Effect of Substrate Concentration on Rate of Reaction

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Investigation

Aim:
The aim of the investigation was to investigate the effect of substrate concentration Hydrogen Peroxide H O (in %) on the rate of reaction of the enzyme catalase (in 1/mean time). Prediction:
As the substrate concentration (hydrogen peroxide) in % increases the rate of reaction in 1/mean rate increases until the solution becomes saturated with the substrate hydrogen peroxide. When this saturation point is reached, then adding extra substrate will make no difference. The rate steadily increases when more substrate is added because more of the active sites of the enzyme are being used due to more collisions between the substrate and enzyme because there are more molecules of hydrogen peroxide, so there will be an increase in enzyme-substrate complexes formed which results in more reactions so the required amount of oxygen is made more quickly. Once the amount of substrate molecules added exceeds the number of active sites available then the rate of reaction will no longer increase, as the maximum number of reactions has already taken place. This means that any extra substrate molecules will not to bind to the active site to form E-S complexes as there are limited active sites, in which by this point all the active sites would have been used up.

Experimental Design –
Independent Variable:
The independent variable, is the variable that is changed, this was the substrate concentration in potato discs. The dilutions of Hydrogen Peroxide were 0.2%, 0.4%, 0.8%, 1.2%, 1.6% and 2.0%. Dependent Variable:

The dependent variable is the variable that is measured, in this experiment the dependent variable was time taken for disc to reach the surface. Rate = 1/mean time. Controlled Variables:
The controlled variables were volume of hydrogen peroxide which was 10cm³, concentration of hydrogen peroxide of 2% stock concentration. Also same size discs of the potato which were 2mm. The enzyme concentration has to be kept constant because if more enzymes are present, more active sites will be available for the substrate to combine with it. Same source of enzyme, the potato must be cut out from the same one because there are different amount of catalase present in different sources. Repeatability:

The more repeatable the experiment is the less variation there is and the greater confidence in the mean. Every concentration of the hydrogen peroxide (Substrate) was repeated at least 4 times, whereas some of the concentrations were repeated more times. For example concentration 0.8% and 1.2% were both repeated 13 times. A mean was calculated for each hydrogen peroxide concentration (substrate), which made the results more reliable. Having more repeats, decreases the variance in results therefore making them more reliable. Control Experiment:

The control experiment is using a denatured enzyme by boiling it. This would then be compared to the standard experiment above with an enzyme and different substrate concentrations. For this control experiment, the independent variable would remain the same which is the substrate concentrations. So in this experiment, we would investigate the effect of substrate concentrations on a denature enzyme. The controlled variables would remain the same, so this means that the volume of hydrogen peroxide which was 10cm³ and concentration of hydrogen peroxide of 2% stock concentration would be kept constant. Also same size discs of the potato which were 2mm would stay the same. Safety Risk Assessment:

The major hazard was spilling the Hydrogen Peroxide, because it is irritant. This means when inhaling it can damage lungs and throat causing shortness of breath and coughing. It can burn the eyes and skin and possibly cause eye g. There in order to prevent the spillage of hydrogen peroxide wear a lab coat to avoid any going on the skin or clothes. Wear safety goggles to prevent any contact with the eyes. Furthermore, wear gloves so that no hydrogen peroxide spills on your hands....
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