The stronger the concentration of the hydrogen peroxide, the more particles there are in the solution – meaning that there will be more collisions between both the hydrogen peroxide particles and the potato slices (source of Catalase). The weaker the concentration of the hydrogen peroxide, the less particles there are in the solution – meaning that there will be less collisions between both the hydrogen peroxide particles, and the potato slices (source of Catalase).
A catalyst speeds up a reaction; it provides a surface where the reaction can take place. This increases the number of collisions between the particles of the substances that are reacting. A catalyst also lowers the activation energy – meaning that the particles can react with less energy than they needed to use before adding the catalyst.
In this experiment, I will be using Catalase, an enzyme.
Enzymes are very large and complex organic molecules that are synthesized by the cell to perform very specific functions. Catalase is an enzyme present in the cells of plants, animals and aerobic (oxygen requiring) bacteria. It promotes the conversion of hydrogen peroxide, a powerful and potentially harmful oxidizing agent, to water and molecular oxygen.
2H2O2 to 2H2O + O2
Catalase is found in a cell organelle called the peroxisomes. Peroxisomes in animal cells are involved in the oxidation of fatty acids, and the synthesis of cholesterol and bile acids. Hydrogen peroxide is a by-product of fatty acid oxidation. White blood cells produce hydrogen peroxide to kill bacteria. In both cases Catalase prevents the hydrogen peroxide from harming the cell itself. Peroxisomes in plant cells are involved in photorespiration (the use of oxygen and production of carbon dioxide) and symbiotic nitrogen fixation (the breaking apart of the nitrogen molecule N2 to reactive nitrogen atoms). Hydrogen peroxide is produced as an intermediate during these chemical processes and must be removed to prevent damage to cellular machinery. Aerobic (oxygen requiring) bacteria produce hydrogen peroxide as a by-product of metabolism. This fact is used when identifying bacteria. If hydrogen peroxide is added to a bacterial colony and bubbles are produced, this is evidence of oxygen production and confirms that the colony is aerobic.
Prediction;
I predict that as the temperature of the hydrogen peroxide increases, the rate of reaction with the Catalase in the potato will get faster. As enzymes denature or slow down when reacting at higher temperatures (as there shape is either destroyed or broken), I also predict that at 45°c, the reaction will either slow down or the enzyme will completely denature.
Method;
Firstly I collected my apparatus; a clamp stand, two measuring cylinders – one for the experiment and one for measuring the hydrogen peroxide, a water trough, a delivery tube and bung, boiling tube, thermometer and a stop clock. I set it up as below –
Having set up the apparatus as shown, before placing the measuring cylinder as in the diagram – I filled the water trough with water, and then completely filled the measuring cylinder, also with water, placing it securely upside down in the water trough with the clamp stand – being sure to keep the measuring cylinder full of water.
I then collected my reactants – 20cm³ of hydrogen peroxide, and 1 gram of finely sliced potato – being as accurate as I could when I measured the potato (managing to keep it within 0.02 grams above or below exactly 1 gram).
Having collected the potato slices and the 20cm³ of hydrogen peroxide, I went to collect the water for the beaker – which would act as a water bath for the hydrogen peroxide in the boiling tube. I added ice cubes, or boiling water from the kettle, to change the temperature to what was required for that test (either 10°c, 20°c, 30°c, 37°, 45°c), using the thermometer to check the temperature change. As it would be hard to get the desired temperature of the water, I used the water to the nearest temperature I could get it. Once I was as close as I could be, I placed the hydrogen peroxide into the boiling tube, placed it into the water bath (beaker) and placed the thermometer into the boiling tube and watched it until the temperature of the hydrogen peroxide met the desired temperature or close to it.
Once ready, I checked that the measuring cylinder in the water trough was full of water, and securely attached to the clamp stand. I also checked that the delivery tube was directly under the measuring cylinder. Having checked this, I put in the potato slices, quickly placed the bung on top of the boiling tube, and started the stop clock as I did so.
While watching the reaction, I kept check that the delivery tube was directly under the measuring cylinder – making sure it didn’t let off any oxygen other than into the measuring cylinder.
When the two minutes were up, I stopped the stop clock and removed the bung from the boiling tube. I then checked that the measuring cylinder in the water trough was vertical from eye, and read how much oxygen had been released into the measuring cylinder.
I re-did the experiment changing the temperature when needed, and making sure that each time, the potato slices were finely cut and roughly the same size as the experiment before.
The results are as shown in the table below –
Using the averages of each of the desired temperature, I have drawn up the graph below –
Conclusion;
Previously, I had predicted that at 45°c, the reaction would either slow down or the enzyme Catalase would denature. Looking at the graph above, we can clearly see that my prediction was incorrect, as the temperature increased, within 2 minutes, so did the amount of oxygen being produced. The only result which does not follow this rule, is at 30°c, where the amount of oxygen produced in 2 minutes has gone from 3.7cm³ to 3.5cm³. As this is not a major change in the amount of oxygen being produced, I am not that troubled with it – as the reason for this decrease could simply be that the temperature for each of the three tests of the water bath or the hydrogen peroxide was not exact to the desired temperature – causing an anomaly in the experiment.
At 45°c, the Catalase seems to have produced on average, the most oxygen within 2 minutes – it seems that it is here, that the Catalase works the best.
Not having done any further temperatures may have effected seeing exactly when it is that the Catalase denatures. It would only be safe to say that most probably; Catalase has another temperature at which it works the best, other than 45°c, and it would denature at a higher temperature.
Evaluation;
Having done this experiment, I would have preferred to have carried it out over a longer period of time – if I could have, I would have been able to do more experiments which could have shown a wider variety of temperatures and I would be able to see the optimum temperature that the Catalase would work at, and also see at what temperature the Catalase would denature at.
