Investigation: Catalyse enzyme on hydrogen peroxide
I have chosen the experiment task; this is to investigate the effect of the potato disk catalyse enzyme on hydrogen peroxide.
Catalyses break down Hydrogen Peroxide into oxygen and water. Catalyse in one of the many enzymes that work bests between 30 and 40 degrees.
Variables to change and those to keep the same.

Change:

• Temperature
• Concentration of Catalyse (enzyme)
• Concentration of Hydrogen Peroxide
• pH.
• Size of potato discs / Surface area

I’ve decided to experiment with various temperatures.
The variables in the experiment that will change because of what I do are listed below:

• Volume of gas given off / evolved
• Time

The experiment is to measure the amount of oxygen given off over 10 minutes. This will be measured every 30 seconds.

Keep the same:
To ensure this is a fair test I will control the following variables and keep them all the same.

• Concentration – always using 20ml of Hydrogen Peroxide.
• Mass / Size / Surface area – using a special cutter and same part of potato
• Freshness of the potato.
• Time – same person timing and same length of timing.

I must keep the above variables the same. Otherwise there would be far too many changing measurements to monitor and the accuracy would not be as close to that of the fair test.

Hypothesis:
I predict that enzyme in the potato disks will break down the hydrogen peroxide fastest at the temperatures of approximately 37ºC (average body temperature)

I predict that the catalyse enzyme found in the potato will break down the substrate (Hydrogen Peroxide) the fastest at between 37 to 40 degrees Celsius because enzymes work best at certain temperatures, usually body temperature. If the temperature is above 40 degrees the enzyme will slowly become denatured so molecules of Hydrogen Peroxide won’t be able to fit into it and so they can’t form an enzyme substrate complex and can’t be broken down, so no oxygen or water is created. If it is below 37 degrees the amount of activity is reduced.

Apparatus:
Before I can begin my investigation I need to get all the apparatus I will need:

• Water baths of various temperatures
• Delivery tube
• Inverted measuring cylinder
• Boiling tube
• Stopwatch
• Potato cutter
• Stand, clamp and boss head
• Hydrogen peroxide
• pH7 buffer
• Potato
• Water trough
• Iced water (at 0º C)
• Test tube rack

Plan:
I will experiment with temperatures of 0º C first.
The water trough will be filled with iced water measuring a temperature of 0ºC.
An inverted measuring cylinder will be placed at one end of the water trough.
The delivery tube will then be connected to the bung, and the other end will go through the iced water into the inverted measuring cylinder.
The potato will be added to a boiling tube containing a solution of 50% hydrogen peroxide and 50% pH7 buffer solution.
As soon as the potato disks are added, the bung will be fixed on the boiling tube and the stop watch will be started.
The inverted measuring cylinder will collect any evolved oxygen and one can read off the measurements in the cylinder after the allocated time.
This experiment will be repeated three times for each temperature.
For all water bath temperatures, the boiling tube will be heated inside the baths measuring 40, 50 and 70º C.
For room temperature, the apparatus will be not set up in a water bath or trough.

Method for preliminary experiment:
The experiments were repeated once more for each temperature following the procedure above.
The results were recorded every 5 minutes.
Using the potato corer, some tubes of potato were cut, which were then cut into 5mm thick potato disks.
The measuring cylinder was filled to the top and was then carefully turned over and put into the trough of water. The clamp was then used to hold it in place.
The delivery tube was slid under the measuring cylinder.
The solution of 50% hydrogen peroxide and 50% pH7 buffer was added to the test tube.
The potato was added, the stop watch was started and the bung was replaced simultaneously.
Every minute for 5 minutes, the amount of oxygen evolved was measured.
This test was repeated once more for both temperatures.
After testing 2 temperatures, the following results were recorded for the preliminary experiment.

Preliminary Experiment
In order to test fairly and using appropriate variables, etc, I needed to carry out a preliminary test to see which were suitable measurements and times, etc, to take.
Here are my results for Ice water 0ºC
Time (minutes) Oxygen evolved from test 1 Oxygen evolved from test 2
1 0.4 0.3
2 0.6 0.9
3 1.4 1.3
4 1.6 1.9
5 1.9 2.1

Here are my results for 50º C
Time (minutes) Oxygen evolved from test 1 Oxygen evolved from test 2
1 0.4 0.6
2 1.6 1.8
3 2.0 2.3
4 2.8 3.2
5 3.8 4.2
From these experiments I decided that I needed to use more potato for a faster reaction and I decided that I should investigate more temperatures room temperature (23º C), 40º C, and 70º C as well as the already chosen 0º C and 50º C, so that I will have a good range or results.
I also decided to carry on my experiments, instead of using five minutes I chose ten minutes. And to repeat experiments so I have 3 sets of results per temperature to obtain a better average.

Obtaining evidence
I obtained my results by carefully following my plan and method. The results I obtained were as follows:
Temperature (ºC) Oxygen evolved from test 1 Oxygen evolved from test 2 Oxygen evolved from test 3 Oxygen evolved AVERAGE
0ºC (ice water) 4.3 4.2 4.4 4.3
23ºC (room temperature) 5.0 5.2 5.1 5.1
40ºC water bath 8.0 8.2 8.1 8.1
50ºC water bath 9.0 8.9 8.9 8.9
70ºC water bath 0.0 0.1 0.0 0.0

Analysis
I have drawn a graph which shows the average amount of oxygen evolved over ten minutes per temperature.
The graph shows that as the temperature is increased the reaction is faster and more oxygen is evolved, until 70C when the amount decreases. This is shown by the graph finishing in more of a straight line and this is because the enzyme becomes denatured and no more oxygen was produced because an enzyme “substrate complex” (as it is known scientifically) could not be formed. There seemed to be no anomalous results in this experiment.

The graph shows that the optimum temperature for catalyse is 50ºC. This is because at 70ºC the enzyme became denatured and could not form an enzyme ‘substrate complex’, therefore it produced no oxygen. At 0ºC and 23ºC there was less oxygen evolved because at lower temperatures the Hydrogen Peroxide molecules had less heat, and therefore less kinetic energy and so there were fewer collisions and fewer enzyme-substrate complexes were formed, so less oxygen was evolved.

Evaluation
My results are really reliable and accurate but they do not prove my prediction, which was that the catalyse would break down the hydrogen peroxide down best at a certain temperature of 37º C, when really it was at 50º C.
If I was to repeat this investigation, next time I would alter the following areas.
¨ more repeats of the experiment
¨ Checking bung regularly
¨ using a more reliable water bath
Overall, I think my investigation was successful.