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# The effect of temperature on the rate of an enzyme-catalysed reaction

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Introduction

BIOLOGY COURSEWORK PAVAN AULAK 11AV Interpretation and Evaluation The effect of temperature on the rate of an enzyme-catalysed reaction This experiment was carried out to see how the temperature of a protease enzyme (trypsin) and a protein (casein) have on the time it takes for the solution to become a colourless. The independent variable was the temperature of the trypsin and the casein. The temperatures (�C) we were hoping to measure were 10, 20, 30, 40, 50 and 60. The 10�C and 20�C water bath temperature was made by adding ice so they were not thermostatically controlled, as the ice continued to melt the temperatures could have varied slightly. The rest of the temperatures were thermostatically controlled so would have been more accurate. My dependent variable was the time taken for the solution to clear so that the 'x' was visible. The time was measured in seconds by a stopwatch. The controlled variables were the volume of milk solution, the concentration of the milk solution, the volume of trypsin and the concentration of trypsin. We divided into nine groups; we then all carried out the experiment once. By putting all our results together the data was more precise. We repeated the experiment nine times with six different temperatures, this enabled us retrieve a wide range of results. The following table is a raw table which shows my results. Time Taken for milk to clear /seconds Temperature /�C Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Trial 6 Trial 7 Trial 8 ...read more.

Middle

The temperatures when the solution became transparent were at 39�C and 49�C. The explanation why this happened is because enzymes work best at 37�C in the human body. This is called the optimum temperature. This is the correct temperature for molecules to have most energy and therefore collide more often causing the reaction to happen faster. The last phase which is very noticeable on my graph is that it curves extremely steeply from 50�C to 60�C; the time it takes for the solution to become colourless is much longer than the other temperatures. Above a certain temperature enzymes stop working and therefore the reaction stops this clearly not the case on my graph because the reaction does happen but takes a much longer time. At high temperatures the molecule will not fit in the enzyme so the reaction is unable to take place. The reason it does not fit is because the active site has been changed, the enzyme will have been denatured. Graph 2 is rate of reaction graph to show quickly the casein and trypsin reacts together. Generally the graph shows that the temperature increases the rate of reaction also increases, but when the temperature reaches 60�C the rate of reaction decreases dramatically. The graph is not directly proportional but it is almost proportional because as the temperature increases by roughly 10�C the rate of reaction also increases by roughly 0.01sec. The graph is not linear as the line of best fit is curved and all the points do not follow the same line. ...read more.

Conclusion

All my equipment was appropriate for the task, although it would have been better if we had more than one beaker so each temperature could have been done in a separate beaker as I believe that the previous temperature remained on the beaker which could have had an effect on the results. My results were accurate as I used a stopwatch instead of an ordinary clock. The divisions on the scale of equipment were adequate for the readings needed. From the equipment I used I expect the readings to be fairly accurate, although the water baths were quite big so I believe that there should have been more than one thermometer in one water bath as the temperature have been slightly different on one end to another. To make my results more accurate and reliable I would ensure that everyone did their experiment at exactly the same temperature and I would have left the solutions in the water bath a little longer so that temperature penetrated throughout the solution . To make my conclusion more certain I would do the experiment again but with 5�C so I could get a better understanding of what is happening during these temperatures. To conclude I believe that the experiment was a success and that my results are precise enough to make a firm conclusion that as the temperature increases the rate of reaction increases and the time taken for the solution to clear decreases but once the temperature has gone past 50�C the enzymes start to become denatured and the rate of reaction decreases and the time taken for the solution to clear increases. ...read more.

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### Response to the question

This is a great example of an investigation, with analysis of data being particularly strong. What I liked about this piece of coursework was the way the scientific explanation was integrated in with the data analysis. Generally at GCSE, students ...

### Response to the question

This is a great example of an investigation, with analysis of data being particularly strong. What I liked about this piece of coursework was the way the scientific explanation was integrated in with the data analysis. Generally at GCSE, students seem to think they must describe all the trends, then go onto a separate paragraph of all the scientific evidence. This essay describes each trend individually, simultaneously explaining why this is the case in reference to collision theory, etc.

### Level of analysis

The only downside of integrating the scientific analysis, as this essay has done, is that you have to go looking for it. I would like to see a few diagrams of collisions, or the lock-and-key hypothesis to guide the examiner to the analysis, and to show a fuller understanding of the scientific explanation. A few improvements could be made to increase the marks gained from analysis. For example, energy is referred to quite often, whereas commenting on the kinetic energy would show a higher level of understanding. A common improvement can be made when referring to denaturing - I always like to say that this is irreversible as the bonds holding the active site in its specific shape are now broken. Being able to explain that a substrate-enzyme complex cannot be formed, regardless of the temperature, will guarantee higher marks.

### Quality of writing

This piece is structured and formatted very well. The use of tables makes it clear to understand where the evidence is being taken from and the clear separation of paragraphs makes it easy to see the focus of each clearly. At times the sentences become overly long. I would always advise that in sciences the sentences are kept short and concise, to ensure you don't repeat yourself. This is especially key in the conclusion, where an essay is making its final impression on the marker. Unfortunately, this essay finishes with an extremely wordy sentence.

Reviewed by groat 11/02/2012

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