Enzymes Affecting Enzyme Activity

Ashlyn Fairchild


A lot of organisms decompose hydrogen peroxide (H2O2) using enzymes. Enzymes reaction rate can be affected by various conditions. By changing temperature or the pH of the enzyme's habitat, we can deduce which conditions create the optimum conditions for enzymes to work, creating a maximum rate of reaction.

Research Question

Does the pH affect enzyme activity?


In the experiment, we started by putting a mixture of 3 ml of 3% hydrogen peroxide and 3 ml of a liquid of a predetermined pH (4, 7, or 10). When ready, we used a pipette to put 2 drops of the yeast solution into the test tube containing the hydrogen peroxide and quickly capped the tube with the pressure sensor to gather data on the logger pro. We repeated this for all different levels of pH. We made sure to use safety goggles.

Independent Variable- different pH's in solution (4,7,10)

Dependent Variable- Pressure (kPa), reaction rate

Constants- amount of drops of yeast solution, temperature, amount of peroxide and pH in solution


Explanatory: There is a optimum pH which will produce the max rate of reaction.

Prediction: If the pH is too high or too low, then the rate of reaction will decrease.

Null: There is no affect on the rate of reaction because the optimal temperature stays the same despite the pH, so since the temperature (which affects enzyme activity )is staying the same, so should the reaction rate.

Alternative: There is an affect in the reaction rate because the pH can change specific bond interactions between the substrate and the enzyme which would affect the enzyme's ability to work at its maximum rate.

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Big image


The solution with a pH of 7 provides the optimal conditions for the enzyme to work at its maximum rate.


Line graph- All the test tubes start at relatively the same pressure (pH 4- 100.86 kPa; pH 7- 100.69; pH 10- 101.09) . As time goes on, the solutions with pH 7 and 10 continue to have about the same rate of reaction compared to pH 4. They end with about the same pressure. The pH 7 solution has a slightly higher pressure (112.41 kPa) than pH 10 (112.35 kPa). The pH 4 has a smaller pressure change than the other two solutions, ending with a pressure of 104.54 kPa.

Bar graph- The solution with pH 4 has an average rate of reaction is about 0.01482 kPa/s. The solution with pH 7 has an average rate of reaction is about 0.06741 kPa/s. The solution with pH 10 has an average rate of reaction is about 0.0629 kPa/s. The solution with pH 7 has the highest rate of reaction with the solution with a pH of 10 coming in 2nd and the solution with pH 4 with the slowest reaction rate.


The experiment measured if there is an optimum pH which will make the enzyme rate of reaction work at its max.

The solution with a pH of 7 was the optimal pH to help the enzyme work at its maximum rate because it had the highest average rate of reaction (0.067412 kPa/s) compared the solution with a a pH of 4 (0.01482 kPa/s) and 10 (0.0629 kPa/s). The solution with a pH of 7 had the highest rate of reaction because it had the largest change in pressure over time. The bigger the change in pressure, the more chemical reactions are occurring between the enzyme and substrates because the enzyme (catalase in yeast) is breaking down the substrate (hydrogen peroxide) into water molecules and oxygen. A build up of oxygen leads to an increase in pressure; therefore, the more reactions, the more oxygen products, the higher the pressure, the higher the rate of reaction. With the other solutions of pH, the pH was more acidic or basic which hindered the bond interactions between the enzyme and substrate, so less reactions were able to occur, making less oxygen, having a lower pressure, and having a slower reaction rate.

Errors that could have occurred- The person holding the cap could have accidentally released some air during data collection by not keeping the cap completely secure, changing the pressure reading. The person holding the cap could have not put the cap on the tube after the yeast solution was added in the same amount of time each round, letting more air escape and getting a different pressure reading. The amount of yeast solution could have been different. The amount of drops of yeast solution was controlled, but one drop could have been larger than the others.

How experiment can be improved- Conduct more trials to ensure a better collection of data.