The Effects of Temperature On the Digestion of Starch
For my experiment, I will be looking at enzymes; more specifically,
the enzyme amylase. Amylase breaks down starch into glucose. I will be
looking at how temperature affects this conversion.
Enzymes exist in all living things. They are composed of polypeptide
chains of amino acids
and are produced in living cells. Each cell
contains several hundred enzymes, which catalyse a vast number of
Enzymes are known as 'Biological Catalysts' as they dramatically
affect the rate at which reactions occur within living organisms,
without being 'used up' or effecting the reaction in any other way.
Enzyme catalysis saves the need for an increase in temperature in
order to speed up reactions within living things. Such an increase in
temperature would be lethal to the organism. Enzymes only control the
rate of one specific reaction inside the body, as only one specific
substrate can fit into its active site; therefore we say the enzyme is
There are two main types of enzyme:
* Intracellular enzymes, which control reactions that occur inside
* Extracellular enzymes, which control reactions that occur outside
All enzymes are affected by temperature and pH. They have an optimum
range of the two, and anything outside this range will denature the
enzymes "active site." The enzymes that are used in reactions inside
our bodies have an optimum temperature of 37oC. The enzyme can
withstand a few degrees either side of this temperature; but any
higher will cause the protein structure to break apart and stop
working, because the bonds that hold the amino acids together are
relatively weak; therefore, a high temperature would cause the atoms
to excite and the bonds to break.
The enzyme will become denatured permanently and no longer functional.
The optimum pH for an enzyme depends upon where about in the body it
is working. Generally, most enzymes have an optimum neutral pH of
around 7, but enzymes that work in the stomach, for instance, have a
much lower optimum pH of 2 due to the acidic environment.
I predict that as the temperature increases, so will the rate of the
reaction. I think this because when heat is applied, it excites the
particles more and as a result, they collide faster and so the
reaction rate increases. When a particular temperature is reached, I
think the rate of reaction will dramatically decrease because the
amylase is working outside its optimum temperature range. Usually a
rise of about 10oC will double the rate of reaction. After the enzyme
reaches its limit, which I predict to be 40oC, I think the reaction
rate will decrease rapidly and then stop. I think this because the
enzyme has become denatured and the bonds holding the enzyme together
have started to break; therefore denaturing the active site.
* 20ml Starch
* 20ml Amylase Solution
* Water Bath
* Ice Bath
* Boiling Tubes
* Test Tubes
* Bunsen Burner
* Spotting Tile
* Measuring Cylinder
* Test tube rack
To keep my experiment as fair as possible and to achieve the best
possible results, I will keep the following aspects of my test
Amount and concentration of starch solution, Amount and concentration
of amylase solution, amount of iodine solution, amount of benedict's
solution added and pH.
The only variable in my experiment will be the temperature change, as
this is the objective of my test.
· Safety Precautions:
Throughout my experiment I will be handling chemicals; some of which
are dangerous. I will also be using a Bunsen burner throughout the
experiment so I will be taking certain precautions. First of all I
will wear goggles from the start of my test to the very end. I will
use tongs to handle the boiling/test tubes when they are taken out of
the hot water bath. If any other safety precautions arise during the
experiment, I will take certain measures to make them as safe as
I will set up my experiment as instructed below:
20ml Starch &
(All boiling tubes above have the same amount of starch and amylase
* Using a 100ml measuring cylinder, I will measure out 20ml of both
Starch and Amylase solution.
* Put the 20ml of amylase and starch solutions in separate test
* Next, I will cool/heat an ice/water bath to 5oC (or the chosen
temperature) and add a thermometer.
* Wait for the temperature to reach a constant.
* Add both test tubes of amylase and starch into the ice/water bath.
* Wait until both solutions reach the temperature of the ice/water
* When both test tubes are at the correct temperature, add them
together into a boiling tube.
* Place the boiling tube into the ice/water bath to keep the
* Once the amylase and starch solutions have been added together
start the stopwatch.
* Every 30 seconds, using a pipette, take a sample from the boiling
tube and add it into a spotting tile.
* Add 2 drops of iodine solution to test for the presence of starch
and wait for the solution to change to a black/purple colour.
* Repeat this every 30 seconds until the solution no longer changes
colour; therefore indicating all the starch being converted into
* Once the iodine stops indicating a black colour, stop the
* Record the indicated time on the stopwatch into the results table
* Then, add a few drops of Benedict's to the solution and put the
boiling tube into a hot water bath.
