Every enzyme has its own range of pH in which it functions most efficiently. Most intracellular enzymes function best at around neutral pH (pH7). Excessive acidity or alkalinity renders them inactive. On the other hand, certain digestive enzymes prefer a distinctly acidic or alkaline environment. For example enzymes that breaks down food molecules in the stomach work best at an acidic pH of about 2.
I predict that the more pieces or a bigger surface area of the potato that I use, the greater the amount of oxygen produced. The reason for this is because there is catalase on the surface of the potato; catalase is an extremely efficient enzyme, causing up to 200,000 reactions a second. So if there was a bigger surface area more catalase would be used up in the solution affecting up the rate of reaction, therefore making the hydrogen peroxide into water & oxygen in a matter of seconds.
Obtaining:
While doing the experiment, safety rules will be carried out as well:
(1) Tuck in tie. (2) Tie hair back.
(3) Wear Goggles. (4) Tuck in chairs.
(5) Stand up while doing the experiment. (6) Ask the teacher to refill the tube with hydrogen peroxide.
(7) Clear up spillages that are made in the work area.
In this experiment the amount of oxygen produced by the different surface areas of potatoes will be measured. The experiment will be done three times. Each time, the number of pieces of potatoes will be changed.
The method used for the experiment will be:
-
Collect the appropriate equipment; staling knife, potato (catalase), cutting plate, hydrogen peroxide, test tube, ruler, distilled water, stopwatch, and core borer.
- The potato will be cut out using the core borer. 30 mm of potato will be measured by using the ruler. They need to be the same length in order to make sure that the experiment is fair. The skin at both ends will be cut away so that all of the surface area is used.
20 ml of hydrogen peroxide is to be measured and put in the test tube. The test tubes used must be the same size so that there is room for the catalase to react with the hydrogen peroxide.
- The results will be recorded using the stopwatch. The amount of oxygen produced in two minutes will be recorded. After this is done, the test tube will be washed out with distilled water to get rid of the hydrogen peroxide or catalase. It will be repeated two more times so that an accurate average can be calculated from the experiment.
- After doing it three times with a 30 mm piece of potato, an average will be worked out from the three results recorded from the experiment. Another piece of 30mm potato is then cut in half making two 15mm pieces. The same procedure will be applied to the two pieces as it was done in step three (3.)
- The experiment will be done until six pieces of potato are cut.
Testing:
During the experiment, we collected results from how much froth (oxygen) was collected in two minutes. From the graph you can see that we have repeated the experiment two more times and then an average was calculated from the three results.
The experiment will be kept fair by using 20 millimetres of hydrogen peroxide in each experiment, using the same size test tube, and keeping the solution at normal room temperature.
These were the results recorded from the experiment
Fair testing:
In order for the experiment to be as reliable and as accurate as possible, we must ensure that it is carried out in fair conditions. This will enable me to make the most out of this experiment and help me to analyse the findings against my prediction. Firstly, it is important that all experimentation should be carried out in the same environment, in this case the same classroom. This will eliminate any changes in temperature or any other factors which could affect the experiment significantly. Similarly, it is important that all experimentation should be carried out on the same day. It is also very important that all equipment should be washed thoroughly after use; this will ensure that any reactants are washed away. If this was not to happen, the substrate and enzyme could begin to react before the stopwatch is started, rendering the experiment inaccurate. All measurements of substrates and oxygen froth will be taken from eye level to ensure we gain as much accuracy as possible. We will also make sure that the stopwatch is started and stopped as quickly and as accurately as possible. One of the most important features we must stick to is the cutting of the potato. All measurements must be taken with a ruler and using the scalpel the potato cylinder should be cut to the required lengths. Also, any skin left on the potato must be removed to ensure that the full amount of catalase possible is in contact with the substrate. Finally, we will use the same equipment in all experiments, particularly the same potato to ensure there is no room for variation in the concentration of catalase; this will leave no room for inaccuracy in equipment at all.
I believe that it is very important to carry out a fair test as the results of the experiment will be the basis for my entire coursework. Therefore, it is important that the results I get are as accurate as possible in order for me to make valid evaluations and conclusions. If I follow all of the fair testing points I have stated, the experiment will be very successful.
Finding the surface Area of a cylinder:
To calculate the area of the two circles;
2r²
To calculate the area of the cylinder
2rh
Where r is half of diameter. All radiuses were 5mm.
So
Analysis:
The data from the table indicates that as surface area increases, there is more hydrogen peroxide exposed on each potato and so more hydrogen peroxide would become oxygen and water.
In the graph there is a pattern between the combined surface area and the average amount of oxygen collected. As the surface area starts to change so will the amount of oxygen; the greater the surface area, the greater the amount of oxygen produced, in conjunction meaning that the smaller the surface area the less oxygen is produced from the solution.
