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The Effect Of pH On Enzyme Action

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Enzymes are proteins that act as catalysts within living cells. Catalysts increase the rate at which chemical reactions occur without being consumed or permanently altered themselves by lowering their activation energy (Christensen, 2018). Every enzyme has a region called active site, where enzymes are binds to a substrate to create another enzyme and carries a reaction. Enzyme is important because it’s a metabolic pathway in the body like respiration, building muscle, destroying toxins, and breaking down food particles during digestion (Roland, 2018). Without enzymes, these reactions would take place too slowly to keep living organisms alive. Additionally, factors like the concentration of the enzyme, temperature, pH, and the presence of inhibitors can affect the overall performance of an enzyme.

Catalase is a very common enzyme that is present in almost all organisms that are exposed to oxygen. The purpose of catalase in living cells is to protect them from oxidative damage (Augustyn, 2019). As catalase can

catalyse the decomposition of harmful superoxide radicals into oxygen and water. Scientifically, each and every enzyme is characterized by an optimum PH. At this specific pH level, a particular enzyme catalyses the reaction at the fastest rate. Any change in this pH significantly affects the enzyme activity and/or the rate of reaction (Gillespie, 2018). In human, catalase works only between pH 7 and pH 11. If the pH level is lower than 7 or higher than 11, the enzyme becomes denatured and loses its structure (Gillespie, 2018).

The purpose of this experiment was to investigate if higher PH range would increase the active rate of enzyme catalse in hydrogen peroxide, as measured by the amount of oxygen released. In the experiment, different PH range of 4,7, 10 will be tested on potato cores in hydrogen peroxide (H2O2). It was hypothesised that higher PH level will cause greater reaction on the enzyme activity mixed with H2O2. This is because catalase works best at high levels of substrate concentration and PH levels, therefore the higher the concentrations of each variable, the more oxygen will be produced when molecules of hydrogen peroxide are free (Brooker et al., 2008).

The effect of surface area on the enzyme reaction

The original experiment was to determine the relationship between surface area and the rate of oxygen produced when different sized potato cores were placed in Hydrogen Peroxide over one minute. It was hypothesised that the potato that has been cut into the smallest pieces will have the largest surface area and cause a greater reaction (produce more oxygen). This statement was proven truthful after the experiment. In the result table, it was evident that the potatoes with the largest surface area (grind ones) had the greatest amount of oxygen produced at an average of 6.1cm. Follow by the quarters (3.5cm), the thirds (3.05cm) and lastly the half (3cm). The is because potato core with the large surface area will contain more catalase molecules coming in contact with the reacting substrate and hydrogen peroxide. Which means if more of an enzyme is exposed (meaning larger surface area) a greater number of active sites will be available to react with the hydrogen peroxide. Thus, produce more oxygen.

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In the original experiment, numerous amounts of limitation and error was identified. Those include, the size of the potato cores was not even, the way that liquid and the level of reaction was not measured accurately and more. These errors had a significant impact on the rate of reaction and the reliability of the result. In order to ensure more precise and sufficient data was collected, the original experiment was changed to keep all size of the potato cores the same but changing the range of PH. As all potato cores are the same, therefore it will contain the same amount of catalase. Which minuses the impact to the rate of reaction and the results can be compared more efficiently. Furthermore, more reliable data was determined and improved by using correct measuring technique and equipment. Overall, most of the limitation and error in the original experiment has been minimised and fixed.


  • Four trials of each PH level (4,7,10) will be tested to ensure that the data result will be more reliable and sufficient, so more accurate mean and standard deviation can be calculated.
  • A more scientific way of measuring the liquid was discovered and used. Which was placing the test tube on the table and measure the liquid from eye level using a ruler.
  • In the previous experiment, the height of the potato cores was taller than the height of the amount of hydrogen peroxide. This has indicated an error that only some parts of the potatoes were in the process of reaction. In order to solve this problem and improve the reliability of the result, the amount of chemicals (hydrogen peroxide and PH) was increased to ensure every part of the potatoes could react with the chemicals.


The graphs above has indicated a relationship between the PH range and the enzyme activity. It was shown that higher PH level will cause a greater impact on the enzyme activity. This is because as the PH level increase there will be a higher concentration of enzyme , which means there is a greater chance of an effective collision between the enzyme, hydrogen peroxide and molecules. In both graphs, the maximum rate of reaction occurred in PH 10 at 9.1cm and the minimum rate had occurred in PH 4 at 7.4cm. When higher PH level react with enzyme, it will cause a greater amount of oxygen released. For example, the amount of oxygen increased averagely 14% in PH 10, then 12.1% in PH 7 and lastly 12.8% in PH 4. Aside from that, the height of oxygen had only increased 0.5 cm between PH 4 and 7 but 0.85cm between PH 7 and 10. Which evident that PH 10 is the optimal PH level for enzyme as it has the maximum amount of oxygen produced, meaning higher enzyme activity. Additionally, the standard deviation error bar does not overlap each other in either the line or bar graph. This specified the fact that there may be a significant difference of PH range on enzyme activity. Overall, trend and pattern shown in both graphs was expected.


After the experiment, all the data and results were carefully examined to ensure reliability and validity. Numerous amounts of factors that result in uncertainty or limitation were observed. During the experimental process, the temperature is considered to be another factor that could control and affect the enzyme catalase. High or low temperature can change the shape of the active site and cause a significant impact on enzyme activity. This will then lead to a process called denaturation, where enzyme catalase is dissolved. This uncertainty could reduce the validity of the results as the temperature could possibly be the major factor that has a greater impact on enzyme activity, instead of the PH range.

However, when examining the graphs, it was obvious that the standard deviation error bar is small. This suggests that the mean value was represented accurately in the data set, which leads to proving that the results are reliable. Additionally, this could be explained by the number of repeats that was done to ensure validity. When comparing the data from four trials for each PH, it was clear that the values for all PH range were very close together. Which evident that there is not an outlier or anomaly shown in the result table.

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The Effect Of pH On Enzyme Action. (2022, February 17). Edubirdie. Retrieved December 5, 2022, from
“The Effect Of pH On Enzyme Action.” Edubirdie, 17 Feb. 2022,
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