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Investigating the effect of temperature on the breakdown of starch by amylase.

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Introduction

Investigating the effect of temperature on the breakdown of starch by amylase Planning The aim of this experiment is to investigate how effectively the enzyme amylase breaks down starch at different temperatures, and therefore to find the optimum temperature of amylase. Background theory relevant to this investigation involves enzymes in general, amylase itself and kinetic theory. Enzymes are a class of proteins which catalyse chemical reactions. Unlike nonbiological catalysts such as charcoal and platinum, which often need harsh extremes of temperature and pH, enzymes must work in the mild conditions of a cell in the body, at approximately 40oC and at a pH between 6.5 and 7.5. When compared with inorganic catalysts, enzymes are different in their rate of reaction (often 106 to 1012 the rate of the uncatalysed reaction) and in their specificity, their ability to act selectively on a small group of chemically similar substances. Chemicals changed by enzyme-catalysed reactions are called the substrates of that enzyme, and they fit into the active site of the enzyme, where the reaction takes place, in a lock-and-key mechanism. The products of the reaction then leave the active site, freeing it up for more similar reactions to take place. Amylase is an enzyme found in various places in the body including in the saliva and in the pancreas. It acts on starch, a polysaccharide, breaking it down into maltose, a disaccharide. Kinetic theory is the idea that, when a substance is heated, its molecules, having been supplied with energy, move around faster. ...read more.

Middle

A separate beaker was set up in which iodine solution was mixed with maltose. As maltose is produced when amylase digests starch, this would give an indication of the colour that the iodine would turn when there was no remaining starch in the test tube but just maltose. A sample was taken every minute and the same procedure repeated, until the iodine had reached the colour in the beaker, at which point it would be evident that there was no more starch. The time at which the starch had all been digested was recorded. This process was repeated twice for each of the temperatures 20oC, 30oC, 40oC, 50oC, 60oC and 70oC. Throughout the experiment, thermometers were used in each water bath to ensure that the temperatures remained constant. The following results were obtained: Temperature (oC) Time taken for starch to disappear (t minutes) 1/t 1 2 Average 20 9 15 12 0.0833 30 7 10 8.5 0.1176 40 5 6 5.5 0.1818 50 6 10 8 0.125 60 6* 12 12 0.0833 70 6* Denatures Denatures Denatures * these anomalous results omitted from averages Analysing Evidence In order to show the effectiveness of the enzyme rather than the time it takes to digest the starch, the inverse of the time taken to digest the starch was plotted on the y-axis, with temperature on the x-axis: The graph shows that, between temperatures of 20oC and 40oC, the efficiency of the enzyme increases with temperature. However, the graph between these points is a curve so the efficiency of the enzyme is not proportional to the temperature. ...read more.

Conclusion

However, with the samples collected, this colour was never reached and the readings were stopped after the solution turned a yellow/brown colour and stayed that colour. Had the experiment been undertaken with greater precision, it is likely that the yellow colour would have been reached. Finally, the procedure of preparing the solutions of amylase and starch for the experiment could have been improved. It is likely that there was some solution left over from the previous repetition of the experiment, making the starch/amylase ratio different each time. This could have been overcome by washing out the test tubes between readings. The volumes of each solution could have been made more accurate by measuring the solutions using a narrower gauge measuring tube or by using a syringe. An ideal solution would have been to automate the whole system, with a sample of the mixture being automatically taken every minute, or preferably more frequently, and the concentration of starch stored on computer. This would have overcome the inaccuracies of the timing, which could not always be exact using a stop clock and someone watching it, and would have eliminated the effect of human error from the experiment. If these steps had been taken, it is likely that a graph more similar in shape to that suggested in the prediction would have resulted. In conclusion, the accuracy of the results was certainly good enough to make a sensible conclusion. If the experiment had been conducted under more strict conditions and with more advanced instruments, the conclusion would not have been different although the individual results might have been more accurate and the graph might have looked very slightly different. ...read more.

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** It is difficult to assess this piece of work as it seems certain key sections are missing and the pages therefore do not follow on correctly.
To improve
Research and rationale
Examiners will be looking for a clear link between the proposed hypothesis and the biological knowledge and understanding described. In this case there needs to be a deeper discussion on the action of amylase and the biological explanation of the effect of temperature on the molecule. Suitably selected references should be included.
Planning
There needs to be a more thorough plan for investigation, with some explanation of the selection of apparatus and methods. (Part of the methodology section has been omitted and this makes following the report conclusions difficult). There are no details of how variables are to be controlled, manipulated or taken into account and how relevant observations are to be made.
The writer needs to identify more of the potential safety hazards and the steps needed to avoid or minimise should be identified.
A trial experiment should have been performed to help inform the planning.
A clear hypothesis should be stated.
Implementation
No results table had been included and this would lose credit. It would appear from the plotted graph that a sufficient range of data had been recorded but the conclusion implies only two replicates were carried out and these seemed to have varied a great deal. A statistical test of some description or manipulation of data is normally expected at A level.
Analysis and Evaluation
There is only a basic enzyme explanation for the data. The discussion needs to refer to the collision theory. References to

Marked by teacher Stevie Fleming 22/08/2013

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