2H2O2 O2 + 2H2O
There are 6 main factors that affect enzymes. They are:
- Temperature: [Amylase is an enzyme which breaks down starch into sugar (maltose).]
- pH: This is to test at which pH did the enzyme, amylase, work most rapidly and what the optimum temperature was.
- Surface Area: If there are more wider potato samples, then the surface area would be greater, and therefore the reaction would take place much quicker.
- Pressure
- Concentration of the enzyme: If the concentration of the enzyme is great, then the reaction would be much quicker.
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Concentration of the substrate: If the concentration of the substrate is great, then the reaction would take longer to completely break down – also you may see an increase in rate however.
I have chosen to test the temperature. (This is because, the temperature is always present in all tests and gives the greatest variety and fairest results out of the other tests.)
The above 6 factors affect the enzyme in their own different ways. As the temperature gives the most reliable sets of results, it is the best one to pick to get the most accurate results.
Is it a fair test? How?
This will be a fair test as all of the test tubes will be in the water baths at constant temperatures. This would mean that they are all under the same constant conditions. The concentration of the substrate will stay the same however, so there will be no bias.
To ensure that the experiment is a fair test and that the results are accurate the concentration, pressure, surface are and pH will be kept constant so that they do not affect the results.
To keep the concentration of the enzyme constant through the all the experiments they will not be diluted they will be left at 100 percent concentrated. This will ensure the concentration will not affect the rate of reaction, as the concentration will be kept constant through all the reactions so this will not affect the overall results of the experiment. This will mean that the same number of particles of the enzyme and the substrate will be very experiment so this will not be a factor in the experiment as it will be constant in all the experiments.
To keep the pressure constant during all of the experiments the reaction will be undertaken at lab pressure for all the experiments. This will mean that during all the experiments in which the reaction will take place will be the same so this will not be a factor as the particles will have the same area in which to react in, in all of the experiments. This will ensure that pressure is not a factor in the reaction so the results are accurate, as only one of the five factors is being altered not more than one.
To keep the surface area constant during the reaction the same number of potato chips will be placed in the reaction every time. There will only be one potato chip in each boiling-tube. This will ensure that this will not be the factor during the experiment; as the surface area is increased, the rate of reaction increases. This is because the enzyme has a greater area upon which it can react, so the will be much faster. To keep the experiment a fair test, this will have to be kept constant though all the experiments will ensure that the results are accurate.
To keep the pH constant it will not be altered during the experiment. The pH will be neither acidic nor alkaline, as the experiment will occur while the pH is neutral. This will not mean that the pH will not affect the experiment, although the enzyme is pH specific this will not affect the experiment, as the reaction is neither acidic nor alkaline so the pH will not be effect the rate of reaction. This will mean that the results will not be affected by this variable as it is going to be kept constant.
The optimum temperature does not have to be 37°C, as the reaction s not taking place inside a warm-blooded animal, the maximum temperature does not need to be 37°C. there is an optimum temperature, although we are not sure what it is exactly. As we are using potato instead of liver, the optimum temperature would be 37°C, but not for the potato.
What are molecules doing at such a low temperature?
(Practical theory)
Collision Theory: The higher the temperature the more the molecules can move about and the more often they can. Therefore, more successful collisions take place and results in a higher rate of reaction.
Reactions in which large molecules are built up from smaller molecules are called anabolic reactions (as shown below) – a ‘building up’ reaction (anabolic)
Enzymes fit exactly with its substrate (the molecule it acts on). They have to fit together for them to work.
Too much energy will deform the enzyme. Things like high temperatures and extreme pH’s will cause this. At one point, the enzyme will cease to work.
The various factors will effect the reaction in different ways and will give different results.
The temperature results, when plotted, would give a graph like…
Before the optimum temperature is reached, the rate increases as the temperature rises, but at the optimum temperature, the enzyme de-forms. This means that the rate of reaction stops. This is why the line after the optimum is a straight line down.
The pH results, when plotted, would give a graph like…
In the same way as before, after the optimum temperature is reached the enzymes stop working and there is no more ‘rate of reaction’.
The concentration results, when plotted, would give a graph like…
The pH optimum of the different enzymes should normally be pH7; although there are a few exceptions, like pepsin. It has a pH of around 2 or 2.5. But, most enzymes have the neutral pH.
To test for the pH, you would need ‘buffers’ to control the pH levels. This would be difficult for us to do, as we do not have the equipment. Although you could use universal indicator paper; but using this, you can see the change only, therefore assume no change.
Pressure will change normally in controlled conditions, but as we are doing this experiment at atmospheric pressure, the pressure will stay the same.
The concentration of enzyme is the number of potato chips. It is the potato chips, because that is where the enzymes are. The more potato chips in the boiling tube, the greater the concentration of the enzyme.
The concentration is how many chips needed to get the best results.
When testing temperature, it is likely to get very good, clear results.
