What equipment will I need?
For this experiment I think I will need
Test tubes a measuring a thermometer a weighing a scalpel
Cylinder scale
Some liver various tube’s a Bunsen burner a beaker hydrogen Stopwatch
Peroxide
Activation Energy’
For any reaction to start there is a minimum energy required to start the bonds breaking this is called ‘activation energy’ for a normal chemical reaction the hotter the reaction the faster it goes. The reason is that the extra heat ensures that the ‘activation energy’ is achieved more often and the rate increases, but after about 40°C, heat starts to have a destructive affect upon the enzymes.
We can show this upon a graph.
‘Activation Site’
There is a theory that each enzyme has an ‘active site’ which combines briefly with a substance and changes it by either splitting it apart or by linking two pieces together. The shape of the activation site fits only one
type of molecule, so each enzyme can only control one type of chemical reaction.
The set up of the experiment
Trial run
Before we started any practical work my teacher should me how to undertake the experiment she showed us the right weight of liver, hydrogen peroxide and water to use. She also established the set-up to use and how much time we needed.
What variables am I keeping the same?
In this experiment I will be doing, I think that it is important to keep all of the times the same, and the accuracy the same. Also I should carefully measure the Hydrogen Peroxide at the same levels as well as how much water there will be in the measuring cylinder. I think that the most important variables that I would keep the same are the timing with putting the bong upon the test tube and the weight and surface area of the piece of liver involved. The only thing that will be different is the temperature, which will range from 0°C to 80°C, this is how I will find the volume of oxygen.
The Method
At first I used a scalpel to cut a small piece of liver, I then measured it to about 0.9g, I made sure this was accurate and I thought I should use the same piece of liver during the whole experiment. This is because the surface of different size pieces of liver has different sized active sites. After measuring and cutting the liver I measured out 3ml of Hydrogen Peroxide, I then poured it into a small test tube and so I had it ready to be poured into the test tube containing the liver. I put both test tubes in a water bath to reach the temperature before adding them together. Next I placed the liver into the test tube and placed the test tube into the beaker. Then I connected the tubes leading from the bong into the other beaker, which was full of water. Next I filled the measuring cylinder with water and placed it above the tube. After the set up was done I quickly poured the Hydrogen Peroxide (3ml) into the top of the test tube containing the bong, started the stopwatch and placed the bong on top. After thirty seconds had passed I read the measuring cylinder, I then removed it and I removed the liver from the test tube. Next I repeated the test until I had the results.
How will I make the experiment safe?
During these experiments I will constantly be wearing safety goggles in case anything would happen to splash into my eyes, also I will be wearing plastic gloves when handling Hydrogen Peroxide and the liver. In addition I will be very careful whilst using the scalpel in case I should stab myself.
Obtaining Evidence
These results that I obtained were very different compared to what I thought that they would be. I think that it was a bad experiment because the results were low in comparison to that of an experiment in a biology book for example, but the results connected in a line of best fit and it does show the continuing half-loop as it does in many of the books.
Table of results
Analysing and considering evidence
What do the results show?
I think that the results show that after 40°C the ‘catalase’ enzyme itself starts denaturing because of the overpowering heat on it, that is why after 40°C the binding of the substrate to the ‘active site’ slows down because the key (substrate) cannot fit the lock (active site). This can be shown upon my graph because after 40°C it starts to slope downward quite rapidly.
Trends and/or Patterns
The results from this experiment are not extremely varied, and it does show promising patterns and trends, this is because the results do not stray apart, so they stay quite normal and do not drift. I think the pattern is supposed to be like a half-loop this is because after the mid point in the loop it starts to denature, this is when after a certain temperature heat causes individual strands to separate. Also the units them selves aren’t very wide-ranging, at the start of the graph the range is about 3ml whilst at the end of the graph the range is 6ml.
Conclusion
I think that the prediction I had was correct, this is because I predicted that after the optimum temperature of 40°C the reaction of ‘catalase’ with Hydrogen Peroxide would start to slow down, and therefore eventually stop the reaction from happening all together. This is scientifically proven because after 40°C the ‘active site’ deforms so the substrate cannot bind thus leaving the substrate unbroken and the ‘catalase’ enzyme useless, unless the temperature reaches around 40°C or less. I think that overall my original prediction does support my conclusion.
Evaluation
Was it a fair test?
In my opinion I think that the experiment was not very reliable or fair, this is because the timing used was unreliable and that the amounts and surface area’s were not reliable. Also the temperatures, which were a big part in the experiment, were not always exact, this can cause a lot of problems to do with the experiment as difference in the temperature of the water can cause inaccuracies in the measurement of oxygen produced
Were their any anomalies?
In this experiment there weren’t any anomalies this was because I would retest any odd results that I would have, this would make the test fairer.
Was the method reliable?
I think, although the units were not always precise the set up and method were both accurate. This because the results were all in a suitable range and that they weren’t anomalous temperatures
Improvements
There are a lot of improvements in my mind that could be done about the experiment for example:
- Tests should have been repeated and considered which would be more accurate.
- The amounts of liver, Hydrogen Peroxide, water and temperature should have also been considered.
- The timing of the reactions (30 seconds) could have been increased or decreased depending on the activity of the reactants.
Bibliography
Sources used in this presentation foundation biology (A-level) pgs 51-55, Microsoft Encarta’99, AQA biology pgs 10-11 and the Internet.
Sources used in this presentation, foundation biology (A-level) pgs 51-55, Microsoft Encarta’99 AQA biology pgs 10-11, the Internet.
