the aim of this investigation was
to observe the reaction between an enzyme and its substrate. The enzyme used
was celery juice and the substrate was hydrogen peroxide.
Over time hydrogen peroxide will
break down into water and oxygen. To speed this reaction up a catalyst can be
Enzyme molecules have active
sites that are specific to particular substrates. Meaning they accommodate
certain substrate molecules that have complimentary structures. It is known as
the lock and key model. When pairs of enzymes and substrate molecules fit
together and compliment each other they bind and are known as an enzyme
substrate complex. Reaction then takes place and the result is a spilt or
changed substrate. The basic mechanism by which
enzyme catalyze chemical reactions begins with is the binding of the substrate to the active site on the enzyme. The binding of the
substrate to the enzyme causes changes in the distribution of electrons in the
chemical bonds of the substrate and ultimately causes the reactions that lead
to the formation of products. The products are released from the enzyme surface
to regenerate the enzyme for another reaction cycle. The active site has a
unique geometric shape that is complementary to the geometric shape of a
substrate molecule, similar to the fit of puzzle pieces. This means that
enzymes specifically react with only one or a very few similar compounds.
Below is a diagram of
the lock and key model.
In the investigation the variable used was concentration. The strongest
concentration 100% hydrogen peroxide will be the most active and with the
lowest average time and highest rate of reaction. This hypothesis is based on
the collision theory. Increasing the concentration means that there will be
more molecules with the right amount of activation energy and so more successful
collision and a faster rate of reaction. There is a chance the rate of reaction
may be similar for multiple concentrations if saturation point is reached.
Below is a prediction of the graph from the experiment.
Method – see appendices
To prevent any accidents the following risk assessment was followed:
Bags and coats were safely stored away to prevent any trips or falls to
any of the scientists. This was a relatively low hazard risk.
Lab coats were worn to protect the scientist’s clothes from any
chemicals. This was a low hazard risk.
Goggles were worn to stop eyes from being touched or rubbed and to
protect the eyes from any chemicals. This was a low hazard risk.
No food or drink was present in the lab during the experiment for
personal safety risks. This was to prevent airborne materials settling or
condensing on food or food surfaces. This was a low hazard risk.
Care was taken when handling sharp items to prevent any cuts or injuries.
This was a low hazard risk.
Extra attention was made when handling chemicals to prevent any spillages
or the risk of the chemical touching the eyes or skin and therefore needing
medical attention. This was a low hazard risk as the hydrogen peroxide used was
less than 1.5M. (See the CLEAPSS sheet in the appendix)
Hands were washed with soap and water immediately after working with the
lab chemicals to prevent the chemical from touching the mouth by hand transfer
or nail biting. This was a low hazard risk.
% Concentration of hydrogen peroxide
Time taken in seconds (s)
Time taken in seconds (s)
Time taken in seconds (s)
Average time in seconds (s)
Rate of reaction 1/T (S )
Interpretation of the results
To calculate the average (mean)
the 3 recorded results are added together and divided by 3. To calculate the
rate of reaction, the average time was divided by 1.
From the results in the table
two graphs were drawn. Graph A to show the affect of substrate concentration on
the rate of reaction, and Graph B shows the affect of changes in concentration
of the substrate on the rate of reaction.
From the graphs it can be seen
that the rate of reaction increases as the concentration increases. The 100%
concentration has a rate of reaction of 0.12 seconds whereas the 20%
concentration has a rate of reaction of 0.04 seconds. These results illustrate
the collision theory as accurate. When the concentration was higher the more
successful collisions occurred. The hypothesis was proved correct. The results
table shows that the fastest rate of reaction occurred in the 100%
concentration of hydrogen peroxide. It could be said that this is the optimum
concentration for successful enzyme substrate complexes to occur. There were a
couple of anomalous results. The first recording for 100% concentration came
out at 11.93 seconds. As the other concentrations had already been recorded
this reading appeared higher than expected. The stop watch was checked and
found to be temperamental, therefore a new stop watch was used and the
recording was taken again, giving a reading of 8.69 seconds which was more
acceptable and in line with other results.
The range bars in graph A are all within an appropriate distance to each
other with one exception at 80% concentration where the difference between the
highest and lowest reading is 2.93 seconds. The first reading for 80% concentration
is quicker than the other two readings and possibly an unfair result due to
human error in reading the time on the stop clock. Our graph shows a curve and does
not plateau and therefore shows that saturation point was not met. This may be
due to the concentration of the hydrogen peroxide. Although it was 100%, the
strength was less than 1.5M. If we had used a higher strength of peroxide, the
graph line would have eventually gone into a straight line and plateaued
showing that saturation point had been met.
The method of this
investigation was simple and the instructions were followed accurately. However
human error would have taken place during the investigation that may have
altered the results. The pieces of cardboard were not precisely measured when
being cut, resulting in unequal sizes. The time the cardboard was left to soak
in the celery juice was not measured or recorded. Meaning some pieces may have
been saturated with more catalase and therefore having a higher concentration. The
exact concentration of enzyme catalase was unknown as it was obtained from
celery juice. Reading the measurements of the peroxide wasn’t 100% accurate due
to bumps in the table. Using a stopwatch raised concerns, knowing exactly when
to press stop and start was not always easy to determine.
investigation was to be repeated some factors could be improved to give more
accurate results. The pieces of cardboard could be measured and cut so that
every piece is exactly the same size, alternatively commercially bought pre-cut
filter paper could be used. Using a different catalase would improve the accuracy
of the results such as a pure catalase. The use of a water bath to control the
temperature of the catalase would have been an improvement on the accuracy of
the results. Using a gas syringe or measuring cylinder to measure the exact
amount of oxygen would be a superior way to accurately read the results. The volume of gas is
determined by reading the scale on the side of the gas syringe.
Below is an image of a gas syringe.