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IB Biology - Internal Assesment
What is the effect of different temperatures on the rate of reaction of catechol oxidase during the
oxidation of potato flesh?
May 24, 2017

Research Question:
What is the effect of different temperatures (7, 25, 30, 40, and 55 ​℃​ ) on the rate of reaction of the
enzyme catecholase (catechol oxidase) during oxidation (browning) of potato flesh?

Hypothesis:
If I am able to achieve and utilize temperatures varying from 22 to 45 ​°C then the enzyme ( catechol
oxidase) will work at its optimum temperature and at its highest rate when catalyzing the browning
and oxidation of the potato because this is the range of optimum temperature for this specific enzyme
and if a lower or higher temperature then the enzyme will lose its shape and denature so the reaction
will not work
...


Background Information:
Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy,
they are proteins of a specific shape which need a specific substrate to fit into their active site, they
have an optimum pH varying between neutal and weakly basic as well as temperature and substrate
concentration at which they work best
...
Usually enzymes denature and lose their shape at about 45 degrees celsius
...
I will also
be using 0
...
We will be using catecholase from
potatoes but it can be found in many different fruits and vegetables such as apples, bananas etc
...


1

Spectrophotometre Light absorbance:

Spectrophotometry is a meausre used to indicate how much light can a substance absorb, it is obtained
by measuring the intensity of light when passing through certain substances
...


2

Table 2) Controlled variables
Control Variables

Units

Possible effect on results

Catechol concentration (0
...
1%

A different concentration
would be too strong and it
could cause the reaction to not
work or work too fast
...


Catechol Storing Temperature

Room temperature measured at
the time 18​°C

Because this is the ideal storing
temperature, if it is changed
this could affect the results of
the reaction
...


Amount of catechol for each
temperature and each trial (3
ml)

3 ml

If there is more catechol then
this substrate could accelerate
the reaction or saturate it so it
could not work
...
Peel 1 potato and using a cutting board cut both of them in small cubes or strips, then using a
top pan balance measure 80g of the cut up potato (no skin)
...
Using a 200 ml measuring cylinder, measure 200 ml of distilled water, add them to the
blender with the 80g of cut up potato, plug the blender, put the lid on the blender and blend
until a soft paste is formed
...
Add the potato extract to the 500 ml beaker
...
Set the wavelength of the spectrophotometer to 200 to 1000nm
5
...

3

6
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In tube 1, 3 ml of potato extract were measured using a measuring cylinder
...
(water was cooled by being cooled in a freezer until the thermometer measured 7
degrees celsius)
...
In tube 2, 3 ml of Catechol substrate (to speed up the production of benzoquinone) were
measured using a measuring cylinder and a pipette
...
The contents of tube 1 and tube 2 were mixed, and 3 ml of the mixture were placed into the
cuvette and then placed into the spectrophotometer
...

10
...
And the placing of
the wavelength
...

Cutting of the potato must be done carefully because sharp tools are being used
...
05 ​℃​)
- 1 stopwatch (± -0
...
1% catechol
- Hot bath
- 110 ml of potato extract
- Tape and pen
- Blender
- Top pan balance (± -0
...

- 200 ml of distilled water (for potato extract)
- 500 ml beaker

4

Raw and Processed Data:
Tables:
Table of data #1)
Absorbance of benzoquinone for each trial (10) and temperature (​7, 25, 30, 40, and 55 ​°C)

Table of data #2)
Mean absorbance for each temperature (7, 25, 30, 40, and 55 ​°C) and standard deviation
...
376

0
...
408

0
...
412

0
...
438

0
...
399

0
...
If a lower or higher temperature was used then the enzyme would
denature and the reaction wouldn't be as efficient
...
1% catechol substrate was used also to speed up the reaction, according to my investigation, the
higher the absorbance the more benzoquinone is produced therefore the reaction occurred at its
optimum rate
...
The mean absorbance for these temperatures were 0
...
412 nm for 30 °C, and 0
...
At the lowest and highest temperatures (7, and 55°C)
the absorbance was low at 7 degrees and then at 55 it decreased because the enzyme denatured and the
rate of reaction decreased
...

According to my results I can say that the optimum temperature for the enzyme to work is 40 because
this temperature produced the highest absorbance, this is because the catechol oxidase catalyzed the
reaction and the potato oxidised at a faster rate, this can be measured with absorbance because when
the potato oxidises and (rusts), catechol is the pigment which changes the colour of the potato and so
it absorbs light, so the more catechol, the higher the absorbance
...

Strengths and weaknesses:
My overall method was very accurate, I took my time and I was able to measure the results within a
good time period, each result was measured after exactly one minute and I was sure to follow my
controlled variables to achieve precise results
...

There was a random
uncertainty because the
environment was lowering the
temperature of the distilled
water quickly

Next time I could use a bunsen
burner to heat the distilled
water instead because like this
I could control the temperature
more
...


This affects the results because
if they arent mixed fast
enough, the absorbance will
not be accurate
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Bibliography:
Jensen, H
...
Catecholase reversible inactivation and reactivation
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jbc
...
full
...
(1999)
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Retrieved from
http://faculty
...
cuny
...
html
Thorpe, P
...
Enzyme exercise catechol oxidase
...
baruch
...
edu/jwahlert/bio1003/enzymes
...
(2015)
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Retrieved from
https://chem
...
org/Core/Physical_and_Theoretical_Chemistry/Kinetics/Reaction_Rates/Exper
imental_Determination_of_Kinetcs/Spectrophotometry

oes hh

8



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