All of the above factors will need to be kept the same apart from the temperature, as this is the factor I am investigating. This will make it a fair test.
Aim: To find the rate of reaction of Catalase in a potato with Hydrogen peroxide when changing the temperature.
Catalase:
Catalase is an enzyme found in every living cell (in animals and plants) and is one of the fastest working enzymes we know about. Catalase is one of the most potent enzymes known and can be found in places such as potato, yeast and tissues in the liver. Catalase catalyses the breakdown of hydrogen peroxide and works best at body temperature (37 Celsius).
Catalase: Hydrogen peroxide water + oxygen
2H2O2 2H2O + O2
Prediction:
I predict that when the temperature is increased the rate of reaction will increase, i.e. more oxygen given off. I think that beyond a certain temperature the reaction will not increase anymore and will decrease rapidly because the enzymes will become denatured. The enzymes will start to denature at around 50oc. I also believe that up to 40oc if the temperature is increased by 10oc the rate will be doubled.
Other results
I searched the Internet and found other results. This gave me a clear idea of what my results should be similar to. The results are below:
These results helped to establish whether my results were correct.
What I expect the graph to look like
In order to make the test safe I:
- Wore goggles
- Avoided any contact with the Hydrogen Peroxide
- Used a test tube rack
- Made sure I had enough working area
- Concentrated at all times
Apparatus
- Water baths
- Ice baths
- Test tubes/boiling tubes
- Measuring Cylinder
- Hydrogen Peroxide
- Potato
- Stopwatch
- Corkborer
- Plastic Tub
Method
- Cut a piece of potato using a Corkborer
- Put the piece of potato into a tube
- Measure out a certain amount of Hydrogen Peroxide and put it in the test tube
- Place the stopper on the tube and place the measuring tube into a tub of water
- Collect gas in the measuring tube and time how long it takes to collect a certain amount of gas
Measurements:
3 small cylinders of ready cut potato
15ml of Hydrochloric Acid
5ml of oxygen collected each time
The temperatures I will be using are (in degrees Celsius):
5, 45, 50, 70
My results
My graph (next page)
From looking at my graph I can obviously tell that my results are incorrect. I could also tell this from my results. My graph should have curved up and then when it reached a certain temperature it should have dropped. This is because the higher temperature would have caused heat energy causing more collisions and therefore the graph should have slowly curved up. Then after a certain temperature it should have fallen rapidly because the enzymes would have been denatured.
I have created another graph using results from a resource sheet. The table is below.
The graph is one page away (graph 2)
My first set of results were incorrect, this could have been due to various reasons. For example I could have timed it incorrectly. Also the temperature would have gone down throughout the experiment, the Hydrogen peroxide could have started at 50oc but eventually gone as low as room temperature. Which is why the method used for the results above was more appropriate. The experiment only lasted 30 seconds so there wasn’t enough time for the hydrogen to cool down.
I tried to make the test as fair and as accurate as possible. The potato in each test tube was the same size, the pH of the Hydrogen was the same, and the volume of Hydrogen was the same.
Conclusion:
From looking at the table and my graph I have observed that it has backed up my prediction. As the temperature rises there is more heat energy so the reaction is faster. Then at about 60oc the enzymes denature and the rate falls rapidly. The enzymes denature at about 60oc because the weak bonds, which hold the molecule into the specific shape for one substrate, are broken. The increase in collisions at higher temperatures is great enough to permanently change the shape of the active site. The enzyme is said to be denatured because it can no longer form an enzyme substrate complex as its active site has been permanently changed. There was very little activity in the ice bath because there were hardly any collisions between the molecules.
Evaluation:
In my method I had several problems. For example when I put the potato in the hydrogen peroxide the reaction instantly started, but I still needed to put the stopper on the test tube, this may have caused odd results. Also the measuring tube was hard to keep up and hard to keep full of water. Several times it slipped and the experiment had to be started over again.
I think all of my results were wrong especially when looking at them on a graph. These may be wrong because of the above reasons, which I have just explained.
I could have improved my method by somehow starting the reaction off after the stopper was placed on the test tube. This would have stopped the oxygen from being released and my results would have definitely been accurate.