Factors Affecting Enzyme Activity

By: Anu Singh, period 4, Ms. Ferguson, Allen High School


Enzymes are catalysts that speed up chemical reactions without being destroyed and can be used over and over again. They reduce activation energy and substrates bind to their active sites and are broken apart. Both temperature and pH have effects on enzyme activity. H2O2 or hydrogen peroxide is toxic to organisms so they enzymatically destroy it using catalase.


In our experiment, we wanted to measure the effect of pH on enzyme activity.

Effect of pH on enzyme activity

Research Question

What is the effect of pH on enzyme activity?


Explanatory Hypothesis: I hypothesize that on average, enzyme activity will increase when it is at its optimal pH of 7.

Prediction: If an enzyme reaches its optimal pH of 7, then it will have its optimal activity since it will be enough to lower activation energy, but not too much to denature it.

Null Hypothesis: pH has no effect on enzyme activity.

Alternative Hypothesis: Optimal pH of 7 determines the likelihood of increased enzyme activity.


When an enzyme is at its optimal pH of 7, it will have the most activity.


Independent Variable: pH of buffer

Dependent Variable: Pressure

Constant: Amount of H2O2


amount of enzyme solution



LabQuest App

Vernier Gas Pressure Sensor

Rubber-stopper assembly

10mL graduated cylinder

250mL of water


Enzyme Suspension

4 18x150mm test tubes

test tube rack

4 disposable pipettes

Logger Pro

pH buffer


  1. Put 3 clean test tubes in a rack and label them pH4, pH7, and pH10.
  2. Add 3 mL of 3% H2O2 and 3mL of each pH buffer to each test tube
  3. In each tube add 2 drops of the enzyme solution
  4. Mix the substances in the tube and collect the pressure readings
  5. Remove and clean the tube
  6. Store Data
  7. Transfer data to excel and create and analyze data
  8. Repeat these steps for each pH
  9. Graph all three runs on one graph


Big image


When the buffer of pH 10 was added, the enzyme reached its optimal activity in the shortest time of 25 seconds. It took a little longer for pH 4 to reach its optimal activity which was 40 seconds. For pH 7, it was 100 seconds. After that all the graphs leveled off.


In our experiment, we recorded what effect different pH had on enzyme activity. My claim that when an enzyme is at its optimal pH of 7 it will have the most activity is not supported by my data. It appears that the enzyme's optimal pH is 10, which is basic. This is because it reached its transition state the quickest which is 25 seconds which is less than those of pH 7 and 4 which were 100 and 40 seconds respectively. Its rate of reaction is also the largest since it is .17 kPa/s which is larger than pH4's which is -.013 and pH7's which was .064. The enzyme reached its most activity at its optimal pH of 10 because it has more OH- concentration than H+ and since these ions interfere with hydrogen and ionic bonds that hold enzymes together, a basic solution will change the shape of the Active site of the enzyme so that it is more complementary to the substrate.

Some errors that may have occurred were that the amount of pH added was not the precise amount, and the tubes may not have been properly cleaned, so they might have contaminated the hydrogen peroxide. To improve the experiment, we could do multiple trials of each pH to get more reliable data.

In the future, we can also test more pH values to find a more specific optimum pH.


Enzyme cycle picture: slideshare.net