Preliminary experiment
Plan
In this experiment the effect of the surface areas of the potato will be investigated. A 6 cm length cylinder of potato will cut out and that cylinder will be cut different amounts of time for each trial. The first trial will use 3 2 cm length cylinders. The second trial will use 6 1 cm length cylinders and the third trial will use 15 0.5 cm length cylinders. I predict that the amount of oxygen produced will increase when the surface area is increased, as more catalase enzymes can move out of the potato in a certain amount of time.
Apparatus list
Measuring cylinder (25 cm³)
Boiling tube
Hydrogen peroxide of concentration 1%
Potato
Scalpol
Stop watch
Bung
Deleivery tube
Trough with distilled water
White tile
Ruler (any length)
Bulb pipette
Cork borer.
Procedure
The skin of the potato was cut using a scalpel on a white tile. Then a cylinder of the potato was cut using a cork borer. The cylinder was cut down to 6 cm in length.
The 6 cm cylinder was cut into 3 pieces of potato, each of them was 2 cm in length. This was done using a scalpel and ruler on a white tile.
One of the ends of the delivery tube was attached to the bung, so the end was exposed to the air.
The hydrogen peroxide was put into the boiling tube using a bulb pipette.
The measuring cylinder is inverted and put in the trough and is rested against the side of the trough. The trough was filled with water three quarters of the way up. The delivery tube (end not bung) was put in the trough and into the measuring cylinder.
The potato was quickly put into the measuring cylinder while somebody was holding a stopwatch. The stop watch was immediately started once the bung was placed onto the boiling tube. Another person was ready to count the bubbles of oxygen.
When the seconds on the stopwatch reached 30 then the amount of bubbles counted was recorded. This was repeated 3 more times. The 4 th result was taken just incase there were anomalies in the results.
This whole method was repeated for the other two trials, using 6 1 cm length cylinders and 12 0.5 cm cylinders. A new 6 cm cylinder of potato was used each time.
Results
Evaluation of preliminary experiment results
The results here do support my prediction but they are not accurate. There is too much variation between the results using the 2 cm pieces (26-18 = 8 bubbles) and the 0.5 cm pieces (36-29 = 6 bubbles). The difference between the average number of bubbles result for the 2 cm and 1cm trial is a lot less then between the 1 cm and 0.5 cm trial. These should be about the same, as the amount of enzymes leaving the potato doubles as the surface area doubles. So the difference between the results showing the average amount of bubbles produced should be consistent but is not, in this experiment.
Improvements to preliminary experiment.
Counting bubbles accurately in a exact amount of time is hard and makes human error have a bigger impact on the experiment. If volume of oxygen produced is recorded the human error will be smaller.
The time before a result is collected should be more than 30 seconds, as this should give results with less variation, as more gas is collected. Error gives a bigger impact on results if a shorter time is used. The result should now be recorded every minute.
A inverted burette held with a stand and clamp should be used. As the volume of gas is recorded, a burette is more accurate. It will be held with a stand as this makes human error smaller as it is easier to read the volume on the burette.
More trials should be taken out, as this provides less room for error and it is easier to see any anomalous result. It could be that one whole trial was done wrong, but with only 3 trials it is hard to see.
The degree of accuracy should be greater as this makes the experiment more accurate. So I will measure the results to the nearest mm.
The experiment should be repeated as this shows anomalous results more clearly.
There needs to be a control to make sure that it was the hydrogen peroxide being broken down that caused the oxygen, not anything else.
The apparatus is set up first, this reduces the catalase lost from the potato before experiment starts.
The repeats used the same potato used the first time and the same hydrogen peroxide solution. This means that substrate was used up before the repeat, so the oxygen production could decrease in the repeat. Also the catalase was already out of the potato in the repeat, so it started to break down the hydrogen peroxide quicker than in the first experiment. For the repeat, new hydrogen peroxide and a new potato will be used.
Method– Investigating the effect of substrate concentration on the enzyme catalase
From the preliminary experiment, I found the larger the surface area the larger volume of gas produced. The larger the volume, the smaller the impact errors have on the results. So I will use 12 0.5 cm pieces of potato from a 6 cm piece of potato (the circumference will be the same as the 6 cm cylinder is cut from a cork borer. I will use different concentrations to give me a wider range of results. These will be 1%, 2%, 3%, 4% and 5%. As before the same potato will be used for the whole experiment, as there could be variations in catalase concentrations between different potatoes.
Apparatus list
Burette
Boiling tube
Hydrogen peroxide
Potato
Scalpol
Stop watch
Bung
Deleivery tube
Trough with distilled water
White tile
Ruler (any length)
Bulb pipette
Cork borer.
2 Stands
2 Clamps
Test tube rack.
Procedure
The different concentrations of hydrogen peroxide solutions were prepared, 1%, 2%, 3%, 4% and 5 %
A boiling tube is prepared for each trial and the control experiment, and also an extra two for each trial and control for the repeats. This was done first to stop catalase escaping the cut potato. Boiling tubes are easy to label and store in racks. They were prepared by pouring the hydrogen peroxide in. The boiling tube that was going to be used was held in place using a clamp and stand.
The burette was held by a clamp on a stand and is inverted. The tap was off to prevent gas escaping. The burette was placed on one of the sides of the trough. The bottom of the burette without scales was put underwater. This is so the maximum amount of gas is collected. It was made sure no air got in the burette while it was inverted. The water was allowed into the burette so that it reached almost 0.00 cm³. This number was recorded at the start of each trial. The number is measured from the bottom of the meniscus for more accurate results.
The trough was filled with distilled water. If tap water was used, the chemical ions in it could affect the reaction.
The Delivery tube was fixed so it went under and into the bottom of the burette, in a way that no air bubbles get trapped.
This is done on a white tile. A 6 cm potato cylinder was cut using a cork borer. 12 0.5 cm cylinders are cut from the 6 cm cylinder. Any skin was cut from the potato to prevent the catalase getting blocked.
The pieces of potato were put into the clamped boiling tube containing the hydrogen peroxide. As soon as this was done the bung containing one end of the delivery tube was put on the tube. And then the time was started.
After every minute, the amount of gas collected was recorded. This was done by misusing the initial volume of water from the final volume of water.
Two repeats were taken out.
The last 4 steps were repeated for the two repeats for this concentration, and for the other different concentrations and their repeats. The boiling tube with the required concentration of hydrogen peroxide was clamped. Also the burette had to refitted to let the oxygen out.
Prediction
A predict that up until a certain point, the volume of oxygen produced will be directly proportional to the increase in substrate concentration. However after this point, the increase in oxygen production will start to decrease. This is because the more substrate molecules, the more the enzymes have to break down, so more substrate molecules are broken down in a certain time. However at a certain point there will not be enough enzymes to keep breaking down more and more substrate molecules in the same time, so the oxygen production won’t increase even if the concentration of substrate molecules increase.
