Enzymes are biological catalysts. They are made of protein. They speed up the rate of reaction in the body and without taking part in the reaction. The surface of the enzyme where the substrate binds to is called the active site, which has a specific conformation. Normally the active site is enzyme-substrate specific. This is explained by the lock and key theory, where the enzyme is the lock and the substrate is the key.
Enzyme activity, specifically is the rate at which the enzyme catalyses the chemical reaction. This is affected by three main factors: 1) temperature, 2) pH and 3) substrate concentration. Another factor is the enzyme concentration but it is not included in the syllabus.
Hydrogen peroxide is a weak acidic but has very strong oxidizing properties. It is a by-product of respiration thus very harmful to cells. Hydrogen peroxide is catalysed by the enzyme catalase to form water and oxygen in the body as soon as possible:
2H2O2 (l) catalase 2H2O (l) + O2 (g)
The enzyme catalase can be found mostly in liver cells and in potato and many other plant foods.
To investigate the oxygen collected in hydrogen peroxide using different sources of plant food samples.
Investigating how will the height of foam (showing oxygen collected) differentiate the activity of the enzyme catalase using different plant sources (potato, apple, onion, beetroot, carrot) at optimum temperature (37oC) in a period of 20 minutes?
How will it be control
(type: controlled variable)
Boil water in a kettle, and then pour in a beaker to create a water bath. Mix the food samples with the hydrogen peroxide in test tubes and place them in the water bath
Oxygen collected from the decomposition of hydrogen peroxide
(type: dependent variable)
The height of the foam found on the side of the test tubes will be measured using a ruler.
Time recorded for complete reaction of substrate
(type: controlled variable)
Recording will be done only at the end, so the stopwatch is there to ensure correct timing.
Enzyme concentration (catalse)
(type: independent variable)
The food samples are made into cylinders using cork borer, therefore same diameter and each is cut 1cm long.
Substrate concentration (hydrogen peroxide)
(type: controlled variable)
Same concentration and percentage of hydrogen peroxide used.
- 5 different food samples (plant type)
- 125 cm3 Hydrogen peroxide (one typical concentration)
- 2 Stopwatch( )
- 1 Thermometer(0.5oC )
- 1 Beaker
- 2 test tube rack
- 25 test tubes
- 1 Kettle
- 1 Cutter
- 1 Marble to cut the food samples
- Aluminium foil
- 1 dropper (0.25cm3 )
- 1 measuring cylinder ( 0.2cm3)
- Ruler (0.5 mm)
- 5 petridishes
- 1 cork borer
Procedure (HINT: read through the whole procedure before starting the experiment)
1) Prepare all your materials on your work desk
2) Make a cylinder of each food sample, all of same diameter
3) Cut the cylinders into pieces of 10mm long
4) Measure 5cm3 of hydrogen peroxide and add to same amount into 5 test tubes (cover test tubes with aluminium foil
5) Place the test tubes into the a test tubes rack
6) Fill the kettle with water and turn on
7) Then pour water into a beaker to make the water bath
8) Add ice to regulate the temperature to 37oC
9) Add the food samples each into a different test tubes
10) Put the test tubes into the water bath
11) Start the stopwatch
12) After 10 minutes check your test tubes
13) After 20 minutes, remove the test tubes and place it back into the test tubes racks
14) Record the height of the foam immediately
15) Rinse all the materials that won’t be used to keep work station clean
16) Do this experiment at least 5 times to be able to calculate the mean and the standard deviation
Safety and precautions
- Wear goggles
- Handle hydrogen peroxide with care, it is harmful, corrosive and an oxidant
- Wear lab coat if provided
- Keep your station clean
- After using the apparatus, put them in the basin to be washed.
- Try not to be too close to another person’s work station
- Put all stools under the table
- Make sure there are no parallax error when reading volumes etc
- Take precaution when cutting the food samples as the cutter used is very sharp
- If help is needed, call the supervisor/teacher but do not try experimenting without knowing what is going on.
Conclusion and evaluation
Equipment used and manipulating errors
How can it be modified/improved
The food samples were cut into cylinders; therefore, the surface area to rate of reaction was not constant.
The food samples could have been crushed by pestle and mortar or even a blender. Therefore, the surface area to rate of reaction effect could be neglected.
When cutting the cylinders into 1 cm each, all cylinders were not equal as some were cut diagonally, some straight and not all were exactly 1cm.
It would have been better and more accurate if the mass of the food samples were taken using an electronic balance.
When holding the food sample with our hands, either to be cut or to put into the test tubes, this could cause delay in the reaction as we are mixing the tissues found in one food sample with other food samples
To make sure that doesn’t happen, forceps should be used to avoid the contact of food sample tissues with other tissues
The height of foam was measured with a ruler(0.5mm)
The results obtain are not accurate therefore a millimeter ruler should be used.
I created the water bath by adding boiling water in a beaker, then regulating it with ice cubes. Therefore the temperature may not have been constant throughout the experiment
Using a proper water bath, the optimum temperature for the enzyme to work could have been kept constant.
Not all the test tubes used were of the same height. This is due to lack of one type of the test tubes. To note only 20 test tubes were same, only the other 5 was different.
All the test tubes used should have been of same height, to ensure that the height of foam does not vary.
When one set of experiment is being timed for 20 minutes. I waited it to finish then starting another one.
When one set is being timed, prepare another one, ask for another stopwatch, and start to time this one as well. To note that I realized that I can do this when I was on my 3rd replication.
Not all the food samples were put at the same time as well. It must be mentioned as once the food sample is in contact with the hydrogen peroxide, they start reacting.
Unfortunately, there are no way round for this step. Therefore, the only way to make sure the data is not biased, is to be as fast as possible when putting the food samples in the test tubes containing hydrogen peroxide.
Could keep track of the pH or even make sure that it is kept constant
The only way for the pH to remain intact is to use a pH buffer.
Height of foam was used as independent variable, which can be inaccurate due to loss of oxygen molecules
A manometer could have been used to measure the oxygen released. The movement of the solution would indicate the oxygen released.
According to the figures and the graph above, it was clearly seen that potato had the highest enzyme activity than the other food samples. Therefore, it can be said that potato contains most catalase, followed by carrot, then beetroot, onion and finally apple. According to research, it was found that 37oC is the optimum temperature for the enzyme catalase in potato, therefore, it can be said that the enzyme worked at its best. According to a research the optimum activity of catalase in apple is 50oC, probably that is why the obtain result is so low but according to another research, it was found that apple is catalase activity absent like other fruits, due to their high acidity. The standard deviation for all the food samples except carrot lies within ï¿½1 S.D. This shows that the recorded values in the carrot experiment are not clustered to the mean and there are outliers in the recorded values. The highest range in height of foam is from the food sample (carrot), probably, in one of the experiment, the foil was moved, a little air space was created and the oxygen managed to escape.
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