- 1 potato
- 1 grater
- 1 scalpel
- 1 beaker
- 1 delivery tube
- 1 small conical flask
- 1 measuring cylinder
- 12 test tubes
- 1 stopwatch
- Hydrogen peroxide
-
D. Method:
A preliminary experiment was first done so as to determine the volumes, quantities and times needed.
The preliminary experiment was set up as follows. A piece of potato was cut and weighed. The mass was roughly 20g (to the nearest gram). This piece was then grated and placed in the conical flask. Water was added to the point where the grated potato was just submerged. The conical flask along with its contents was then heated in the water bath at a fixed temperature. The delivery tube was then connected to the lid of the conical flask. The measuring tube was then filled completely with water and placed upside down in a beaker of water (This method is based on the displacement theory which is later seen in the diagrams showing the concluded method). The other end of the delivery tube was then placed into the measuring cylinder. When the contents of the flask had reached the acquired temperature, 10mL of hydrogen peroxide was added to the contents. This was then timed for 5 minutes while the gas produced from the reaction (catalase and hydrogen peroxide) displaced the water in the measuring tube. At the end of the 5 minutes, the gas displaced was then measured and noted.
From this preliminary experiment, the following conclusions were drawn:
- 5 minutes was too long because to much gas was collected: the results would be false. So it would now be timed for 3 minutes.
- The conical flask used at first was too big and a smaller one would be needed as the gas produced wouldn’t displace the water fast enough.
- 10mL would be the required amount of hydrogen peroxide as the reaction seemed to be correct.
Therefore, the experiment would be carried out as follows. A piece of potato of approximately 20g was grated and this time, placed in a small conical flask. Water was then added to the point where the potato was just submerged. The conical flask along with its contents was then heated in the water bath at a fixed temperature. The concluded temperatures used in the actual experiment were 23°C, 30°C, 40°C, 50°C, 60°C and 80°C. The delivery tube was then connected to the lid of the conical flask. The measuring tube was then filled completely with water and placed upside down in a beaker of water (This method is based on the displacement theory which seen in the diagrams of experiment). The other end of the delivery tube was then placed into the measuring cylinder. When the contents of the flask had reached the acquired temperature, 10mL of hydrogen peroxide, measured with a measuring cylinder, was added to the contents. This was then timed for 3 minutes this time, while the gas produced from the reaction (catalase and hydrogen peroxide) displaced the water in the measuring tube. At the end of the 3 minutes, the gas displaced was then measured and noted. These results can be seen in the results section.
E. Variables:
- The temperature of the water bath was varied.
- The rate at which the enzymes broke down the hydrogen peroxide changed (this is an independent variable).
- The amount of potato, hydrogen peroxide stayed the same (this is a dependent variable).
F. Results:
The results were as follows:
(* for a 20g piece of potato and the reaction timed for 3 minutes)
The averages of the results are thus:
G. Analysis of the results:
The results seem to follow a certain pattern. The amount of gas produced from the reaction seems to start at a fairly low amount at room temperature. This amount increases as the temperature rises and it is at its optimum at 60°C. From then on, it falls. To illustrate this, graph 1 was drawn (see next page).
The results seem to support the prediction made. Temperature does have an effect on the rate at which proteins are broken down by enzymes. At room temperature, which is approximately 23°, the enzymes do not work as well as they should; their optimum temperature being roughly around 40°C or body temperature (where they are generally found). From the experiment, we can see that they work better at around 60°C. This indicates that as the temperature rises above that of the human body’s, the enzymes work faster because, as previously explained, they vibrate more and collide more often to the substrates and in doing so, are more likely to attach to the latter. However there is a limit to the temperature rise because at certain point, the enzymes will denature more rapidly. This is what is observed at 80°C. The enzymes have denatured as they have complied with the Q10 rule in which is stated that enzymes will denature once the temperature is high enough. As previously mentioned, the Q10 rule is calculated as a coefficient:
Q10 = rate of reaction at t + 10°C
Rate of reaction at t
So, we can now calculate the Q10 coefficient for all the results:
Most enzymes have a coefficient equal to 2, meaning that as the temperature doubles, so does the rate of reaction. As seen in the table, all the coefficients cannot be rounded up to 2. This will be explained later in the evaluation section.
Normally, the optimum temperature should be around 40°C but in this case, due to some factors (later explained in the evaluation section), the optimum temperature has skewed higher up the temperature scale. These factors will be explained in the next section.
H. Evaluation:
This experiment could have been carried out more accurately or in more precise conditions. Here are some improvements that could have been made:
- The amount of potato could have been made more constant, i.e. the potato could have been cut and weighed at exactly 20g at each experiment instead of rounding off the mass at the nearest gram (20g).
- The potato could have been isolated from the air as the latter may have dried the piece of potato up (and so enzymes would have been lost).
- The potato could have been grated in such a way that none of the actual potato itself would have been lost, i.e. no water or small piece was lost.
- The apparatus could have been more precise. For instance, the delivery tube could have been sealed better into the lid for the conical flask so as to not lose any air whatsoever. In general, the apparatus could have been made more scientifically accurate.
Some factors could have also been improved. Firstly, the potato could have been left longer in the water bath. Normally, enzymes work better at 40°C but as the results indicate, the optimum temperature of the experiment was 60°C. This could be explained by the fact that the catalase, i.e. the enzymes in the potato, had not been heated long enough so not much denaturing occurred and so the optimum temperature had skewed higher.
Secondly, some potatoes could have had more enzymes than others. This understandably is a factor beyond control but given the correct equipment (a scientifically accurate one) the number of enzymes could be controlled. However, it would take a very long time to get the same number of enzymes in each piece of potato.
Thirdly, the substrate, in this case the hydrogen peroxide, could have already broken down due to unseen factors. This could affect the result because in that case, when taking 10mL of it each time could mean that there was a lesser amount of substrate not broken down. So the amount of substrate could have been different.
A different experiment could have been carried out. A fixed amount of catalase is submerged in a fixed amount of water and heated for a fixed amount of time. After heating the catalase, an exact amount of hydrogen peroxide is poured into the catalase and water mixture. A measuring tube is then filled completely with water and placed upside down in a beaker of water (This method is again based on the displacement theory which will be seen in the diagrams of this experiment). The gas produced from the reaction (catalase and hydrogen peroxide) displaces the water in the measuring tube. At the end of a predetermined time, the gas displaced is then measured and noted. This method is effective in the sense that factors aforementioned are controlled further. For instance, when using the potato, the number of enzymes weren’t the same at each experiment. In this experiment, that number is now controlled as there is always a fixed amount of catalase. Also, when using the potato, enzymes could have been lost when it was exposed to the air. In this experiment, the catalase is in powder form so none are lost.
As previously calculated, the Q10 coefficients of the enzymes are more or less equal to 1.3 and most enzymes have a Q10 coefficient of 2. This could be explained by the fact that the experiment had some flaws aforementioned in this section. This could affect the prediction because, since most enzymes have a Q10 coefficient of 2, the coefficients calculated do not comply with the rule. So my prediction could be wrong. However, given these factors, the results do add up to a conclusion. Granted, the results are rudimentary (due to some of the factors previously explained) but there is a pattern: the rate does go up and having reached the optimum temperature, the rate does drop back down again.
So therefore, I can conclude that temperature does affect the rate at which the substrate is broken down.