* Wait until the solution has turned a brick red colour; thus
indicating all the starch being turned into glucose.
The same process as above should be carried out for every experiment.
(A, B, C, D, E, F and G.) When using a water bath instead of an ice
bath, set this up by adding water into the bath. Light the
Bunsen-burner and keep it on a safety flame until the Bunsen is being
used to heat up the water. When the water reaches the correct
temperature, pull the Bunsen away to keep the water from overheating.
After completing my experiment, my results are given below in a table.
I have also plotted my results onto scatter graph to show the variance
in time against temperature.
Time taken for starch to be digested (min)
[IMAGE] A 5 14
B 15 11
C 25 8
D 35 3
E 45 9
F 50 13
G 65 No Reaction
In conclusion, from the results of my experiment, I can see that the
basic theory behind my prediction was proved correct. From my graph
above, I can see that as the temperature increased towards the
temperature of the human body (37oC); the reaction time taken for the
amylase to digest the starch fully decreased. This is because the
amylase was working at its optimum temperature of around 40oC.
At the start of the experiment, the amylase took quite a long time to
digest all of the starch present. This is because the enzyme was not
working in its ideal range, and so the reaction time was high. As the
temperature slowly increased, the reaction time generally got less,
which is shown in this part of the graph as a negative correlation. At
15oC, the amylase was still working outside its optimum range, and so
as a result, the time taken to digest was still relatively high. As
the temperature was still rising, the reaction time was continually
falling. At 25oC the enzyme was nearing its optimum range. This is
shown in the graph and the results table by the time it took to
digest, 8 minutes. Still at this point, the graph shows negative
When the starch and amylase where tested at 35oC, the reaction time
was pretty fast. All the starch was digested within 3 minutes of the
start time, as indicated by the graph. This small reaction time shows
that 35oC is the optimum temperature for the amylase to work within.
In my hypothesis I predicted that around 40oC would be the best
temperature, because this is the closest to the normal temperature of
The next temperature tested was 45oC. At this time, the amylase had
started to go outside its optimum temperature range once again,
therefore the enzymes' active site becoming damaged by the heat. The
heat of the substances would cause the protein structure to break
because of the weak bonds holding it together. This damaging of the
active site is irreversible, and so slowly the amylase solution would
get less and less effective. This is shown by the graph as an increase
in the reaction time (positive correlation.)
The next temperature tested was 50oC. At this stage, the amylase took
13 minutes to digest all of the starch, which is a poor time compared
to the time it would normally take at its optimum temperature. By now,
most of the enzymes' active site would have been partially denatured,
if not fully. The graph continues to rise to show a longer reaction
The final temperature tested for the digestion
of starch, was 60oC. At
sixty degrees centigrade, the amylase had become fully denatured. An
irreversible affect. All the starch present in the solution would
never be converted into glucose because of the damaged amylase enzyme.
The basic findings from my experiment have been successfully
scientifically proven. I have carried out the experiment to the best I
possibly could, but given a number of other situations, I feel that I
could have made the experiment fairer and more accurate.
The main aspects I feel I could improve my experiment on are:
Temperature control and accuracy of results.
To control the temperature of the water baths, for the digestion to
take place at the chosen temperature, I could have got better, fairer
results by the use of an electric water bath. If I had the use of an
electric water bath, I could have kept the accuracy of the test
better, resulting in more accurate results.
Another main aspect I could improve on for my experiment is to make
the results I received from my test fairer. I could achieve this by
repeating each test three times and then taking the average time from
the three. This would have given me a more likely result time for the
I could also increase the time from which I took a sample from each
boiling tube. Instead of taking a sample every 30 seconds, I could
take a sample every 10 or 15 seconds. This would result in a truer
reaction time. I could also take a wider range of temperatures to
pinpoint the specific optimum temperature, and the specific
temperature that the enzyme denatures. I could do the same experiment
changing the pH of the solution, to see how that affects the enzyme
and which pH is the best for the conversion of starch into glucose
One other aspect to take into account on improving my experiment is my
own personal practical skills. I feel that I carried out the
experiment to the best of my ability. During the experiment I could
have kept a little more level headed and patient, so that I could pay
more attention to the task and receive better results. If I had a
little more time to complete the experiment, and things where not as
rushed, then I feel I could have improved on the accuracy of my