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

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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. In this experiment, as the temperature increases, the enzyme and starch molecules collide more frequently (Brownian motion) and with more energy which will cause them to react more efficiently. At low temperatures, the molecules will not collide very frequently and the starch will not be broken down as quickly.

It was predicted that the amylase would break down the starch most effectively at 40oC, and with decreasing efficiency towards 0oC, at which the amylase would be unable to break down the starch at all. This is because body temperature is around 40oC, and enzymes are designed to work at this optimal temperature. At temperatures over 40oC, it was predicted, the amylase would begin to denature to an extent that, at temperatures much over 50oC, it would be totally ineffective.

I also predicted that, with time, the starch concentration would decrease for each temperature tested, showing exponential decay so that, after every x minutes, the starch concentration would half and would therefore never be totally broken down. It was predicted that, if a graph were drawn to show starch concentration against time, it would be an exponential decay curve. The exponential behaviour was predicted because the reaction is not an equilibrium reaction: as the starch concentration decreases the enzyme finds it increasingly difficult to find enough substrate to act on. Although using iodine to test for starch would prevent a graph from being drawn in this way, the trend would still be evident.

The independent variable was temperature, controlled during the experiment. The variable dependant on this was starch concentration. All other variables therefore had to be kept constant to ensure that the experiment was a fair test. These controlled variables were concentration of amylase and starch in the solution, time period over which the experiment was conducted and the volume of amylase solution and starch solution. The apparatus was also kept the same throughout.

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I then decided to conduct the experiment as follows: Two test tubes would be taken, with equal amounts of starch and amylase solution. The contents of the two tubes would then be combined in a separate tube, and a timer started. Then, every minute, a sample of the mixture would be taken using a pipette, and placed on a ceramic tile. A drop of iodine would be added to each drop. The colour would be noted and a colorimeter used to measure the index of concentration. The index of concentration would then be noted in a table for each sample. ...

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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