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An investigation into how temperature affects the rate of hydrolysis of starch by amylase.

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Introduction

Title An investigation into how temperature affects the rate of hydrolysis of starch by amylase. I am going to measure the rate of the disappearance of starch at different temperatures by observing the change in intensity of the blue colour formed by starch in iodine. The intensity of the blue colour is going to be proportional to the amount of starch present. The greater the change in absorbance between a sample of starch without enzyme (which is going to be my control) and the mixture containing the enzyme, the greater the amount of starch hydrolysed by the enzyme, therefore the greater the rate of reaction. Prediction I think that at 0�c the rate of reaction will be zero as I think no starch molecules will be hydrolysed, therefore the intensity of the blue colour is going to be the strongest when placed in iodine. After increasing the temperature from 0�c I think the rate of hydrolysis of starch will start to increase slowly then get faster, so that the rate of reaction doubles every 10�c. I think this will only happen up to 40�c, at which point the rate of hydrolysis of starch will be the fastest, therefore the intensity of the blue colour is going to be the weakest when placed in iodine as more starch will have been hydrolysed. After 40�c, I think the rate of hydrolysis of starch will begin to slow down rapidly and eventually stop completely at about 55�c, which again will produce the strongest intensity of blue colour when placed in iodine, as I think no starch will have been hydrolysed. ...read more.

Middle

If the shape of the active site of the amylase is disrupted then the starch molecules will not fit as well, and therefore decrease the rate of reaction. I do not think the pH will change very much, but to be certain I will use litmus paper to check that the pH remains constant. The time that we leave the amylase and starch molecules to react has to be kept the same. This is because keeping it longer at different temperatures will allow the amylase and starch molecules to have a longer time in reacting, so that one that has been kept in for longer will have more time to collide and form the enzyme-substrate complex and hydrolyse more of the starch than one that has not. I will keep the time constant by using a stopwatch and taking the colorimeter readings at the same time. It is important that these influential variables are kept constant as they could affect the validity of my results. This is because I will not be sure whether it is the temperature or some other variable that has given me a certain result. Apparatus 3 � boiling tubes to put the amylase solution into two of the tubes, and distilled water into one of them. 3 � boiling tubes to put the starch solution into and to put the amylase and distilled water when digestion is started. Thermostatically controlled water bath to accurately maintain the temperature at the eight different ones I am investigating. Test Tube holder to hold the boiling tubes and colorimeter tubes. ...read more.

Conclusion

Graphs I will draw my graph percentage starch remaining against time for each of the eight temperatures that I am investigating. I am going to use my calibration curve to look at how much starch has remained at the specific absorbances. I got my calibration curve by taking 12 boiling tubes. In the first one 0.5% starch solution was placed, then along the remaining 11 tubes the concentration of the starch was halved each time using water to dilute them, so that the starch concentration became less and less. Each of the 12 solutions were put into colorimeter tubes with iodine in and the absorbance was recorded. From the results, I drew a calibration curve; absorbance against starch concentration, so I was able to see how much starch remained at a certain absorbance. I think the trend I am going to get from my experiment is that the temperatures of 0?c and 60?c will produce a straight line on my graph of which the gradient is always zero and therefore the rate of reaction is zero. This is because I think none of the starch will be hydrolysed. I think for the temperatures 10?c, 20?c, 30?c, 37?c, and 40?c the curve of the graph will become steeper and steeper, with 40?c having the steepest curve. I think the graph for 50?c will be less steep than that for 37?c and 40?c. I am going to calculate the rate of reaction for each temperature by calculating the initial rate of reaction of each temperature, from the above graph. That is calculating the slope of the curve right at the beginning of the reaction by finding the gradient. ...read more.

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