To get accurate readings I will first do a preliminary test to decide on a set of parameters to follow eg, the length of time the experiment lasts or the amount of catalase and Hydrogen Peroxide to use. If these parameters do not produce accurate results (eg, too much gas given off to record or reaction too fast to trap all the gas), I will change one of the parameters until the results can be recorded accurately.
Also, making a control experiment will show that there are no other contributors to the result. I will do the experiment with only the celery and then with only the Hydrogen Peroxide to make sure that it is not these that produce gasses on their own. I will also use the bottom of the meniscus when measuring liquids.
For reliability I will repeat each test, at each temperature, three times making at least 15 tests. If I find, as I am plotting my results, there it a reading that does not fit the expected pattern I will repeat that test for a fourth time.
Prediction: I predict that the higher the temperature the more gas will be given off up to a certain point. Therefore the faster the rate of reaction until this point. After this optimum temperature I think the rate will slow down to almost nothing and less gas will be produced.
In order for the reaction to take place you need to mix the two chemicals together. The temperature of the reaction is linked to the energy the particles have. If there is more energy, the probability of them colliding increases therefore the amount of reactions taking place increases. Also the amount of the products increases.
The reaction will slow down after a certain point because the energy given to the H2O2 particles (affected by temperature) is so great that collisions cause the catalase to be changed. The word given is denatured and this means that the active sight of the enzyme is changed so that it cannot react with its specific substrate. Also below the optimum temperature means that less energy is given to the particles so reactions become less frequent.
I found this information in ‘The Salter’s Approach’ Biology, the G.C.S.E revision guide, Advanced Biology Handbook by W.R.Pickering, and Biology 1 by Mary Jones.
To make the experiment safe, I will:
- Make use of safety equipment like aprons and goggles,
- Execute the experiment sensibly and efficiently,
- Make sure everything is ready before the experiment begins,
- Plan ahead so I know exactly what I am doing to avoid confusion.
Apparatus:
Observations:
Results:
* = Anomalous result ® = repeat
Analysis:
To display the information in a way I could analyse the results I put them into a graph.
A graph to show the relationship between the Temperature and amount of oxygen produced
= Line of best fit The optimal temperature for this enzyme
---------------- = Expected pattern is somewhere between 50 and 60oC
Finding that the results were quite accurate I went on to make a graph of rates to help find a pattern.
I found the rates by using the formula:
Variable Amount of Gas
Rate = ------------ = --------------------
Time 20 Seconds
First I made A Table of Rates:
The word and chemical equations for this reaction are:
Catalase + Hydrogen Peroxide Oxygen + Water
Catalase + H2O2 O2 + H2O
A graph to show the relationship between the Temperature
and rate of reaction
---------------- = Line of best fit
This graph clearly shows a bell shaped curve with a sharp fall, my prediction was therefore correct. In the 10-50 degree scale, as the temperature increases the oxygen produced increases and therefore the rate of reaction increases. This means it is a proportional reaction. After this point, between 50 and 60 degrees, there was a sharp fall in the rate of reaction. This was due to the active sights of the enzymes getting damaged and no longer being able to react with their specific substrate. This is called denaturing.
The rate increases up to 50 degrees because the reactions become more frequent as the temperature increases. This is because the particles of Hydrogen Peroxide gain energy as the temperature increases and so there is a higher probability of them hitting a particle of Catalase. Therefore there are more reactions per second, more oxygen is produced, and the rate of reaction gets faster. After 50 degrees the reactions between the Catalase and Hydrogen peroxide become so violent that the active sight of the enzyme (Catalase) is damaged and distorted, disallowing the substrate (Hydrogen peroxide) to react with it. There is almost no reaction after this point because an enzyme only has to be denatured a bit and then it cannot react with its substrate at all.
The results I got were accurate and reflected what I wrote in my prediction.
Not all of the results I got followed the expected pattern. For instance test C at 50oC showed an inconsistent result as marked in my table. This could have been caused by air already in the delivery tube causing a delay in the gas getting to the measuring cylinder, and therefore there being lass gas collected and measured. Also I had another set of results for 30oC. These were a lot different to the expected pattern and were not accurate enough to draw a conclusion so I repeated the whole test again and received better results. This anomalous result could have been caused by a number of different reasons, such as the equipment used was poor and inaccurate, the celery may be in different conditions, holoenzyme activity, alloenzymes, and inhibitors. The equipment was poor because the most accurate divisions available were millilitres. Also when the chemicals were mixed some of the oxygen may have been lost before the bung was put in. The condition of the celery may have had an effect because each lot we used could have come from a different supermarket, been a different batch, been different ages, or even come from different countries. Also fertilizers, and
pesticides may have been used on the celery leaving a chemical residue or changing the enzyme in a way to make it less efficient. Holoenzyme activity is when a proportion of the enzyme is adapted for different conditions like pH or optimal temperature. Alloenzymes are the same enzyme but maybe from different parts of the plant so they have a different working. This may have caused a less efficient and slower reaction. Inhibitors are more complicated but can change results dramatically. Competitive inhibitors compete with the normal substrate for the active sight. Irreversible inhibition is when the inhibitor does not quite fit and distorts the active sight rendering the enzyme useless. Non-competitive inhibitors bind with another part of the enzyme other than the active sight and distort it. Any or all of these reasons may have contributed to the strange results I got.
To get accurate results I repeated the tests 3 times. The results were slightly different each time but the lines of best fit are almost the same for tests A and B. Test C is different. The test A results were the best of the three because they fitted the expected pattern better.
Tests A and B follow the expected pattern but test C does not on two occasions. Both of these can be accounted for in my explanation above because they are both below the expected pattern.
I made a graph to show the difference
A Graph to show the relationship between my first set
of results and repeats
* = Anomalous Result
= Line of best fit
--------------- = Expected Pattern
My results could have been better if the third test had gone like the other two because I would have had more evidence to form a better pattern. They were quite accurate and did support my prediction almost perfectly with a nice bell shaped curve. However they are only accurate to the degree of accuracy I could use. For instance the smallest measurements were millilitres. However even with this defect I read the results accurately and I could use them to support a conclusion as I used an average of my results in my explanation.
The method for this test could be improved by having better equipment. This is because some of the gas was lost at the beginning of the process. This could be avoided, meaning the results would be better, if the chemicals could be mixed in a sealed environment. An Automatic Gilson pipette could be used because they are reliable and are very accurate in measuring liquids. Also, to create a water bath with a fixed temperature I had to use a combination of boiling water and cold water. This is accurate to a point but could be better with a thermostatically controlled water bath, where the temperature can just be set. This would also allow for a much larger range of readings. The measuring cylinder could be replaced by a gas syringe, which can measure to a better degree of accuracy giving better readings.
Also the test could be repeated several more times with a wider or more concise range of readings taken. This would produce more accurate results and the more points on a graph you have the more accurate you can be.
For additional information you could extend the test further by testing to see what happens to the rate of reaction after 60 seconds.
This experiment could be applied to the human body. Hydrogen Peroxide is a poison to the body and needs removing. For this reason the liver produces catalase to break it down. Therefore the experiment could have been conducted using ground up liver. It could also be applied to other enzymes in plants to find the ideal growing temperatures that could lead to increased or decreased production.
An extension could be made on the experiment by investigating what effect some of the other variables have on the reaction, such as concentration and pH. With these results I could form an ideal condition for the enzyme catalase in celery.