LAB: Factors Affecting Enzyme Activity
Living cells use catalysts which are complex proteins. These catalysts, found in the body, are called
enzymes. Enzymes change the rate of a chemical reaction without being consumed by the reaction. They
lower activation energy and allow the transition state to be reached at lower temperatures and faster
speeds.
In a mammalian liver, hydrogen peroxide (H2O2) is produced as a result of processing digested food.
However, H2O2 is poisonous and therefore, the body must get rid of it so that it will not build up in large
concentrations. The body does this by using a catabolic reaction involving an enzyme called catalase.
Nearly all organisms produce the an enzyme to break down H2O2, which breaks down hydrogen peroxide
as it is formed. Potatoes are a good source for the plant source of catalase, called peroxidise.
As conditions change in our body and in plants, so does the speed and effectiveness of the reaction. In this
investigation, you will design a procedure and, with my approval, carry out experiments to test the effects
of temperature, pH, or concentration on peroxidise activity. There will be 4 groups, each group will test
one variable and you will share your results.
The Essential Question: How effectively do the enzymes peroxidase and catalase work at different
temperatures, pH values, and concentrations?
The Players:
(1) Peroxidase (enzyme)
 Potatoes are a source of peroxidase
(2) Catalase (enzyme)
 Liver extract is a source of catalase
(3) Hydrogen Peroxide (substrate)
Both Catalase and Peroxidase speed up the breakdown of hydrogen peroxide into water.
2H2O2
Catalase/Peroxidase
2H2O + O2
This reaction is detected by observing the oxygen bubbles generated.
The Factors: Temperature, pH, enzyme concentration, substrate concentration
Materials:
Catalase (liver extract)
Peroxidase (potato) (peeled, raw)
hydrogen peroxide 3% solution
hydrogen peroxide 1.5% solution
hydrogen peroxide 0.75% solution
hydrogen peroxide 0.5% solution
vials/test tubes, rack, tape
water baths
distilled water
 ice packs/ice
forceps/cruciable tongs
stopwatch/timer
thermometer
hot plate
Hydrochloric Acid (0.1 mol/L)
 Sodium Hydroxide (0.1 mol/L)
 Medicine droppers
filter paper discs (made with hole
puncher)
litmus paper – Anything else????
REMINDER – You will be working with Hydrogen Peroxide, which can be a dangerous acid. Use extreme
caution and WEAR GOGGLES AT ALL TIMES!!!
Part 1: Pre – Lab:
Plan it!
In your groups, you must create your own experimental design using only the materials given.
Complete the following:
1) Chose the specific enzyme you wish to work with
2) Chose the factor you wish to manipulate (consider both low and high temperature, pH values,
enzyme concentration and substrate concentration)
3) Make a hypothesis about how you think your factor will affect the rate at which the enzyme will
break down hydrogen peroxide.
4) Examine materials.
5) Chose the materials and methods that you will use to implement your experience and to record
and display your observations
6) Design a control to test variable
7) Submit experiment design for approval
Pre-Lab Questions (Must submit with experiment design):
1) How will you determine enzyme activity?
2) How will you measure amount of 02 produced?
3) How many trials will you conduct?
4) How will you organize your data?
5) How will you show your data? How will you analyze it - graphs?
6) What is an enzyme?
7) What is the substrate of the enzyme peroxidise? Catalyse?
8) What is the effect of adding sodium hydroxide to an anqueous solution? What is the effect of
adding hydrochloric acid?
Part 2: Conducting the Lab
Test it! Record it!
Checking the Plan:
1. What is the independent variable?
2. What is the dependent variable?
3. How will you set up a control?
4. Do you have your data collection chart/table?
* Be sure to have these answers before conducting your lab
REMINDER – You will be working with Hydrogen Peroxide, which can be a dangerous acid. Use extreme
caution and WEAR GOGGLES AT ALL TIMES!!!
Part 3: Post Lab
Analyze it! Discuss it!
1) In your groups, answer the questions that relate to your tested variable.
2) New groups will be formed with each member coming from a different experiment who tested a
different variable. Members will take turns discussing their labs and must answer all of the analysis and
discussion questions regarding all the variables.
Analysis:
Temperature
1. How does temperature affect the activity of catalase/peroxidase? Explain your observations by
discussing the effective temperature on protein structure. Discuss both high and low
temperatures. At what temperature did the enzymes work best?
pH
1. How does pH affect the activity of catalase/peroxidase? Explain your observations by discussing
the effect pH on protein structure. Discuss both high and low pH. At what pH did the enzymes
work best.
Substrate Concentration
1. How does substrate concentration affect the activity of catalase/peroxidase? How does the activity
change as the concentration change?
Enzyme Concentration
1. How does enzyme concentration affect the activity of catalase/peroxidase? How does the activity
change as the concentration change?
1.
2.
3.
4.
5.
Discussion Questions:
What did this investigation indicate about the activity of peroxidise?
What was the purpose of using control samples?
Explain why people are placed in ice baths when they have a really high fever?
If you have ever used hydrogen peroxide as an antiseptic to treat a cut or scrape, you know that it
foams as soon as it touches an open wound. Account for this observation.
Why does the stomach contain a lower pH than the rest of the body??
REMINDER – You will be working with Hydrogen Peroxide, which can be a dangerous acid. Use extreme
caution and WEAR GOGGLES AT ALL TIMES!!!