Sample Lab Report
Title: The Effects of Temperature and pH on the Activity of the Enzyme Catalase
William Capitano M.S.
Abstract
Enzymes are protein catalysts that speed up chemical reaction in living organisms. This
investigation tested the effects of temperature and pH has on enzyme activity. Catalase found in
potatoes was treated with different temperature (0o, 23o, 37o and 100oC) and pH (2, 7, and 12).
Data was collected by measuring the amount of oxygen produced. The results show that catalase
does not work at extreme temperatures and pH levels. Results also suggest that high
temperatures and low pH denature proteins.
Introduction
Cells require the use of enzymes to carry on life functions. These functions include breaking
down molecules for energy, building structural molecules such proteins and producing various
chemical messengers. Because most reactions require high amounts of energy, they could not
occur in a cell without the aid of a catalyst. Enzymes are protein catalysts that bind to molecules
allowing them to react faster. This can occur without the high amount of energy the molecules
would normally need.
Enzymes work by the lock and key theory (Audesirk et al, 2008, page 50) which states that
enzymes have a particular location, called an active site, where molecules (called substrate) bind.
Because of the shape of the active site only specific molecules can enter. Any change to the
shape of the enzyme can affect its ability to bind to the substrate.
The purpose of this experiment is to measure the effects of temperature and pH on enzyme
function. The enzyme we used is catalase which is a common enzyme found in many organisms.
Catalase breaks down hydrogen peroxide producing oxygen and water.
Materials and Methods
For this experiment we followed the protocols set out in Principles of Biology Laboratory
Manual (SCCC, 2005. page 66-70)
Effects of temperature on enzyme activity
Four 10 mL test tubes containing hydrogen peroxide were incubated at different temperatures:
0oC, 23oC (two test tubes), 37oC for five minutes. A small piece of potato was added to the four
test tubes. The test tubes were corked with a #2 one-hole rubber stopper then inverted in their
water baths for 10 minutes. Gas collected at the top (bottom) of the test tubes forcing peroxide
out of the hole. The length of gas produced by the reaction was measure in millimeters using a
metric ruler.
Effects of pH on enzyme activity
Pieces of potato were added to three test tubes. The potato was treated to different pH levels:
NaOH (pH =12), dH2O (pH =7) and HCl (pH=2) for five minutes. The pH of each solution was
determined with litmus paper. The test tubes were then filled with hydrogen peroxide, stoppered
and inverted for 10 minutes at 23oC. The gas collected was measured in millimeters using a
metric ruler.
Data from other groups in Bio 101 lab was collected and averaged.
Results
The potato in the 0o, 23o, 37o all produced oxygen 37o producing the most (Table 1). Boiled
potato produced no gas. Our data was close to the class averages (Table 2) with the exception of
37oC. The groups with the different pH treatments (Table 3) were very similar to the class
averages (Table 4). HCl had the least amount of O2 produced.
Table 1 Measurements of O2 produced at different temperatures
Temperature (oC)
0
23
37
100
Length of Gas Collected (mm)
3
9
15
0
Table 2 Class data set for temperature treatments
Group 1 (ours)
Group 2
Group 3
Group 4
Average
0o (mm)
3
3
4
2
3
23o (mm)
10
9
11
10
10
37o (mm)
15
20
21
20
19
100o (mm)
0
0
0
0
0
Table 3 Measurements of O2 produced by potato treated with different pH solutions.
pH
2
7
12
Length of gas collected (mm)
1
12
6
Table 4 Class data set for pH
Group 1 (ours)
Group 2
Group 3
Group 4
Average
pH = 2
1
0
0
2
0.75
pH = 7
12
10
12
11
11
pH = 12
6
5
5
6
5.5
Discussion
The results of the temperature and pH treatments show a similar pattern. At extreme
temperatures (0oC and 100oC) there was very little activity where the most activity was at 37oC.
This indicates that catalase works best at or near mean human body temperature. This was
expected because catalase is also found in humans. Because the 0o catalase produced some
Oxygen suggests that catalase slows down at low temperatures but can still function. Boiled
potato shows no oxygen suggesting that at high temperatures permanently destroy or denature
the enzyme. Changing the shape or denaturing enzyme prevents it from acting on its substrate.
The pH extremes (pH =2 and 12) also showed little activity. Catalase treated at a pH of 7
produced the most O2. This is very close to physiological pH (7.4) (Audesirk et al, 2008, page
100). Catalase showed most sensitivity to lower pH.
Further research should include more temperatures and pH to see if there are fluctuations in
catalase activity and confirm that 37o and pH of 7 is the optimum temperature and pH for
catalase. Other sources of catalase (plant, animal, fungal) should also be investigated.
Conclusion
Treating catalase with different temperatures and pH’s for ten minutes shows that catalase found
in potatoes is sensitive to extremes but appears to work best at human body temperature and pH.
Acknowledgements
This project would not be possible without the support of Suffolk Community College,
Professional Assistant Barbara Young, and the students of Bio 101.
References
Audesirk, T., Audesirk, G., Byers, B.E., 2008. Life on Earth 5th Edition. Pearson Benjamin
Cummings. San Francisco, CA.
Suffolk County Community College. 2005. Principles of Biology Laboratory Manual. MacGraw
Hill Publishing Boston, MA