Enzyme Lab

Enzymes

The Rate of Reaction on Liver, Apples, and Potatoes with Hydrogen Peroxide

AP Biology, Mod 5

Abstract:

The purpose of this lab was to test enzyme function in various environments. Substrate concentration, temperature, and pH all affect the chemical reaction. In this lab, the enzyme catalase was used to break down hydrogen peroxide into less toxic water and oxygen gas. Using quantitative as well as qualitative observation the concept that enzymes remain after a reaction was confirmed from the first test. After testing liver, apple, and potato it was concluded that liver contained the most catalase. The final test focused on the reaction rate of liver in varying pH solutions. The relationship between catalase reaction rate and pH was shown to be parabolic with a peak near neutral.

Introduction:

This lab covered the measuring of the effects of changes in temperature, pH, and enzyme concentration on reaction rates of an enzyme catalyzed reaction in a controlled experiment. The questions of how environmental factors affect the rate of enzyme-catalyzed reactions were answered in this lab. The reaction rates of enzymes were very much affected by changes in temperature, pH and enzyme concentration. The enzyme studied in this lab was catalase. Catalase breaks down hydrogen peroxide, which is toxic, into 2 safe substances- water and oxygen, by speeding up a reaction. Enzymes such as catalase are vital to our body, because if toxic substances such hydrogen peroxide were not broken down into harmless substances in our body, then they would poison our cells. The reaction that takes places is in this form: 2H2O2 ----> 2H2O + O2

Methods:

This study was conducted at New Tech High @ Coppell under the facilitation of Mrs. Wootton on October, 8 2015. Throughout the three parts of the lab, the ability for enzymes to break down was studied. In Part A, we used 3 ml of 3% Hydrogen Peroxide on a piece of liver to observe the rate of reaction. Once this was done, we took the leftover liquids and used it on a new piece of meat to see if the enzyme was reuseable. In Part B, we tested, observed, and recorded the rate of reaction with Hydrogen Peroxide on three substances: apple, liver, and potato. In Part C, we altered the pH of the solution by adding drops of diluted Hydrochloric Acid to see if it had an affect on the rate of reaction in catalyses on pieces of liver.

Results:

When the substrate of hydrogen peroxide was added to the substances each performed a vastly different reaction. After dropping the hydrogen peroxide on the apple samples there was no reaction indicated therefore receiving a rating of 0. Once the same amount of the substrate was added to the potato there was a slight fizzy and bubbly reaction thus earning the rating of 2. The liver catalase was then tested and resulted in the largest reaction that was given a rating of 5 due to the speed and magnitude. After testing each substance the group then began to look into optimal conditions of pH for the reactions. After adding hydrochloric acid onto the liver the reaction rate seemed to diminish as the acidity increased.

Discussion:

Catalase: Liver

Substrate: Hydrogen Peroxide

Looking at our data for the first experiment, we can infer that the liver contains the catalase enzyme while the hydrogen peroxide is the substrate. This is true because in the reaction, the hydrogen peroxide is observed to have gone through a chemical change; turning into water molecules and dioxide molecules, whereas the liver stayed the same. Because the substrate already went through the chemical reaction, it could not go through another one with new catalase, but the old catalase still had functional enzymes and could therefore be reused. The reaction was very apparent and quick, which makes sense considering the liver’s function in an organism is to break down and purify cells.

In the second part of the experiment, the intensity of the reaction in ascending order was apple, potato, and liver. The apple sample is simply carbohydrates meant as food for the apple seed and will have no enzymes in it, thus no reaction was observed. The potato will have a semi-intense reaction because only a small concentration of the sample of potato is enzymes whereas the rest is starch and organic compounds. The liver will have a large reaction because the majority of liver is proteins and enzymes which break down the Hydrogen Peroxide.

In the third experiment, it was inferred that as the acidity increased in the substrate, the rate of reaction decreased. Our data shows a linear trend, however, research shows that the trend is in fact a parabola opening downwards with a maximum at a pH of 5, the acidity of Hydrogen Peroxide alone. Because we were only able to stimulate an environment of a lower pH, we were only able to get 1 direction of slope, showing linear results. This shows that enzymes only work in a certain pH level. If it’s too high or too low, it will reduce the efficiency and slow down the rate of the reactions.

Conclusion:

Through our experimentation the reaction between the enzyme catalase and hydrogen peroxide was tested. Repeating the reaction with various materials allowed for the concentration of catalase to be inferred. Using liver as our control, we changed the pH of the solution in each trial to test the reaction rate as the acidity increased. We concluded that as the pH of a solution increased the reaction rate increased inversely until a pH of about 5. The error within our experiment only altered the specific pH but the overall result of the last test remains true.