The Effect of Substrate Concentration on the Rate of Reaction Between Yeast Catalase and Hydrogen Peroxide

The Effect of Substrate Concentration on the Rate of Reaction Between Yeast Catalase and Hydrogen Peroxide

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The Effect of Substrate Concentration on the Rate of Reaction Between Yeast Catalase and Hydrogen Peroxide

Useful info

The Enzyme Catalase is a protein molecule which is found in living
cells. It is used to speed up reactions in the cells. It is a very
specific enzyme and just performs one particular reaction.

Catalase is an enzyme found in cells in potatoes and liver and is used
for removing Hydrogen Peroxide from the cells. Hydrogen Peroxide is
the poison produced during metabolism. Catalase aids the decomposition
of Hydrogen Peroxide the by products of which are water and oxygen as
shown in the equations below.



Hydrogen Peroxide-------------->Water + Oxygen



It is able to speed up the decomposition of Hydrogen Peroxide because
the shape of it's active site is the same as that of the Hydrogen
Peroxide molecule. This is the type of reaction where a molecule is
broken down into smaller pieces and is called an anabolic reaction.


Enzymes are catalysts which means they speed up reactions and allow
them to take place more easily using less energy. They do this because
they each have a specialized active site which is designed to fit a
specific molecule. (Pepsin= Protease which catalyses reactions
involving proteins) etc Every type of enzyme has a different shaped
active site and likes to work in different conditions some like more
neutral conditions others like acidic conditions the conditions vary
from enzyme to enzyme.

Active site shape Diagram

When an enzyme works there are different conditions which inhibit
enzyme activity:

Ÿ PH level

Rate of reaction


Ph level

Enzymes work best at certain Ph levels , the optimum rate of reaction
for the enzyme is obtained between these PH levels if they stray to
far from these ph levels the cease to work a efficiently

Ÿ Heat

Rate of reaction



Enzymes work best at certain temperatures around these temperatures

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the rate of reaction will be at its peak if they stray to far from
these temperatures the cease to work a efficiently and can become

Ÿ Substrate concentration

Rate of reaction


Substrate conc

Substrate concentration directly raises the rate of reaction up to the
point where there is to much substrate and not enough active sites to
catalyse it , the rate of reaction the levels off.

Ÿ Enzyme concentration

Rate of reaction


Enzyme conc

Enzyme concentration is directly proportional to the rate of reaction

The Apparatus I will Need For the tests.

Gas Syringe

Metal Stand

Yeast Catalase

Hydrogen Peroxide

Test Tubes


Test Tube Rack

Stop Watch


Pipette Filler

Tap Water


1. Put 2cm3 of yeast into one test tube. And 4cm3 of hydrogen peroxide
solution at a concentration of 20% to the other test tube. Use a
pipette to measure the volumes. It is very important to measure the
amounts of Hydrogen Peroxide , Yeast and water accurately , to ensure
it is a fair test.

2. Pour the hydrogen peroxide into the test tube that contains the
yeast and immediately put the gas syringe bung on the end of the test
tube immediately , at the same time start the stopwatch.

3. Bubbles should start to rise up the tube and the gas syringe will
move outwards, when the volume of gas inside the gas syringe reaches
the 30cm3 mark stop the clock and note the time to the nearest 1/10th
of a second.

4. Repeat the experiment with hydrogen peroxide concentrations of 16%,
12%, 10%, 8% and 4%. The table below shows what amounts of Hydrogen
Peroxide and water are needed to make the solutions.

Concentration Of Hydrogen Peroxide

Volume Of Hydrogen Peroxide (cm3)

Volume Of Water (cm3)
















5. Repeat the tests at least three times so that you can work out an
average. Repeating the experiments several times will produce better ,
more accurate results as inaccuracies in one experiment should be made
up for by the other experiments.

I am going to use yeast catalase as opposed to catalase from apples,
potatoes or liver .

To ensure this is a fair test all the variables except for the
concentration of the Hydrogen Peroxide must be kept the same for all
of the experiments. Variables that must not be altered include:-

The temperature of yeast, the temperature of Hydrogen peroxide, the
yeast concentration, the batch of yeast, the volume of yeast and the
volume of hydrogen peroxide.

When measuring out the volumes of Hydrogen Peroxide, Yeast and Water
the measurement should be taken by looking at the scale at an angle of
90 degrees to it to avoid any errors while measuring .

My Prediction

I predict that as the substrate concentration increases, the rate of
reaction will increase at a rate that is directly proportional to the
rate to the increase in the substrate concentration until the solution
is saturated with hydrogen peroxide. When this point is reached,
adding extra substrate will make no difference to the rate of the

Once the number of substrate molecules added is more than the number
of active sites which are unfilled then the rate of reaction will no
longer go up. This is because the maximum number of reactions are
taking place at once so any more substrate molecules have to wait
until some active sites are no longer in use.


When I carried out the experiment I got these results.

Hydrogen Peroxide Concentration








Time Taken (Test 1) (secs)







Time Taken (Test 2) (secs)







Time Taken (Test 3) (secs)







Average of the Tests (secs)







Rate=30/Average (Cm3/second)








The average results are written down to one decimal place because it
is impossible to get accurate times to two decimal places , because
our reaction times are not fast enough to stop the clock that
accurately .

From these results I was able to plot a graph of the rate of reaction
against concentration of Hydrogen Peroxide.

Graph To show the volume of oxygen produced per second.


Of Oxygen Produced per second



Substrate concentration

Analysis of results

When the Hydrogen Peroxide concentration is increased, the rate of
reaction increases at a directly proportional rate until the
concentration of Hydrogen Peroxide reaches about 16%. When the
concentration doubled from 8-16% the rate of reaction went up from
1.65-2.97 Cm3 Oxygen produced per second, which is an increase of 1.8
. I expected the rate of reaction to increase twice when the Hydrogen
Peroxide concentration was increased twice because there were twice as
many substrate molecules which could join onto the active sites of the
enzymes . The reason that the number is less than double could be
because at 16% the Enzyme's active sites may already have been close
to being saturated with Hydrogen Peroxide. There may also have been an
experimental error which caused inaccuracies.

After 16% the increase in the rate of reaction slowed down. This is
shown by the curve of the graph starting to level out . At this point
almost all the active sites were being used so the active sites were
said to be saturated with Hydrogen Peroxide. Increasing the Hydrogen
Peroxide Concentration after the point of saturation had been reached
would not have caused the rate of reaction to go any faster . All the
active sites were being used so any more Hydrogen Peroxide molecules
would have had to wait until an active site became vacant.

The optimum rate of reaction ,theoretically, is when all the active
sites are being used but in reality this is never reached because not
all the active sites are being used at the time.

Factors that Limited the experiments accuracy

To help make my experiment more accurate, I repeated each test three
times and then averaged all the results to plot the graph. I tried to
keep the variables except the concentration of Hydrogen Peroxide the
same for all of the experiments.

There are a few factors which may have made the experiment less than
perfectly accurate such as :

The miniscule delay between mixing the Hydrogen Peroxide and the yeast
, putting the bung on top of the beaker and starting the stopwatch.
This will effect all the results but I carried out all the three steps
in the same way every time so it should not make a noticeable
difference to my results.

Anomalous results

The plotted points on the graph give a straight line of best fit at
beginning which then curves off steadily as the reaction slows . The o
anomalous results are the ones at 8% and 10%. The one at 8% is
slightly above the line of best fit and the 10% result is slightly
below it. This is probably due to an error involving the factor I
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