What factors will affect the rate of reaction of a controlled enzyme experiment?

Diagram

Apparatus

• Boiling tube
• Water bath
• Pipette
• Standard lab thermometer
• Stop clock
• Water baths at several temperatures
• Pepsin
• Hydrochloric acid
• Egg white

Method

• Protein, in the form of egg white will be placed into a boiling tube.
• The enzyme pepsin mixed with hydrochloric acid will then be added to the boiling tube.
• The boiling tube will then be placed in a water bath.
• A black cross will be placed behind the boiling tube and the time taken for this to be visible through the boiling tube will be recorded.
• The exact same procedure will be repeated but the boiling tube will be placed in water baths of different temperatures.

During my experiment I will measure:

• The amount of egg white used (3cm³)
• The amount of pepsin added (2cm³)
• The amount of hydrochloric acid mixed with the pepsin (1cm³)
• The time taken for the substances in the boiling tube to go clear.
• The temperature of each water bath using a standard lab thermometer ranging from -10ºC to 120ºC, which will be placed in the water bath.

I will ensure accuracy by rounding measurements to the nearest 0.5ºC.

I will vary the temperature of the water baths in the range of 0ºC to 80ºC, and there will be five readings within this range, which will be approximately 0ºC, 20ºC, 40ºC, 60ºC, and 80ºC.

The experiment will be repeated at least twice to ensure accuracy and to obtain an average result.

I will ensure the experiment is a fair test by:

• Keeping the amount of egg white used the same throughout the experiment.
• Ensuring the same amount of pepsin and hydrochloric acid is used throughout the experiment.
• Carrying out the experiment on the same day as the same equipment will need to be used.
• Ensuring I record the time from when the black cross first becomes visible each time I do the experiment.

I will use safety goggles as a safety precaution.  

Results

                         

                Temperature of                 Time taken for

                water bath (ºC)              black cross to

                                              become visible

                                                          (mins:secs)

Secondary sources of information I used was Heinemann Co-ordinated Science by Richard Fosberry and Jean McLean.

Jenny Haselden 11V1/11G1 – Biology AT1 Section B

Results

Experiment 1

Experiment 2

As it is difficult to obtain an average time, I calculated a total time for the two reactions:

These results helped me to come up with the following conclusion:

Conclusion

An increase in the temperature of the substances in the reaction, causes the rate of reaction to increase also, but only up to 34ºC. After this, the rate of reaction decreases as the temperature increases.

        This proves that my prediction was correct, based on the following scientific knowledge:

        Collisions between particles inside different substances are the reason a reaction takes place. The more collisions occurring between the particles, the greater the rate of reaction is. To enable more collisions to take place, the particles need more energy, and one way of gaining this is to heat them up.

In my experiment, the particles in the substances were gaining more energy as the temperature was increasing, which is why the rate of reaction increased.

However, enzymes are specific which means they only react with certain substrates. Too much heat causes the enzymes to become denatured, which means they change their shape and cannot react with their substrate.

In my experiment, the rates of reaction began to decrease after 34ºC because the heat caused the enzyme to denature and therefore the protease could not react with the protein.

Section C

Evaluation

        

        In my original plan, I stated that I would carry out my experiment at five different temperatures; 0ºC, 20ºC, 40ºC, 60ºC and 80ºC. In my real experiment, I changed the number of different temperatures to six, and this was to extend my investigation. I also changed the actual temperatures of the experiment to 5ºC, 12ºC, 34ºC, 50ºC, 69ºC, and 80ºC. This was because it was difficult to reach exact temperatures.

        I think that my results were fairly accurate, given that they follow my scientific theory.

        However, from my graph I can see that the results for 50ºC and 69ºC are slightly anomalous. They still follow my theory, but I think as they were the last two reactions to take place, the protein had been left to stand longer and was no longer fresh, and this had affected the results.

        I do not think that my method was the most suitable as it was very difficult to obtain accurate results, ie it was difficult to assume when the reaction had taken place just by looking at how clear the solution was. Problems arose as many times the black cross being used could already be seen through the solution at the beginning of the reaction, even if the solution wasn’t completely clear.

        If I was to repeat this experiment again, I could use the clear enzyme as a control to compare it with the reacted solution instead of the black cross method, to provide more accurate results.

        I would also use the egg white straight away and not let it stand around for as long, as this may affect the results.

        I would also keep the reactants in the water bath as the reaction is taking place, as allowing it to cool down may have affected the results.

        

        To extend my investigation I would try this experiment with different substrates, ie starch or carbohydrates and also with different enzymes to see if the same theory applies for them.

        I could also carry out the experiment at different temperatures to further extend my results and I could carry it out more times to ensure reliable results.