From this experiment, we learned that the rate of increase in enzyme activity was proportional to the increase in concentration of the substrate. As we added in more substrate, the rate of reaction steadily increased as more of the molecules of the substrate would diffuse into and bind with the active sites of the enzyme, catalase, which were being used and more oxygen was produced at a given time. However, the rate of increase slowed down as reflected in the graph which levelled off after the point when l% concentration H₂O₂ had been added. The reason for this result is that enzymes are not just passive surfaces on which reactions take place. Rather, they are complex molecular machines which operate their catalytic functions through a great diversity of chemical mechanisms. According to Michaelis-Menten Kinetics, enzyme-substrate reactions are actually comprised of two reactions, the first is when the substrate forms a complex with the enzyme and then in the second, the complex decomposes to product and enzyme.

      Enzyme + Substrate <--> Complex --> Product + Enzyme

Based on this model, when the substrate concentration becomes high enough to entirely convert all of the enzyme to the complex form, the second step of the reaction becomes insensitive to further increases in substrate concentration. Consequently, the increase in rate of enzyme activities did not increase as fast as the increase in the concentration of the substrate as shown in the graph which began to level off after the point of l% H₂O₂.

From the experiment on enzyme concentration, we learned that the rate of reaction increased with the increase in concentration of the enzyme. With higher concentrations of enzyme, there are more active sites of the enzyme to be used and there is a greater chance of an effective collision between the enzyme and hydrogen peroxide molecule. Any increase in enzyme concentration means an increase in the binding sites. Enzymes speed up reactions by bringing the reactants closer to each other and by placing them in the optimal 3-dimensional arrangement so that reactions may occur. Upon binding of the substrate to an enzyme, the structure of the protein around the active site undergoes a change so as to orient the reactants and help in the formation of a product. The final product, which is then released from the enzyme, will return to its original configuration. The rate of increase in activities is proportional to the increase in concentration of the enzyme until the solution becomes saturated with enzyme. Usually, the concentration of enzyme is very small compared to that of the substrate. Therefore, enzyme activities increase with increases in enzyme concentration.

The results of the experiment on how different pH affect the activities of the enzyme catalase showed that enzyme’s activities increased as pH increased from 5 to 9 with an optimum pH of 7. At extremes of pH, low pH values below 4 and pH above l0, no activities of the enzyme were shown as the protein might have denatured or changed structure. The reason for this is that pH can affect the ionization of the acidic or basic amino acids. Acidic amino acids have in their side chains carboxyl functional group. Basic amino acids have amine functional group in their side chains. These groups readily gain or lose H+ ions. The change in ionization of the amino acids in a protein is to alter the ionic bonds that help to determine the 3-D shape in protein. This leads to an altered protein recognition which renders the enzyme inactive. In addition to changing the shape of the protein, a change in the pH also changes the charge properties of the substrate so that either the substrate cannot bind to the active site or it cannot undergo catalysis. Finally, enzymes have a pH optimum and different enzymes may have very different optimum. Some enzymes, for example, pepsin may have a very low pH while other enzymes like carbon anhydrase works best at a neutral pH. Putting the enzyme catalase in extremes of pH, for example, pH 2 to 4 and above l0 which are outside its optimum range would lead to the unfolding of the peptide bonds and the structure of the enzyme. This change in the structure of the enzyme would affect its lock and key relationship with its substrate and thus affects its ability to recognize a substrate and hence loses its enzymatic functions.

As reflected by the results of the experiment, enzyme activities increase from 5ºC onwards to about 40°C with the maximum level of activities at the temperature 25ºC (optimum temperature). The lowest rate of enzyme activity was 50 °C. Similarly, no enzyme activities were recorded at the temperature 0ºC. The reason for this is that for chemical reactions to occur, energy must be added to the reactants to overcome the energy barrier. This added energy is called activation energy, without which reaction may not even occur. This explains why there are no activities recorded at 0°C as the molecules of the enzyme do not have the energy required to begin the reaction. Chemical reactions speed up as the temperature is raised as more of the reacting molecules have the kinetic energy required to undergo the reaction. Enzyme catalyzed reactions also tend to go faster with increasing temperature until a temperature optimum is reached. At higher temperatures, particles have more energy and are likely to be more successful in colliding with each other and there are more collisions per second. The rate increases as the temperature increases, until the temperature reaches about 25° C – the optimum temperature. As the temperature of the system is increased, the internal energy of the molecules in the system also increases. The internal energy of the molecules may include the translational energy, vibrational energy and rotational energy of the molecules, the energy involved in the chemical bonding of the molecules as well as the energy involved in the non-bonding interactions. If the temperature is raised further after the optimum is reached, the kinetic energy of the enzyme is so great that the weak bonds which hold the molecule into its specific shape are broken. The increase in molecular collisions and vibrations at high temperatures is so great that the shape of the active sites is permanently changed. The enzyme is said to be denatured because it cannot form an enzyme substrate complex and its activities are irreversibly changed. So while the rate of reaction of chemical reactions goes faster at higher temperatures, the shape of the enzyme molecule changes as well so that it is less and less efficient as a catalyst as the change in conformation of the catalyst results in less efficient binding of the substrate. Therefore, the rate of increase in activity increases with temperature up to a point and then abruptly decreases. In general, temperatures above 40-50 ºC denature many enzymes. As evident in the results of the experiment, the result showed a marked decline in the level of enzyme activity when the temperature reaches 30°C. Above 50°C, no activities were recorded as enzymes, being proteins, are unstable and undergo rapid denaturations above the critical temperature of 50°C and consequently lose their activities as catalysts.