Peroxidase Enzyme Lab

Helen Hills Per 5

                             Peroxidase Enzyme Lab

Question

How do abiotic or biotic factors influence the rates of enzymatic reactions (chemical reactions that are assisted by enzymes)?

Purpose

By doing this experiment we hope to find the effect that different pH levels have on the rate of the decomposition of the hydrogen peroxide. To do this we are going to use grass as our enzyme extract, hydrogen peroxide, and four solutions with different pH’s.

Hypothesis: By adding an acidic solution we believe the decomposition of the hydrogen peroxide will be accelerated.

Independent Variable: The independent variable is the pH caused by the acidic and basic solutions

Dependent Variable:  The dependent variable is the decomposition of the hydrogen peroxide

Controlled Variables: The controlled variable is the amount of the bindweed vine and hydrogen peroxide

Justification of hypothesis: Acidic solutions can accelerate decomposition so by adding an acidic solution the decomposition of the hydrogen peroxide will be increased

Materials :

• 5 grams of freshly picked grass
• Digital balance (scale)
• Mortar and pestle
• 12 mL Distilled water
• 3 100-liter plastic beakers
• 5 mL syringe
• 2 1 mL syringes
• 1.5 mL Hydrogen peroxide
• 1 Paper towel square (for filtration)
• 5 glass test tubes
• Test tube rack or holder
• Small plastic ruler
• Safety glasses

• .2 mL Hydrochloric acid solution pH 2-3
• .2 mL Hydrochloric acid  solution pH 3-4
• .2 mL Sodium hydroxide solution 10
• .2 mL Sodium hydroxide  pH 12
• pH test strips

Procedure:

We plan to mix hydrogen peroxide with the grass and then make separate mixtures with an acidic or basic solutions added to each. We then plan to take note of the changes of the decomposition of the hydrogen peroxide in each mixture  

Steps:

1. Measure out 5 grams of the grass
2. Measure out 10 mL of water
3. Use the mortar and pestle to mash the grass with the water
4. Filter the water and grass solution through a paper towel into a beaker
5. Pour 1.5 mL of the grass and water solution into 5 separate test tubes
6. Check pH of Hydrochloric acid and Sodium hydroxide
7. Label the tubes A, B, C, D, E
8. Measure out 1.5 mL of hydrogen peroxide
9. Out .3 mL of hydrogen peroxide in test tube A
10. Put .2 mL of water in test tube A
11. Use timer and ruler to check level at beginning, after 5 seconds, after ten seconds, and after 15 seconds
12. Put .3 mL of hydrogen peroxide in test tube B
13. Put .2 mL of Hydrochloric acid pH 2-3 in test tube B
14. Follow step 10 with test tube B
15. Put .3 mL of hydrogen peroxide in test tube C
16. Put .2 mL of Hydrochloric acid pH 3-4  in test tube C
17. Follow step 10 with test tube C
18. Put .3 mL of hydrogen peroxide in test tube D
19. Put .2 mL of Sodium hydroxide pH 10 in test tube D
20. Follow step 10 with test tube D
21. Put .3 mL of hydrogen peroxide in test tube E
22. Put .2 mL of Sodium hydroxide pH 12 in test tube E
23. Follow step 10 with test tube E
24. Compare results for each tube

Data and Results:

 

Conclusions:

The data shows in this experiment the control had a final measurement of 3.7 cm, Hydrochloric acid of pH 2-3 had the final measurement of 4.6 cm, and Hydrochloric acid 3-4 had the final measurement of 5 cm. Then surprisingly, the Sodium hydroxide of pH 10 had the final measurement of 5.5 cm and the Sodium hydroxide had the final measurement of 4.5 cm. From this data it can be concluded that the tubes with the pH 3-4 and pH 10 produced the greatest change.  This is a very surprising result considering that the enzymes we were told about had to be kept at a certain pH to work. The enzymes we learned about had to be in a certain pH to work correctly which is usually the pH of about 7 to 9. However I did some research and found out that unlike most other enzymes, plant-based enzymes can work in a wider range of different pH substances. In addition to this, they can work in a larger range of temperatures than animal enzymes can. This explains why the acidic and basic substances still reacted the way they did. In all of our trials the experimental substances rate of decomposition was more or equal to the control. This does not however explain why the more basic solutions still had faster rates. However in all of our trials this was consistent.    

We had multiple problems that arose with this experiment. When we first came up with the measurements for the amount of substance we should put in each test tube we overestimated. So, when my partner and I finally conducted the experiment, the substance bubbled over the sides. This actually occurred multiple times as we tried to find the correct measurements that would not cause the substance to react this way. The other issue we had was when we ran out of time and ended up using two different batches of bindweed for one experiment. This introduced a completely new variable. The reactions for the substances were very different because of this. Another problem we ran into was when we ran out of bindweed and had to use the grass as a substitute. When we did this, we had to change the measurements yet again to suit the needs of the different plant.

To improve this experiment, it would be a good idea to use a plant that is growing in really large quantities in the garden. We could use more of the grass like my partner and I did in our experiment. There was not enough bindweed for all students to have the correct amount that they needed for their experiments. I also think it would be beneficial to the students doing the experiments to do at least two trials with the same measurements. By did this we would be able to compare the results and notice any mistakes we made in the different trials.

 Now that the experiment is finished I would like to know why the more basic substances acted the way they did. The average pH needed for plants enzymes are 3 to 9. However, the sodium hydroxide solutions had the pH or 10 and 12. So if I were to do this experiment again I would like to find the answer to this problem. I would also like to see how the temperature affected the solutions.