PREDICTION: The rate of reaction will increase as enzyme concentration increases. This means the volume of gas will increase as the number of discs in the substrate Hydrogen Peroxide increases in a limited amount of time. This will happen because there are more enzymes present, therefore a bigger, quicker reaction will incur because there are more collisions able to happen between the enzymes and substrate, therefore producing more energy and the activation energy will decrease (see fig 2). Consequently , more products being produced in less time. Eventually hydrogen peroxide would produce oxygen and water on its own, producing the same amount of oxygen as with a catalase, the catalase just speeds the reaction up! Therefore the prediction is if that if double the amount of enzyme if used then the reaction rate is doubled therefore oxygen will be produced twice as fast.
VARIABLES:
Variables which could affect any outcomes or results are o be suitably controlled. Only enzyme concentration will be varied. Substrate concentration, pH and temperature will be kept constant.
Temperature:
As it rises, molecules move faster due thermal energy changing into kinetic – this increases the rate at which the enzyme and substrate molecules come into contact, therefore products are formed more rapidly. However if too high temperatures disrupt the molecular structure – the hydrogen and ionic bonds are broken and the enzyme is denatured. To control this a thermometer was used to keep a constant 22C.
Substrate concentration:
An increase in substrate concentration produces an increase in rate of reaction. But if there are sufficient substrate molecules to enzymes, the rate is unaffected. To control these, identical quantities of 100ml of hydrogen peroxide was used each time. Measuring cylinders were used to provide total accuracy.
PH:
A change in pH can affect the ionic and hydrogen bonding-it alters the shape of the enzyme. An enzyme has an optimum pH where the active site best fits the substrate. A change can denature or slow the reaction of an enzyme. PH happened to be at 5.0 in the pilot test, so this was monitored throughout to make sure it did not change. However a pH buffer could be used to maintain a certain pH, perhaps 7.0 which is neutral as most enzymes have 7.0 as their optimum pH.
Prior to this plan I performed a pilot test to investigate which volumes would be most suitable and best to achieve optimum results. It was found that 100ml of hydrogen peroxide was best and that starting off with 10 discs and progressing up in five, performed best.
PH was kept at a constant 5.0 and temperature controlled at 22C. I incurred the following results:
10 discs – 5ml of oxygen
15 discs – 6.5ml of oxygen
20 discs – 7.5ml of oxygen
25 discs – 10ml of oxygen
30 discs – 14ml of oxygen
Discs were kept at 5mm in diameter and 2mm in width to control surface area as enzymes on the surface only work on the substrate H2O2.
∙ I am not counting the number of bubbles produced, as this is a very inaccurate way to measure the rate of reaction. I will be using a gas burette instead. A syringe was considered but, as found in the pilot test, the volume of the gas burette would not be large enough even though the measurements are slightly more accurate than the gas syringe. Boss and Clamp are also being used to ensure experiment can be monitored safely and to protect the enzyme substrate solution from unnecessary shaking, as this could be unfair.
EQUIPMENT:
Boss clamp Hydrogen peroxide
Ceramic tile Goggles
Scalpel Gloves
Ruler Gas syringe
Stopwatch Measuring cylinder
Universal indicator Conical flask
pH chart
Potato
METHOD:
- With a cork borer (5mm diameter), cut enough cylinders from potato tissue to be able to cut 110, 2mm thick discs. Then place them under water in petri dish.
- Arrange apparatus with 100ml of hydrogen peroxide in the conical flask. Wear eye protection, as H2O2 is corrosive. Also add three drops of universal indicator and measure the temperature of the fluid to make sure the pH and temperature stay constant throughout the experiment.
- Making sure the gas syringe is at 0ml, add 10 potato discs and replace the bung immediately, making sure it provides an air tight seal, and note the time.
- Gently shake the conical flask. As the reaction begins and oxygen is produced, you should see the gas syringe slowly extending because of the pressure of the gas that is being produced. After 4 minutes has passed record the level of the gas syringe, pH and temperature to check they have stayed constant and fair.
- Remove the bung and thoroughly wash out flask.
- Now carry out 4 further tests each with a fresh set ascending 15, 20, 25 and 30 discs. Follow the same procedure. Carry out the entire test another two times as the averages can be taken therefore recordings are more accurate. Odd results can also be spotted.
SAFENESS: Gloves should be worn, as H2O2 is corrosive. Also goggles to protect eyes. Extra care should be taken when the scalpel is in use. Tie hair back and stow away belongings.
SURFACE AREA:
The total surface area of the potato discs could be considered. In analysis and results it would be useful to find any patterns or trends with the relationship between the surface area and amount of products produced.
A formula used to find the surface area of one disc:
h(πd) + 2(πr ) r = radius
d = diameter
h = height
For one disc:
r = 2.5mm
d = 5.0mm
h = 2.0mm
2( π x 5 ) + ( π x 2.5 ) = 70.7mm
The concentration of enzyme is going to be varied by changing the surface area of potato exposed to the hydrogen peroxide. This is because the enzymes in the middle of the disc are inactive, as they do not come into contact with the substrate, therefore only the enzymes on the surface react.
Blank table of how results will be displayed
