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

Analysis Of Results

As you can see from the processed results in the table above and the graph the experiment carried out was not the most accurate. The graph demonstrates that the first few readings are similar to that of the predicted results, however they soon fail to match the ideal results, which are illustrated in the graph below. This experiment can only be described as imprecise. As the experiment was carried out it became clear that there could be many improvements made to the method.

Cambridge Advanced Sciences Biology 1 P47 Figure 3.7

Since these results do not emulate the theoretical results it can be assumed that many inaccuracies were present within the method. A huge error in the results will be due to the lack of equilibration between the enzyme substrate solution and the water bath temperature. This will mean that the temperature being tested was not the one stated in the table. This means that as the water bath got hotter the quicker the enzyme substrate solution got to its optimum temperature of 38ºC. This explains the gradual increase in the rate of reaction as the temperature of water bath got higher rather than seeing a peak at 38ºC and then a swift drop as the enzymes were denatured. As you can see this graph contradicts the theoretical results giving an impression that as the temperature increased so did the rate, a near perfect positive correlation.

Evaluating procedure and equipment

All of the equipment used in every experiment has limitations. In any experiment there is a need for accuracy and precision and as you will see this experiment undoubtedly has many. By identifying and adjusting errors in the method and taking the limitations of the equipment into account a new method can be proposed which minimises significant sources of error and promotes attaining reliable results.

Suitability and accuracy of each piece of equipment:

Water baths: For temperatures 20ºC to 50ºC water from kettles were used for water baths and the temperature was brought down by the addition of tap water. For temperatures 60ºC and 70ºC electrical water baths were used. This was already posing a large threat to the fairness of the practical. The kettle water bath temperatures were not kept constant like the electrical water baths. This meant that the enzyme was not necessarily working at the temperature being examined. Also, the method of using the water baths was faulted. The method states to add the bottle of milk and trypsin tot the water bath once a constant temperature has been reached. This meant that the actual temperature the enzyme was working at had not yet adjusted to the required temperature. As the required temperature got higher the more time the enzyme-substrate solution needed to adjust to the temperature. However time for this adjustment was not taken into account, resulting in a massive inaccuracy. A suggested improvement is to use electrically controlled water baths for all of the temperatures tested and to allow for the enzyme-substrate solution to reach the temperature of required reading, equilibration. The use of electronically controlled water baths will ensure that the temperatures for each variable are kept to at the correct level, unlike the kettle water baths, which will continue to fall in temperature. Equilibration will mean that the substrate will be at the temperature being tested, not just the water bath and therefore the enzyme will be working at the required temperature.

Thermometers: The degree of accuracy on the thermometers was to 0.05ºC. This is an accurate piece of equipment however the method of taking readings needs to be correct. It must be read off at eye level so the meniscus is taken into account. The bulb of the thermometer must also be in the centre of the water since convection currents could affect the accuracy.

Syringes: Accurately used to 0.25cm³. This piece of equipment is accurate unless a syringe is mixed up and contaminated with hydrochloric acid when it is used for measuring the volumes of milk. A contamination between the hydrochloric acid and milk meant that the milk would have already started to be digested before the trypsin was added. Leading to further inaccurate readings. Ensuring that you knew which syringe was for which solution would be an improvement on this method, also a smaller scale would be better so that a reading could be taken much more accurately than to 0.25cm³.

Colour standards/method of judging end-point: Unlike length or weight there is no physical scale for measuring colour, making it unlikely that two people will answer in the same way when asked to judge this end point. Additionally, many factors can influence human perception of this end point such as age, eye sensitivity, mood, medications, light sources, object size, texture, directional differences and background elements. This method of using controls of milk and distilled water and milk and hydrochloric acid was suitable to a certain extent, however it could be improved upon. The use of a colorimeter or even a method of drawing a cross on a piece of paper and stopping the experiment when it is visible. Therefore this method had a fairly low degree of accuracy.

Timers: This piece of equipment has a degree of accuracy to 100th of a second, however the method under which it is used is also imprecise. The question is whether to start the timer when the first drop of trypsin hits the milk or the last drop, and is it physically possible to do these two things at the exact same time. However it is difficult to suggest improvement, unless you could get a partner to start the timer just as the first drop of trypsin hits the milk so that there is a more precise reading without a gap in the time it takes to move from the syringe to the timer start button.

Repetition: There was no mention of repetition in the method for this experiment. Indicating that any of the results could be anomalous and none of them can be guaranteed as accurate. This method therefore rules out human error. However this may be accounted for when a graph is drawn up. Anomalous results can be singled out and in this case there is certain fault in the shape of the graph.

After identifying many sources of error within this experiment it is clear that the validity of the evidence is challenged and will mean any conclusions drawn from this experiment will be imprecise and have little evidence to support them.