- They are sensitive to pH: The term pH refers to the degree of acidity or alkalinity of a solution (denatured). Most enzymes work best in neutral conditions (i.e. conditions that are neither acidic or alkaline).
The diagram (below) shows how enzymes work. Molecules are constantly moving about and bumping into each other. When a substrate molecule bumps into the molecule of the right enzyme, it fits into a depression on the surface of the enzyme molecule. This depression is called the active site. The reaction then takes place and the molecules of product then leave the active site, freeing it for another substrate molecule.
The active site of a particular enzyme has a specific shape into which only one kind of substrate will fit. The substrate fits into the active site like a key fits into a lock. This is why enzymes are specific in their action. When an enzyme is denatured by heat, the shape of the active site is changed so that the substrate no longer fits.
Hypothesis:
Hydrogen peroxide will breakdown to oxygen and water in the presence of catalase. The reaction will increase with increasing enzyme concentration when molecules of hydrogen peroxide are freely available. However, when molecules of the substrate are in short supply, the increase in the rate of reaction is limited and will have little effect.
Prediction:
I predict that if I have a higher enzyme concentration, then this will bring about a higher rate of catalase activity. Because of this, there will be more places for the reaction to take place, which will cause more chemical reactions. Because of the cause of more chemical reactions it will result in successful collisions because of the active site of the enzyme and substrate.
I also believe that the longer the potato is left in the hydrogen peroxide solution the greater the reaction and that more oxygen will be released. I think at first the reaction will be rapid but as time goes on the reaction will slow down. This is because the hydrogen peroxide will start to become saturated and there will be less hydrogen particles to collide and therefore less oxygen to be produced.
Safety:
Whilst carrying out this investigation I will have observed and kept to the relevant safety rules. I will have worn goggles to protect the eyes from the hydrogen peroxide. A labatory coat will be worn to prevent chemicals from spoiling clothes. Care will also be taken whilst handling the chemicals, as hydrogen peroxide is corrosive. I will also keep all the apparatus away from the edge of the desk to prevent breakages.
Apparatus:
- Hydrogen Peroxide
- Cork Borer
- Water
- Scalpel
- Bung
- Chopping Board
- Stop Watch
- Beaker
- Delivery Tube
- Measuring Cylinder
- Conical Flasks (2)
- Potato
- Hydrogen Peroxide (10cm)
- Water
Diagram:
Variables:
- Controlled Variable: I must ensure that I keep the temperature the same, the amount of hydrogen peroxide the same amount and exact size of each potato cylinder the same size throughout this experiment, to keep the experiment equally consistent throughout.
- Independent Variable: I will keep everything the same as if it was a controlled variable, but I will change one element on each of the experiments –the amount of potato discs used.
- Dependant Variable: This is to see the amounts of bubbles resulting in the independent variable that I will have done.
- Confounding Variables: This will not apply to me, as I foresee that there will be no occasion throughout the experiment, that there will be anything present that will be beyond my control.
Plan (method):
Firstly, I will put on the relevant Labotary safety clothing. Next I will collect the relevant equipment needed for this experiment and then the equipment will be set out correctly, as indicated in the diagram. Next I need to ensure that both my work surface and apparatus are completely clean and ready for the experiment to take place.
Next, I will cut the potato into 5 equal cylinders (of equal size) in preparation for the experiment. Then I will place 10cm of Hydrogen Peroxide into a conical flask and then I will instantly place the bung with the delivery tube in it on the conical flask (this must be done so that oxygen cannot escape). I will then put 150cm of water into the other conical flask. Then I will take the bung off the conical flask with Hydrogen Peroxide in it, putting 5 potato cylinders into the Hydrogen Peroxide, and quickly put the bung back on, then put the other end of the delivery tube into the conical flask containing the Hydrogen Peroxide. Then I will immediately start the stopwatch.
Then I will count the number of bubbles that come through the delivery tube and out of the water. The time limit will be 5 minutes. I will also count and record the amount of seconds it will take between each new bubble appearing in each experiment, in the 5 minutes allocated.
Moving on, I will continue to do the experiment by using different amounts of potato discs. The first experiment will be 5 potato discs, the others will consist of: 10, 15, 20, 25 and 30 potato discs.
To make sure that it is a fair test, I will ensure of the following:
- I will do the experiment at room temperature.
- I will keep the amount of water used, constant.
- The equipment will be clean and dry after each experiment.
- The time will be kept constant, at 5 minutes for each experiment.
- I will continually record all finding whilst watching each experiment.
- I will constantly monitor all results on each experiment to ensure that I do not miss anything (to ensure that the results will be 100% accurate).
Results:
The results that I gained from the all 6 experiments are shown in the table below.
Graph:
Evaluation of Results:
My experiment was successful, but I could do more things in order to get more reliable results. If I had had more time, I would certainly do the experiment more times with different amounts of potato discs. I would have liked to do the experiment using different amounts of the hydrogen peroxide to see the affect it would have had on the same amounts of potato discs that I had already used in the experiments that I had done.
According to the results chart and the graph, there are no visible outstanding results.
If I had done the experiment more times and got a more precise average, then there may have been some outstanding results (for example, results that were too high or too low in comparison to the majority of the results).
Bibliography:
Upgrade A-Level Biology. Glenn and Susan Toole.
Biology – Nelson Science. Michael Roberts.
Biological Science 1. Green, Stout and Taylor.
Advanced Biology. Michael Kent.
