To meet health and safety regulations I wore goggles and washed my hands after the experiment. Before the experiment I researched what apparatus I need. I also researched what ranges of temperature will be suitable for my experiment. To find out what ranges will be suitable I carried out a preliminary investigation but I only obtained four results, as time was limited.
These five results already have started a pattern and is as follows; the higher the temperature the more oxygen produced. This pattern is only limited up to 45ºC mark as after this mark the enzymes denature and stop working properly therefore less oxygen is produced.
Method
To carry out this experiment first I put on my goggles and then collected all the apparatus that will be needed to carry out this experiment. I then measured out 50 ml of hydrogen peroxide and heated it to the necessary temperature. Once this was done I weighed out the potato sample. Removed all the skin on the potato and placed it in the flask with the heated peroxide. A bung with a tube was placed in the flask to stop any oxygen escaping and make it travel one direction and stop the heat from escaping. However not all the heat could be stopped form escaping as the flak was not insulated. This meant that heat could be lost through the flask. A measuring cylinder was filled with water and placed up side down in a margarine tub, which was also filled with water. This meant that no water could escape from the measuring cylinder. The end of the tube that was protruding the bung was directed into the measuring cylinder, which was filled with water. This meant that any oxygen given off travelled through the tube and into the measuring cylinder pushing the water out. This gave an accurate measure of oxygen. I decided that 10 minutes would be a reasonable amount of time as my time was limited and this would be enough time for the reaction to take place. During this experiment the flask was shaken gently every 2 minutes to ensure all the peroxide particles had reacted with the catalase. Once the time was up the amount of oxygen produced was measured and recorded. This process was then repeated for 35 times. Each temperature measurement was repeated 5 times to with 6 different temperatures to eliminate any anomalous results, which some times occur, in experimental errors. This would then ensure the experiment was fair. I must also ensure any variables which I planned to keep constant were constant as this could also produce anomalous results.
In the table below I have calculated the average amount of oxygen produced.
These results follow a pattern and is as follows; the higher the temperature within the stable mark the more oxygen will be produced. This corresponds to my prediction, which is, the higher the temperature the more oxygen is produced until 45ºC. Up to about 40ºC the rate increases smoothly and reaches a plateau, which is the peak where the optimum oxygen is produced at a certain temperature. An increase in temperature increases the movement of particles therefore increasing the number of collisions between the catalase enzyme and peroxide particles to allow a successful lock and key bond as illustrated below.
After this optimum temperature the rate of oxygen produced decreases rapidly as the temperature increases. This is due to the enzymes denaturing and changing the shape of their active sight and not allowing the key to fit the lock hence the reaction rate decreases affecting the rate of oxygen produced. The substrate can be represented by a lock and the enzyme by a key. Only one key can fit the lock. The key will open or close the lock just as an enzyme will split or unite substrate molecules. The combination of substrate and enzyme is very exact. Each enzyme molecule has a precise place on its surface, the active sight, to which the substrate molecules become attached. Every enzyme has its own particular shape. The shape of the active sight, and the positions of the different chemical groups within it, ensure that only those substrate molecules with complementary structure will combine with the enzyme.
Enzymes are not destroyed by the reactions they catalyse and can be used again the reaction is also reversible.
An enzyme can work in either direction. Metabolic reactions are reversible and the direction in which they proceed depends on the relative amounts of substrate and products present. The reaction will proceed from left to right until an equilibrium is reached between substrate and products.
A + B C
If for some reason a large amount C is present the reverse reaction occurs, C is being split into A and B until again equilibrium is established. The enzyme responsible for this reaction will catalyse it in either direction depending on conditions. The enzyme has no effect on the equilibrium point; it merely speeds up the reaction until equilibrium is reached.
The enzyme catalase is present in blood to prevent the build-up of dangerous peroxides. The catalase acts as a catalyst and speeds up the decomposition of hydrogen peroxide.
2H2O2(aq) 2H2O(l)+O2(g)
Catalase is an extremely effective catalyst. One molecule of catalase will decompose 40000 molecules of hydrogen peroxide each second. However unlike chemical catalysts, which work under a wide range of conditions, enzymes are only able to work under limited conditions.
The possible precautions which may be met in attempting to collect reliable data are making sure you keep all variables constant throughout each experiment for example the mass and surface area of potato uses, the concentration of peroxide, amount of peroxide etc. This is to ensure that the temperature is the only variable that affects the production of oxygen.
Up to 40ºC the amount of oxygen increases smoothly, a ten-degree rise in temperature being accompanied by an approximate doubling in the amount of oxygen produced. Above this temperature the amount of oxygen begins to fall off, and at about 60ºC the reaction ceases altogether. This is because proteins and therefore enzymes, at high temperatures are denatured.
With the apparatus available the accuracy of my method was high, however the errors that could have been made are pip-petting errors as the pipettes are not accurate to the hundredth of a millimetre. Also human error could have affected the method in terms of the making of hydrogen peroxide and the quality of the hydrogen peroxide. Also the variation of temperature with the surroundings, as the temperature fluctuates and could not be kept constant. Also the experiments and all the repeats could have been done on the same day and at the same time but this was not possible as the apparatus and time was limited. another way in which I could have improved the method was keeping the pH level constant. Every enzyme has its own range of pH in which it functions most efficiently. Most intracellular enzymes function best at or around neutral. Excessive acidity or alkalinity renders them inactive.
