RP1: Investigating the effect of a named variable on the rate of an enzyme controlled reaction Flashcards
We are investigating the effect of substrate concentration on the rate of catalase activity. What is catalase as an enzyme and what does it do
Catalase breaks down hydrogen peroxide[Substrate] into water and oxygen
Why do we add washing up liquid/detergent to the reaction mixture/substrate
Because the detergent will trap the oxygen released in the foam. We can measure the height of the foam produced in a given time. This gives a measure of the rate of enzyme activity.
What is the procedure for this experiment
1: label for test tubes with a different buffered concentration of hydrogen peroxide. And pipette 2 cm³ of the appropriate concentration into each tube
2: add two drops of detergent
3: now place all four test tubes in a water bath maintained at 40°C and warm up for three minutes for equilibration
4: Cut 4 cylinders of potato
5: place a potato cylinder into each test tube for three minutes
6: Measure the height of the foam produced after three minutes
7: Work out the mean height and plot a graph
Explain why the different hydrogen peroxide concentrations were prepared using a buffer rather than distilled water
A buffer solution controls the pH and keeps it at a constant, the pH could affect enzyme activity so buffet is needed in this experiment.
Describe three limitations in this investigation
The catalase concentration/the enzyme concentration may not have been the same in each piece of potato wedge.
Some of the oxygen could escape and not be trapped in the detergent solution
What is the independent variable and how do you know
The independent variable is the substrate concentration/hydrogen peroxide concentration as this is what is changed in the experiment
What is the dependent variable and how do you know
The dependent variable is the height of the foam in three minutes as it is the variable we measure
What are the controlled variables and how are they controlled
The enzyme conc in the potato.
The temperature
The volume of the substrate
The number of drops of detergent
The same size volumes for each cylinder
temperature at 40°C

What would be a suitable control experiment and what will it show
A controlled experiment would show that it is only that enzyme catalase that is causing the reaction to occur. We could have repeated the experiment with cooked or boiled enzyme as this will denature the enzyme so no oxygen/foam is produced.
Experiments are usually repeated why is this important
To make sure that anomalous results are discarded. you could take an average of the results and this would provide a more accurate results. So we can identify a pattern or a trend among the results.
why is it important to equilibrate The test tubes for three minutes in the water bath
So that the temperature of the substrate and enzyme is at its optimum before starting the experiment [40°C]
Give two reasons why the catalase solution was prepared using a buffer solution rather than water
Because the buffer solution has a pH to remain constant for example the pH in this experiment remained at pH seven. If the buffer solution was replaced with water the pH could change and this could affect the enzyme by denaturing it
What trend does an increasing concentration of hydrogen peroxide show
The higher the hydrogen peroxide concentration, the more oxygen produced therefore the more bubbles produced.
what is a photometer
A piece of equipment that measures light for example in a reaction that is going from colourless to a cloudy solution you could say the endpoint is when no more light can pass through the solution.
