Catalase.
Catalase is a common enzyme found in plants and animals. Sources of it include fresh liver and raw potato, and is the fastest acting enzyme known. It breaks down hydrogen peroxide, H2O2 to water and oxygen.
Simple Plan:
In this experiment, I will investigate the effect of the concentration of the enzyme catalase on the rate of reaction with hydrogen peroxide.
- The source of catalase will be cubes of potato.
- In order to change the rate of reaction, the amount of potato cubes will be changed so the amount of hydrogen peroxide must remain the same throughout the experiment to make this a fair test.
- To measure the rate of reaction, I will collect the gas given off using either an upturned measuring cylinder in water, or a gas syringe
- After regular intervals of time, the amount of gas given of by the reaction will be measured and recorded.
- This will then be repeated with different amounts of potato cubes to increase or decrease the surface area.
The only variable that will change is the surface area of potato i.e. the number of potato cubes. The variables that will stay constant are the amount of hydrogen peroxide and by doing the experiment over a short period of time it can be assumed the room temperature will be the same. The same equipment and timers will be used which should help to ensure accurate results are obtained.
Preliminary Experiments:
In order to test the two methods of gas collection, experiments were performed to discover the potential advantages and disadvantages with each method. These experiments also allowed me to decide on levels of reactants, and to give basic results to allow predictions to be made.
These experiments allowed me to try the two methods of gas collection. I found that an upturned measuring cylinder was the best method because it could measure a greater amount of gas. Using a gas syringe was impractical because while the reaction was still happening, the syringe had reached full capacity. This would lead to poor results. Using smaller amounts of potato was not a viable option because the limitations of the syringe would have meant a variety of results could not be presented. When using the cylinder, it is necessary to use larger amounts of potato so the results can register on the scale.
One problem that became apparent during the preliminary experiments was being able to get a cube with a constant size. I decided to measure 1cm cubes and cut them with a scalpel but this was not a totally accurate method.
Predictions:
I think that more cubes of potato will cause a faster reaction because it will mean more enzyme will be present in the reaction. This is because there will be a greater surface area of potato therefore there will be more catalase present. I also believe that the reactions will start faster and will gradually slow down until they finish.
Method:
Equipment needed:
water trough
large measuring cylinder
delivery tube
Buchner flask and bung
scalpel
stopwatch
Quantities of reactants required:
80cm3 hydrogen peroxide per reaction.
1cm cubes of potato.
- Fill the water trough with water.
- Fill the measuring cylinder with water and place it upside down in the water trough. Ensure no water escapes, as the cylinder must be completely full of water in order to gain accurate results.
- Connect the hose and glass tubing to the conical flask and place the end of the glass tube under the measuring cylinder.
- Place a given amount of potato cubes in the flask and prepare the hydrogen peroxide.
- Mix the reactants and start timing, noting readings from the conical flask at set time intervals, e.g. every 30 seconds. It is very important to get the bung on to the conical flask quickly as without it gas will escape and results will be inaccurate.
- When the reaction ends, clean the equipment and repeat changing only the amount of potato cubes.
Safety:
Wear safety goggles as hydrogen peroxide is an oxidising agent.
Should any peroxide be spilt clear it up immediately. To lessen the chance of this happening, always replace the lids of containers.
In case of contact with skin, wash immediately to prevent irritation.
To prevent damage to clothes by the peroxide, wear a lab coat.
Take care when handling a scalpel as they are very sharp.
Results.
Surface area of potato 30cm2 in 80cm3 peroxide.
These are the average results for the experiment.
Rate of reaction = 57/10 = 5.7 cm3 per minute.
Results.
Eight cm3 pieces of potato; surface area of 48cm2.
80cm2 hydrogen peroxide.
Here are the average results for this experiment:
Rate of reaction = 74/10 = 7.4 cm3 per minute.
The rate of reaction shows the average speed of the reaction and is a useful measure when comparing many different reactions.
The results for this experiment are fairly accurate and close to the line of best fit. The first point is obviously away from the line of best fit. This happened because the measuring cylinder’s measuring scale started at 24cm3, so results beneath that were estimated.
Ten pieces of 1cm2 potato; surface area of 60cm2
80cm3 hydrogen peroxide.
Rate of reaction = 120/10 = 12cm3 per minute.
My results showed that my prediction was correct. Reactions with larger amounts of catalase were faster. This is because enzymes work on a ‘lock and key’ principle. Each enzyme molecule has an active site into which specific substrate molecules fit. If more of these enzyme molecules are present then more substrate molecules will be able to react. As more substrate molecules are reacting, then the reaction will be faster because more enzyme molecules can react with substrate molecules at any given time.
Hydrogen peroxide will decompose in air to form oxygen and water. Catalase is a catalyst for this reaction, and causes the reaction to happen much faster.
This table shows the reaction rate of each reaction and proves that reaction rate increases with enzyme concentration. The reaction rate shows the average amount of gas produced per minute.
This graph shows the results from each experiment.
I also predicted that the reactions would start quickly and slow down. This prediction was also true, and this is shown by the curve of the line of best fit, which has a slight curve. If the reaction had been continued, the curve would eventually flatten as the reaction finishes.
Evaluation:
I think the investigation was successful because I proved my prediction that a higher enzyme concentration makes a reaction faster. My results were accurate enough to prove my prediction.
In general my measurements were accurate. In the third experiment the results are not so accurate, and their pattern is more erratic. This is most likely caused by human error in reading the results from the measuring cylinder. A reaction such as this is faster and reading the results while the reaction is in progress is difficult. There may also have been problems with reading the meniscus. This is the curved shape of the surface of a liquid in a thin tube caused by surface tension. Results should be read from the base of the meniscus, but with bubbles breaking the surface of the water during a more violent reaction this makes accurate result reading very difficult. The results up to 24cm3 are not likely to be accurate because the scale on the measuring cylinder started at 24cm3, so all results lower than this were estimated.
The second and third experiments’ results were accurate as the points were near to the line of best fit.
The first two experiments were repeated twice. This was done so any anomalous results could be seen and noted. The third experiment was not repeated because the previous two experiments had proved my prediction, and the third experiment was close enough to the true values to reinforce this.
The results could have been improved by making the following improvements:
- There was a time delay in mixing the potato and hydrogen peroxide, which would have allowed gas to escape the Buchner flask and this could have affected the results.
- The measuring cylinders used for this experiment had a scale which started at 24cm3. this meant that results below 24cm3 were estimated
- I would need to find a way of stopping the reaction while I took the results. This could be done by kinking the delivery tube, so no more gas enters the measuring cylinder while a reading id being taken.
Improvements:
- The experiments could be run for longer. The reactions had not finished in my experiment, which lasted for 10 minutes. In my prediction I stated that the graphs would be curve shaped, but would gradually flatten as the reaction progressed. In order to prove this, I would need to run the experiments until the reaction finished. In my experiment, it was impractical to do this because it requires large amounts of time.
- As an extension to the experiment, it would be useful to test other sources of catalase for example liver. To obtain true values for the reaction between catalase and hydrogen peroxide, a pure sample of catalase could also be used.
