- Level: AS and A Level
- Subject: Science
- Word count: 2482
This piece of investigative work aims to prove, through two different experiments: 1. the water potential of potato tuber cells by the weighing method, and 2. the estimation of glucose in a solution using the colorimetric method.
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Introduction
AS Biology Matthew Cox cox04067214 Introduction This piece of investigative work aims to prove, through two different experiments: 1. the water potential of potato tuber cells by the weighing method, and 2. the estimation of glucose in a solution using the colorimetric method. In the first experiment, samples of potato, extracted from the same potato using a cork borer, will be weighed prior to the experiment and then weighed again at the end. The aim is to find the water potential of each sample by calculating the percentage increase or decrease in mass and therefore to find which solution is closest to the potato tuber's natural solute potential. The change can be accounted for by the amount of water taken in by each sample. In the second experiment, 10 samples will be tested in order to find how long it takes for an acidified glucose solution, coloured purple by potassium manganate (VII), to clear. The 10 samples were known amounts of glucose solutions, starting at 10% solution reducing by 1% each time. The aim of this was to plot a time-graph in order to estimate the glucose concentration of 3 unknown solutions. This estimation could be made by finding the time on the graph and seeing what glucose concentration crossed the line at that time. Determination of the water potential of root/tuber cells by the weighing method. ...read more.
Middle
Therefore, water will enter the cells through the partially permeable plasma membrane by osmosis. This explains why the greater the concentration of the sucrose solution, the more mass each sample loses, and why the closer each solution comes to pure water, the less mass it loses and in one instance, the mass it gains. As we know, water moves down the concentration gradient, not up. So if the tuber has gained mass, we can deduce that the solution has a higher water potential than the tuber. However, if the sample loses mass, we can deduce that the tuber has a greater water potential than the solution. The latter is clear for the 1.0, 0.8, 0.6 and 0.4 MOLAR concentrates and the former is true for the sample bathed in distilled water. However, I believe that the tuber bathed in the 0.2 MOLAR solution is closest to the tuber's natural potential. I say this because the start mass was 1.53gram and the end mass was 1.52grams - a loss in mass of just 0.01grams. This means that after soaking in solution for 55 minutes, hardly any molecules were exchanged across the tuber's membrane, at least not enough to change the tuber's mass by more then 0.7%. A Colorimetric Method for the Estimation of Glucose (or reducing sugars) in Solution. Glucose, a reducing agent, will reduce an acidified purple-pink solution of potassium manganate (VII) ...read more.
Conclusion
Test tube B, like the 1% solution had still not cleared when this time had elapsed and so again, 1500 seconds was noted as it's time. Conclusions Having identified the anomalies, we can now analyse these results. As stated, the original experiment's results were as expected. Although we could never predict the timings, it was reasonable to expect the solutions to take progressively longer to clear. I believe that placing a 25 minute time limit was a reasonable action. Even though neither of the weak solutions - 1% glucose solution and "SAMPLE B" - became fully clear, I am confident that both solutions were at the same stage. I feel that once the time limit had elapsed, both solutions were a transparent, light brown-green colour. By looking at the graph, I can draw no other conclusion in regards to SAMPLE B than to assume that at most, there was no more than 1ml of glucose and 99ml of distilled water in a 100ml solution. That is to say, SAMPLE B was at most a 1% glucose solution. SAMPLE A is much easier to estimate. We can see from the original experiments that 9% had a time of 126 seconds and that the 8% solution had a time of 149 seconds. By looking at the graph, we can see that SAMPLE A has a glucose concentration of around 81/2%. That is to say 8.5ml of glucose and 91.5ml of distilled water in a 100ml solution. ...read more.
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