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Summative Practical 1

Guney Dogan


      Enzymes are very important molecules found in every cell. Enzymes act as catalysts to increase the speed or rate (successful reactions per time frame) at which biological reactions take place inside living organisms.

       Each enzyme has a different job and many enzymes work together to keep an organism functioning properly. In the liver, for example, there are several enzymes that break down certain toxic or poisonous compounds by removing hydrogen atoms from the poisons and transferring them to oxygen molecules. This detoxifies the poison but it creates a new compound, hydrogen peroxide (H2O2) that is very active and can be

harmful to the organism. Fortunately, there is another enzyme in the liver that helps break down the peroxide into water and oxygen. This enzyme is known as catalase. The catalase enzyme reduces the substrate, hydrogen peroxide, to water and oxygen by the following decomposition reaction.

                                                           2H2O2 -> 2H2O + O2

      Like all enzymes, catalase increases the rate of the reaction, but does not itself get used up in the reaction. Also like other enzymes, catalase has an optimum environment in which it functions best. Human enzymes, such as catalase, typically work best at normal body temperature (around 37°C) and when the pH is 7.3 7.4. If the environmental conditions are outside the optimum range, the catalase will lose its ability to catalyse the decomposition of hydrogen peroxide reaction effectively, or may be permanently denatured.

Aim:The purpose of the activity is to explore some of the factors that influence the rate of enzyme activity in a functioning organism.

Hypothesis: Read the method and write an appropriate hypothesis for this experiment. Try to write a single hypothesis to generalise the effect of each of the variables tested on the rate of hydrogen peroxide decomposition.

Materials and equipment (per group): See Handout

Safety: List 3 safety steps taken and why they were required!

Procedure: See Handout

Results: Fill in the table provided and write a brief summary of the key features of your results, but do not try to explain them yet.

Analysis and discussion:

1. Was this a controlled experiment? If yes, which of the tests performed is the control group? If not, describe an appropriate control group.

2. Explain what the differences in the results in Part A and Part B indicate about the function of enzymes.

3. Explain the effect of decreasing the pH (adding HCl) on the rate of reaction.

4. Explain the effect of increasing the pH (adding NaOH) on the rate of reaction.

5. Explain the effect of cooling the catalase on the rate of reaction.

6. Explain the effect of boiling the catalase on the rate of reaction.

7. Outline at least three safety precautions you followed to make your experiment safe and explain why they are relevant to this experiment.

8. Outline at least one improvement to the experimental design or procedure for this activity. What could you have done to improve the quality of your results?

9. Outline at least one recommendation for further research related to the function of enzymes. What would you do next?

Conclusion: Summarise your findings. (Remember to refer to your results!)

References: If needed.