In conclusion the data put in the tables show that the greater the surface area size of the potato, the more oxygen is produced in the test tube.
The complete surface area of the potatoes were not exposed to the catalase as in some experiments one piece of potato was covered by another piece of potato while in the test tube, this would stop some the catalase being used in the solution, thus affecting the rate of reaction.
The results were not very accurate as the rate of reaction didn’t reach its highest as some catalase was lost while the potato was being measured and cut. Also the potato lost some of the catalase because the potato was left out and was beginning to dry when other pieces of potato were being used for the experiment at the time.
Evaluation:
The results that were recorded from the experiment were partially inaccurate as not all things were kept the same, e.g. temperature, the amount of catalase. The experiment was carried out three times for different number of potato pieces. For example, three pieces of potato, two pieces of potato, and one piece of potato.
There was one anomaly on the graph as you can see; the last dot on the graph was not as straight as the other results were. It had raised five more millilitres then the other results have, the other results only raised an average of one millilitres of oxygen unlike the last result collected. This may be because the fact some residue of the catalase may have been left behind, if this were to happen it would be stuck to the side or bottom of the test tube till the next experiment is done and if it was a damaged cell the catalase would be released into the solution increasing the rate of reaction, thus making more oxygen or the level of hydrogen peroxide was inaccurate as it may have not been measured from eye level, thus making one anomaly. There was another reason why an anomaly occurred in the first place; this may be due to the temperature change as we did not finish conducting our experiment in one lesson, therefore having to conduct the experiment over a number of lessons.
Variations in my experiment:
Variables are relevant to this experiment all except surface area must remain constant in order to make the test fair. Alongside is an explanation of how I will measure these variables in an effort to keep them under control. For our experiment, we are investigating the dependent variable of how the surface area of an enzyme affects the decomposition of Hydrogen Peroxide; therefore the independent variable will be the amount of oxygen produced in two minutes when a piece of potato (containing catalase) is added.
There were variations during the experiment, the temperature of the experiment was not kept the same as the experiment was not completed in one lesson, and therefore having to do the experiment again over a number of lessons and the room temperature had changed between 20 – 30 degrees Celsius.
Another possible reason why there may have been a change in the results; the piece of potato may not have enough catalase in it because it was left out too long and was too dry for any moisture to stay on it. The experiment could’ve been done again to see if the same thing were to happen.
The results recorded could’ve been more accurate if the experiment was carried out four or five more times. This would mean that a better average of oxygen collected could be calculated and making the results more accurate as that is very important that I get the correct results.
The amount of hydrogen peroxide put into the solution could be changed to 30 or 40 millilitres instead of just 20 millilitres. This would change the rate of reaction and the amount of oxygen produced.
More catalase could have been added by cutting a longer piece of potato out; 30 millimetres to 40 millimetres, this way seeing what would happen to the amount of oxygen produced.
Problems that I encountered during the investigation:
When collecting the oxygen, some minor inaccuracies may have been caused when measuring the amount given off. All measurements were taken from eye level but although we were measuring the froth, the top of the foam may have been uneven, decreasing or increasing the amount by 1mm². Also, as we relied on the oxygen forming froth at the top of the solution, bubbles in the foam may have burst; releasing oxygen into the atmosphere and decreasing the amount of oxygen we were seen to collect.
Another problem that could’ve of caused inaccuracy in my experiment is that when the potato was dropped into the hydrogen peroxide solution, the potato would often stick to the sides of the measuring cylinder, or in some cases some cylinders of potato would often stick to each other in the solution. This could have rendered some of our results inaccurate as either the surface area was decreased as parts of one cylinder were covering parts of another, or that all pieces of potato were not in contact with the solution when the stopwatch was started. In a case such as this, we often repeated the same experiment when we thought it was necessary, and so I believe that not much accuracy was lost here.
Although we ensured that every item of equipment was washed in water after use, any residue left on the equipment could render the experiment invalid, also any water left in the measuring cylinder may have decreased the concentration of hydrogen peroxide or contaminated the experiment with chemicals used in water cleansing such as Chlorine. A possible solution to this could have been to use distilled water to wash all equipment with, thus any contamination would have been decreased.
Extending the Experiment:
If I were to extend the investigation further, I would find it interesting to investigate some of the other variables which affect the decomposition of hydrogen peroxide; some possible extensions are the effect temperature has on and also the PH of the solution. However, both experiments would need to be carried out in a specialist environment as they are both dangerous (hot chemicals) and also the use of acid. I would also find it interesting to compare different catalysts on the decomposition of hydrogen peroxide, such as manganese (IV) oxide or blood which both catalyse the decomposition. I would also choose to use my suggested experiment instead of the one we used in class to see if we are given any different results.
