graph that was a line of best fit. Therefore, it is based on interpretation of where the line crosses the x-axis. I can be sure that potato's water potential is closer to zero than swede. Swede is more negative than potato because swede has more solutes than potato and therefore it is more concentrated. To prove my line of best fit is correct, I could test the tissues at more precise concentration. For example, I could test potato in every concentration between 0.2 and 0.4 moles because I believe it is between these two points that equilibrium is reached. So, I would test potato in solutions of these moles 0.24, 0.28, 0.32, 0.36, and so on. Another experiment that could be done is comparing two vegetables that are closer in relationship. Potato and swede are like two opposite (one has a lot of starch the other does not). Using two vegetables in the same family, for example, normal potato and sweet potato. In conclusion, despite any anomalies that occurred, my results are still valid and reliable. However, they can be improved by having even more control over the variables that you do not wish to change. This experiment is open to a lot of other further deeper experiments. These other experiments can help validate any explanation given or put forward. They can also make my data more reliable. Ms. Khadjeh Stephanie Jones SF02 01/12/2002 ...read more.

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