1. Preston Fernandez Optimal pH of Liver and Potato Catalase Reactivity HL BIO P.8
Introduction
Enzymes are globular proteins that catalyze chemical reactions in all living organism.
Enzymes catalyze these reactions by breaking apart the bonds of a substrate on the active site
(as shown on the diagram below).
There four variables that influence the rate at which enzymes catalyze substrate, these being:
temperature, substrate concentration, enzyme concentration and pH. pH is a measurement
between 1 and 14 which indicates how acidic or basic a substance is, where a pH of 7 is
neutral and neither basic or acidic. Catalase is an enzyme found in chicken liver and potatoes
which catalyzes the decomposition of hydrogen peroxide (H2O2) into oxygen (O2) and water
(H2O). The catalyzation of hydrogen peroxide is represented in the formula below.
H2O2--------------- Catalase------------ 2 H2O + O2
As mentioned earlier both potatoes and chicken liver have catalase, however the environment
of a potato is much different than chicken liver. Chicken liver has an alkaline environment
due to the daily production of digestive bile which is basic. Potatoes have a more stable and
neutral environment within them. Despite these two starkly different environments, the
catalase enzyme proves to be present and working in both.
Although most enzymes work at an optimal pH level of 7, some enzymes work at an optimal
level that fits the environment that surrounds them.
Research Question: How will pH effect enzyme activity in catalase extracted from potatoes
in contrast to catalase extracted from chicken liver?
The independent variable in this experiment is the pH of the environment that the catalase
will be catalyzing in (pH 5, pH 7, pH 9) and the dependent variable is the rate at which the
catalase breaks down the hydrogen peroxide into water and oxygen.
Numerous variables can affect enzyme activity and thus will be controlled. The
concentration of the enzyme will be kept constant for all trials, as alterations of enzyme
concentration can affect enzyme activity. The concentration of the substrates will be kept
constant for all trials, as this is another variable that can affect enzyme activity. Temperature
of enzyme, pH and substrate solutions will be kept constant at room temperature, to minimize
discrepancy as temperature of either substrate or enzyme can affect enzyme activity.
Materials
45 ml 20% Chicken Liver 2 Hole Rubber Stopper Computer
45 ml 10% Potato Solution Syringe LabPro
3ml each pH (5,7,9) 3 x 10ml beakers LoggerPro
1% Hydrogen Peroxide 10ml Test Tube Gas Pressure Sensor

2. Preston Fernandez Optimal pH of Liver and Potato Catalase Reactivity HL BIO P.8
Method
1. Two enzyme solutions were made. The potato solution was made up of 10grams of
potato blended with 100ml of water. The chicken liver solutions were made up of 20
ml of chicken liver blended with 200ml of water. Although percent concentration
differs between the two solutions, this is not a variable, as the data of reaction rate
would then be manipulated into percents, where this would be insignificant.
2. For every trial, 3ml of hydrogen peroxide solution was placed in a test tube with 3ml
of a pH buffer. The test tube would be shut with the 2 hole gas stopper, one hole was
for the injection of the enzyme solution as the other hole was connected to the gas
pressure sensor, which would record the pressure of the test tube, allowing for the
determining of the enzyme reaction rate. (The diagram below represents the setup of
this lab)
3. Collection of data began prior to the injection of the enzyme into the hydrogen
peroxide/pH solution. Data collection was graphed through the LoggerPro software
which was connected to the LabPro hardware, further connected to the gas pressure
sensor probe.
4. Once the enzyme reactivity diminished, data collection was stopped, and the gradient
of the graph was recorded using a LoggerPro, prior to the graph’s plateau. This
gradient is the reaction rate.
5. 5 trials were collected for each pH (5,7,9) under both catalase solutions.
Syringe
Gas Pressure Sensor
Test Tube Stopper
Test Tube
LabPro Hardware
Computer/LoggerPro

3. Preston Fernandez Optimal pH of Liver and Potato Catalase Reactivity HL BIO P.8
Results
Liver and Potato Catalase Reactivity Rate at Varying pH
Liver Catalase Reactivity Rate at Varying pH Potato Reactivity Rate at Varying pH
kPa/s ± 0.01 kPa/s ± 0.01
pH T1 T2 T3 T4 T5 Avg. T1 T2 T3 T4 T5 Avg.
5 1.365 1.299 1.942 - - 1.536 .03431 .03647 .03471 .03560 .03629 .03548 ±
± .00108
.322
7 6.629 6.740 6.241 - - 6.540 .03764 .03949 .04022 .03927 .04212 .03957 ±
± .00180
.250
9 5.000 6.756 6.106 - - 5.954 .03217 .03514 .03349 .03632 .03541 .03451 ±
± .00208
.878
The table above is the raw data table collected during the experiment.
Additional Observations
- Liver catalase solution had “chunks” of liver floating in it
-Potato catalase solution had potato chunks floating in it
-When enzymes were injected into hydrogen peroxide/pH solution bubbles began forming on
the surface and in the solution
-Syringe may have absorbed some of the gas, the possible cause of depression on the some of
the graphs
-The rubber stopper popped off when the pressure in the test tube reached a certain point
-Potato was used on different days, freshness changed
Sample Graph
Graph above is trial 5 of pH 7 for potato catalase. As seen in graph the gradient is recorded
as it represents rate of reaction. The spike at the beginning of the graph is the insertion of
enzyme, pressure decreases as some filled the syringe used to inject enzymes.

