1. Using the cork borer, take a sample of potato, cut this piece in cm intervals using the scalpel and plastic rule. Then cut these a further 2 sections, so there is now 5 sections per 1cm piece of potato. Using distilled water; allow the potato discs to stick to the side of the glass Thistle Funnel.
2. Fill a beaker with about 4cm of the pre-made measured solution of Hydrogen Peroxide and using the graduated measuring cylinder, completely fill the 10 cm3 cylinder with the same solution.
3. Immerse the thistle funnel into the beaker with the steam below the surface of the Hydrogen Peroxide over the funnel stem.
4. Measure the volume of oxygen evolved in a time of 5mins.
5. Repeat the procedure with the other Hydrogen Peroxide solutions. Be aware not to contaminate each solutions with one another, this will cause inaccurate results.
6. Repeat all he tests at least three times (Time dependent) so that an average can be obtained. Repeating the experiments several times will help to produce better and more accurate results, as any inaccuracies in one experiment should be compensated for by the other experiments. Note all the results in a table such as the one below.
This gives the rate in cm3 of oxygen produced in the time of 5 minutes, this is because I am timing how much oxygen gas is given off in the space of 5 minutes for the various concentrations of Hydrogen Peroxide.
From these results, a graph can be plotted with concentration on the x-axis and the volume of gas released on the y-axis.
To ensure this experiment is completed as fairly as possible, all the variables except for the concentration of Hydrogen Peroxide must be kept the same for all experiments. Variables that must not be altered include:
Temperature, Catalase Concentration, dimensions of potato, air pressure and humidity.
When measuring the volumes of water and Hydrogen Peroxide, the measurement should be taken from a 90-degree angle to avoid parallax error.
Predictions
I predict that as the substrate concentration increases, the rate of reaction will go up at a directionally proportional rate until the solution becomes saturated with the substrate Hydrogen Peroxide. When this saturation point is reached, then adding extra substrate will make no difference.
The rate steadily increases when more substrate is added because more of the active sites of the enzyme are being used which results in more reactions so the amount of Oxygen released in a given time is higher. Once the amount of substrate molecules added exceeds the number of active sites available then the rate of reaction will no longer go up. This is due to the maximum number of reactions being done at once, so any extra substrate molecules have to wait until some of the active sites become available.
Results
I carried out the above experiment and these results were obtained.
H2O2 Conc. (Vol) 25 Vol 20 Vol 15 Vol 10 Vol 5 Vol
O2 Released (Vol) - First 2.00 1.84 1.46 1.11 1.00
O2 Released (Vol) - Second 2.03 1.86 1.50 1.13 0.8
O2 Released (Vol) - Third 2.02 1.86 1.47 1.11 0.90
Average of the Tests 2.0 1.90 1.5 1.1 0.9
The average results are all written down to one decimal place because it is very
Limitations
To enable this experiment to be completed as accurate as possible, I repeated it three times and then used and then used an average of all the results to best plot a graph with a line of best fit. I tried my best to keep all the variables apart from the one I was testing (Hydrogen Peroxide Concentration) the same.
However and unfortunately in practice it is impossible with the basic apparatus I had to keep all measurements precisely the same. For example:
1. There is a slight delay between pouring the thistle funnel with the potato discs into the beaker of Hydrogen Peroxide. This will slightly affect all the results for each individual experiment but as I carried out all the steps in the same way, it should not make any negotiable difference to the overall result.
2. It is also impossible to precisely measure out the amounts of Hydrogen Peroxide and Distilled Water each time. As the scale on the measuring cylinder shows the measurement to the nearest 1mm3, the solutions that I used should be correct to the nearest mm3.
Ways to Improve Experiment.
As using catalase founded in potatoes, the desired amount was hard to measure, however, measuring the amount of potato wasn´t difficult although that piece could contain different amounts of catalase compared to another piece. The results that would show from both pieces would be negotiable.
Maybe having a source of catalase from yeast would have been much more easier to use and handle. Specific amounts could be measured much more precisely.