In a highly concentrated H2O2 solution the number of H2O2 molecules is high, therefore the chances of a H2O2 colliding with a catalase enzyme would be greater. This in turn increases the rate of reaction, i.e. more water molecules and oxygen is produced.
When the concentration is lowered, the rate of reaction in turn is lowered as the number of collisions decrease due to the diminished number of H2O2 molecules.
Prediction
I believe and predict that as the temperature increases, the rate of reaction will also increase. This means that the higher the temperature at which the reaction takes place, the faster the rate will be. But the is a negative side. At one point, when the temperature is too high, the enzyme will deform. This would mean that after the enzyme has deformed, it would not work. The temperature at which this happens is called the optimum temperature. In the experiment, as I go along, I will be able to see what the optimum temperature is.
I think this due to the backing evidence of collision theory, which states the following facts:
- Reactions occur due to the collision of reactant particles
- A collision only results in a reaction if a certain minimum energy is exceeded
- A collision will not result in a reaction unless the colliding particles are correctly oriented to one another
As the temperature increases, this gives the particles extra energy. This means that they will be moving around much quicker, thus the change for a successful collision increases, meaning that the rate of the reaction will also increase. This will mean that as the temperature increases, the rate of the reaction will also increase leading to a quicker reaction. But as the optimum temperature is reached the enzyme will denature, thus meaning that it will no longer react with the substrate as the enzyme will no longer be the same shape meaning that it will no longer fit perfectly with the substrate leading to no reaction what-so-ever between the enzyme and the substrate. This means that when the optimum temperature is reached and the enzyme denatures the reaction will no longer occur and the rate of the reaction will stop completely as the reaction is no longer taking place.
How did you do this to decide what to control and how?
- Need to use a water bath
- The temperature of the water bath measured using a thermometer
- The room temperature part of the experiment, only needing for the boiling-tube to be place in a beaker filled with tap water, as a heated water bath is not necessary.
- Thermostatically controlled water baths – heated water baths
What should happen?
Safety Precautions
Hydrogen peroxide is corrosive.
Corrosive: Any solution equal to or stronger than 5.9M (i.e., 20% or 71 ‘vol’) is CORROSIVE and causes burns. Solutions stronger than or equal to 1.5M (i.e., 5% or 18 ‘vol’) but less than 5.9M are IRRITANTS to the eyes and skin.
Dangerous With: ORGANIC COMPOUNDS such as propanone, ethanol, glycerol, and many others. Dangerous or explosive reactions can occur.
METALS AND METAL OXIDES (especially if finely divided) and TIN(II)CHLORIDE. Violent decomposition of hydrogen peroxide takes place.
DANGEROUS IF SWALLOWED. Causes serious internal damage due to release of oxygen.
If swallowed: Wash out moth and give a glass or two of water. Seek medical attention as soon as possible.
If liquid gets in eyes: Flood the eye with gently running tap water for 10 minutes. Seek medical attention.
If spilt on skin or clothes: Flood area with large quantities of water. Remove contaminated clothing and soak. If a large area is affected or blistering occurs, seek medical attention.
If spilt in laboratory: Wear eye protection and gloves. Cover the mineral absorbent and clear up into a bucket. Rinse several times. Add water to dilute at least ten times before washing the liquid down the foul-water drain. The absorbent may go in the refuse.
Apparatus
- 1 large potato
- 1 borer
- 1 scalpel
- Marker pen
- 5 boiling-tubes
- Measuring cylinder
- Delivery tube with bung
- Stop-watch
- Water
- 100cm³ of hydrogen peroxide solution
- Thermometer
- Stopwatch
Method
- Get a potato and using a borer, cut out 5 sample of potato, all of the same size.
- Place 10cm³ of hydrogen peroxide solution in each of the five boiling tubes labeled 1, 2, 3, 4 and 5.
- Prepare 5 water-baths at the following temperatures:
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Room temperature – 17°C→ 22°C
- Water bath set at 30°C
- Water bath set at 40°C
- Water bath set at 50°C
- Water bath set at 60°C
- Set up the apparatus with the measuring cylinder upside down, filled with water in a container full of water.
- Connect the delivery tube underneath the measuring cylinder in the water.
- Place tube 1 into the room temperature water-bath, tube 2 into the 30°C water-bath, tube 3 into the 40°C water-bath, and so on.
- Leave them in their own baths for 5 minutes till they reach the temperature of the water-bath.
- Read the temperature of the water-bath, as it is not always exact to the nearest 10°C.
- After 5 minutes, add the potato sample to the tube with the hydrogen peroxide, and cover it with the bung connected to the delivery tube. Start measuring the rate at which the reaction takes place.
- Note down the results.
- Repeat for each of the other boiling tubes in the different water baths.
Diagrams
Results
I was not able to obtain many results but I did get these following ones:
(I have drawn graphs for these results to show the increase in rate and to show what happened as the reaction took place.)
