Catalase is an enzyme found in food such as potato and liver. It is used for removing hydrogen peroxide from the cells. Catalase speeds up the decomposition of hydrogen peroxide into water and oxygen. It is able to speed up the decomposition of hydrogen peroxide because of the shape of the hydrogen peroxide molecule. This type of reaction where a molecule is broken down into smaller pieces is called an anabolic reaction.
When there is an excess of enzyme molecules, an increase in the substrate concentration (salt solution), produces a corresponding increase in the rate of reaction. If there are sufficient substrate molecules to occupy all of the enzymes´ active sites, the rate of reaction is unaffected by further increases in substrate concentration as the enzymes are unable to break down the greater quantity of substrate.
Hypothesis
My hypothesis is that if hydrogen peroxide is mixed with catalase (in this case liver), water and oxygen will be given off. This should cause bubbling.
Apparatus
-twenty four beakers
-grease pens
-measuring cylinder
-1.5% hydrogen peroxide (H2O2)
-distilled water
-burette
-potassium permanganate
-liver (catalase)
-sulfuric acid
-stop watch
-tweezers
-salt solutions (concentrations of 0.5%, 1%, 1.5%)
Method
1. Take two beakers and using the grease pens write “baseline 1” and “baseline 2” on them. Using the graduated cylinder, put 10ml of H2O2, into the baseline 1. Using a pipette add exactly 1ml of water into the same beaker. Add 10 ml of sulphuric acid and mix well. Extract a 5ml sample from the beaker labelled baseline 1, and put it into the beaker labelled baseline 2. Then, using the burette, add a drop of potassium permanganate at a time into the beaker until a persistent brown colour is obtained. Swirl the solution after each drop is added. Record how much potassium permanganate was used to obtain the brown colour, this is called the baseline reading.
2. Now, Take five of the twenty two beakers and label them 10s, 30s, 60s, 120s, and 180s. Arrange them into a line, from lowest to highest. Put 2ml of the 1.5% H2O2 solution into each beaker, and using the pipette add 2ml of water into each one as well. Also add the catalase, which is a small cube of 0.5cm2 of liver, into each of the five beakers. This has to be dropped in at the same time for each beaker and the stop watch should be started. After 10 seconds using a measuring cylinder measure 10 ml of sulfuric acid and add it to beaker labelled 10s, in order to stop the reaction in that beaker, all the while letting the time run continuosly. After 30 seconds do the same (add 10ml of sulfuric acid) to the 30s beaker. After 60 seconds, do the same with beaker market 60s and so on until you are finished with all the beakers. From these solutions now remove the piece of liver using tweezers and add the potassium permanganate using a burette drop by drop untill each solution turns brown. Once again record the results. This so far is the control, record how much potassium permanganate was added to get the brown colour.
Now do part 2 once again using the 0.5% salt solution instead of water for the first repetition, using the 1% solution instead of the 0.5% salt solution for the second repetition and lastly using the 1.5% salt solution for the last repetition.All results should be recorded in a table.
Variables
The concentration of salt solution used differs for each test, this is the only variable.
The volume of solutions and catalase used always remains constant as well as temperature.
Results
Conclusion
The results show that as the enzyme catalase is left in each beaker for a longer period of time, less potassium permanganate was needed to neutralise the hydrogen peroxide left over after the breaking down of it with catalase. The amount of pottassium permanganate used is equal to the amount hydrogen peroxide that remainsafter it has been broken down by the catalase (liver). When the pottassium permanganate has turned the solution brown, this eant that it had neutralised the hydrogen peroxide and therefore their volumes were equal. The concentration of salt solution where the most hydriogen peroxide has been brocken down is the 1.5% solution. This was the optimum concentration for breaking down hydrogen peroxide The enxyme in this experiment was the catalase (liver), the substrate was the hydrogen peroxide and the products wer water and oxygen as predicted.
Evaluation
On the graph, it is clear that there are a few anomalies since as time increases each point should be lower showing a smaller amount of hydrogen peroxide present since more of it is able to break down in more time. Tese mistakes could have been eliminated by doing the experiment at least three other times, although this would have taken a long time. Also, the addition of sulfuric acid may have altered the test since this is an extra volume of acid present to be neutralised. However, stopping the reaction is essential so it is a remaining problem.
Bibliography
-Advanced Biolody book, 3rd edition
-Encarta Encyclopaedia (cd-rom)
-Biology for Life book