4. Preston Fernandez Optimal pH of Liver and Potato Catalase Reactivity HL BIO P.8
Sample Calculations
Calculating Average Uncertainty
Manipulating Averages into Percentages (The concentration of enzyme is different for potato
and chicken liver, by converting the averages into percentages it will be easier and more
realistic to compare and contrast the catalase in potatoes to the catalase in enzymes)
Above are the formulas used to calculate the averages into percentages.
The Calculations Shown below is the manipulation of averages to percentages for chicken
liver.
Processed Data Table
Optimal pH of Liver Catalase and Potato Catalase Enzyme Reactivity
% Optimal pH of Liver Catalase % Optimal pH of Potato Catalase
Enzyme Reactivity Enzyme Reactivity
pH Avg. kPa/s % Optimal Avg. kPa/s % Optimal
5 1.536 23 .03548 86
7 6.540 100 .04123 100
9 5.954 91 .03451 84
The table above is processed data that shows the % optimal the catalases are at different pHs

5. Preston Fernandez Optimal pH of Liver and Potato Catalase Reactivity HL BIO P.8
Processed Graphs
Note* The graphs share the same X-axis and Y-axis units, so they can be compared directly.
Liver Catalase Optimum Vs. pH
120
% of Optimal Reactivity
100
80
60
40 Series1
20
0
5 6 7 8 9
pH
The graph above shows the correlation between percent Optimal of liver catalase against pH
Potato Catalase Optimum Vs. pH
120
100
80
% Optimal
60
40 Series1
20
0
5 6 7 8 9
pH
The graph above shows the correlation between percent Optimal of potato catalase against
pH.

6. Preston Fernandez Optimal pH of Liver and Potato Catalase Reactivity HL BIO P.8
Conclusion
Results show differing affects of pH on the catalase of potatoes compared to catalase of liver.
Potato catalase was at 100% optimal level at pH 7, and as the pH became more acidic or
basic, the efficiency of the enzyme decreases, almost equally, thus graphing a parabola shape.
Potato catalase had an 84 % optimal level at pH 9 whereas, pH 5 was 86%, which suggests
that the further away the environment is from pH7 the less reactivity levels the potato
catalase, performs at. The liver catalase however, did not decrease equally as 2 pH levels
were increased or decreased. Rather as the pH increased, the optimal level remained steady,
over 90% but as the pH decreased into an acidic solution, the enzyme reactivity drastically
dropped from 100% optimal level performance at pH 7 to 21% optimal level performance at
pH 5. The results suggest that enzymes are fit for their environment, and work at optimal
levels when their surroundings are identical to that of where they catalyze reactions. As
mentioned in the introduction, the liver catalase would most likely have higher reactivity in a
environment of alkaline, as liver produces alkaline bile for digestion, and have less reactivity
in an environment that is acidic because it would be useless in a basic environment. The
result show that in between ph 7 and ph 9, reactivity is near or at its highest, and the
theoretical pH level of the liver is about 8. The congruence with the theoretical data and the
data collected show an even greater correlation between optimal performance of liver catalase
and pH. And finally potato catalase would seem optimal at pH 7, since the potato is an
environment of neutral conditions.
The results that were collected from the optimal % levels and pH of potato catalase is
identical to the general trend of most other enzymes. This trend is that pH 7 is the pH of
optimal enzyme reactivity. As well as pH increases or decreases, the enzyme reactivity
decreases.
Unlike the trend of most enzymes, liver catalase does not decrease as pH increases past pH 7,
rather it maintains a steady reactivity rate and does not drop. Liver catalase has a wider range
at which it can perform at optimal levels, between pH 7 and pH 9, however the performance
of the enzyme severely diminishes once it is in an acidic atmosphere where it is denatured
and less likely to catalyze hydrogen peroxide.
Limitations
There are several limitations of this lab. Procedural limitations firstly consist of the small
number of trials done on liver and pH. Maximizing the trials on each pH from 3 to 5 would
have been beneficial to data collection and manipulation as it increases the confidence of
what the data has to express. Another procedural limitation, is that the data is only limited to
3 pH’s. The data could have benefitted more if there was a larger range and/or smaller
increment between pH. This would have been beneficial, as it would allow the identification
of smaller details and how the enzymes worked under more various conditions.

7. Preston Fernandez Optimal pH of Liver and Potato Catalase Reactivity HL BIO P.8
Limitations in the experiment itself, was the possible pollution of test tubes. If all lab ware
had not been perfectly clean, chemical remnants of past experimentation could have thrown
data. Because the experimentation was over a period of time, the room temperature could
have differed one day to the next which could have altered data, as temperature is a factor
that influences enzyme reactivity. As well, the use of old potato could have been a
discrepancy as the dried out and old potato probably had a larger concentration of already
denatured enzymes; this could have been an anomaly in the data as well.
Modifications
This lab would have been more successful if there had been more trials. More trials suggest
less error and higher confidence in data. Secondly a wider range of pH and smaller
increments from on pH to another would be added. This would be to increase significance as
well as find minute and more intricate details in the data because of the larger range.
Reassurance of washed and dried Labware should be made aware of in the lab, to prevent
experimenters from polluting their own data or other’s data. If experimentation takes place
during multiple sessions, temperature should be recorded for reference, just in case it does
cause a discrepancy in the data. And finally, fresh potatoes should be used after each and
every session, and if possible use the same potato and obtain all trials needed from that potato
in that one session. This decreases the amount of discrepancy from changing the potato, and
allowing the enzymes in the potato to denature.