(Diagram below explains the active site of an enzyme)
At the end of the reaction the enzyme remains unchanged and the product(s) leave the active site as they no longer posses the active site’s complimentary shape.
Many biological reactions produce hydrogen peroxide; hydrogen peroxide is very harmful to cells. The cells counter the hydrogen peroxide by using an enzyme called Catalase which decomposes the hydrogen peroxide into much safer products,
Catalase possesses an active site with a shape that fits the shape of the hydrogen peroxide molecule; this enables the Catalase enzyme to decompose the hydrogen peroxide faster.
In order to investigate the effect of surface area on Catalase activity I will measure the amount of oxygen released during each reaction; as the amount of oxygen indicates the rate of reaction, a higher amount of oxygen means a higher rate of reaction.
Measuring Method
There are a number of ways to measure the oxygen released in this experiment. A basic method, is counting the number of bubbles released from the reaction; this is not very accurate as the volume of the bubbles released is unknown. Another method which will be used in the experiment is to measure the volume of oxygen released from the downward displacement of water. This method is much more accurate as the readings will show the actual volume of oxygen released during the reaction.
Controls
Temperature – an increase of temperature will increase the rate of reaction until the optimum temperature of the enzyme is reached. Temperature increases the kinetic energy of the reacting particles, this extra energy creates more successful collisions between the reacting particles thus increasing the rate of reaction. But as the enzyme holds a specific three-dimensional shape, too much heat can distort the hydrogen bonds in the enzyme particle structure and cause the enzyme to become denatured; when an enzyme becomes denatured it no longer possesses its catalytic abilities.
When performing the experiment the reactions of the different surface areas are to be performed in the same temperature to avoid anomalous results. I will use the room temperature for all the reactions; preliminary experiments show reactions occurring under room temperature conditions, this means room temperature will not denature the enzyme and will contribute into providing a reliable set of results.
pH – an increase or decrease of the pH level of hydrogen peroxide will also denature the enzyme Catalase. A decrease of pH will cause the H+ ions in the enzyme particle to become attracted to the abundant negatively charged ions in the enzyme; this will change the shape of the enzyme causing it to become denatured.
There will be no change of the pH level of hydrogen peroxide throughout the experiment as changing the pH level will disrupt the rate of reaction and cause anomalous readings.
Concentration of catalase – the concentration of the catalase will be kept the same for all the reactions. Increasing the concentration increases the number of Catalase particles present in the given volume, the increase in enzyme particles will increase the probability of reacting particles to collide and thus creating a higher rate of reaction. A cork borer will be used to obtain a tube of potato with a diameter of 2cm, this will then be cut to produce a 5cm tube. The total area of the potato will be kept as a 5cm tube with a diameter of 2cm throughout the experiment; this controls the volume of the catalase to be equal for all the different surface areas.
Concentration of substrate – increasing the concentration of hydrogen peroxide will increase the rate of reaction, an increase in concentration also increases the number of hydrogen peroxide particles present in the given volume; this will create a higher frequency of successful collisions and a higher rate of reaction. To ensure the factor of an increased substrate concentration does not affect the investigation the same volume and concentration of hydrogen peroxide will be used; a volume of 20cm³ and a concentration of 0.1 M of hydrogen peroxide.
Mass of potato tissue – the mass of the potato cylinders used is another factor which affects the reliability of the results. As the surface area of the potato is increased the mass of the potato will decrease. The larger surface area created while cutting the potato allows water to evaporate more easily, also the different regions of the potato may also differ in mass. This factor cannot be controlled and will be taken into account when results are obtained.
Apparatus
potato
2cm diameter cork borer
0.1M hydrogen peroxide
10 cm³ measuring cylinder
boiling tube
scalpel
delivery tube
rubber bung
tile
stopwatch
water container
10 cm³ syringe
test tube rack
ruler
Method
1. Using the cork borer, obtain a cylinder of potato a. Remove the cylinder from the cork borer, using the flat end of a pencil to push it out .
2. Place the potato cylinder on the tile and, using the scalpel and the aid of a ruler cut off both ends, ensuring that the remaining cylinder is 5 cm’s long. Wash the cylinder briefly (do not keep in water for too long) in water.
3. Using the syringe, measure out 20 cm³ of 0.1M hydrogen peroxide into the boiling tube.
4. Fill the water container and measuring cylinder with water. The measuring cylinder should be held upside down, with the end of the delivery tube positioned in the open end of the cylinder.
5. Place the potato into the boiling tube, then quickly, holding the delivery tube push the bung into the top of the boiling tube.
6. Start the stop watch and collect oxygen for five minutes. Record the amount of oxygen released at the end of the 5minute timing.
7. Discard the contents of the boiling tube.
8. Repeat the experiment using the other potato’s with surface area variations.
9. When results for all of these combinations of cylinders have been obtained, repeat procedures 1-8 again to obtain a second set of results; to be used in obtaining an average set of results.
Number and Range
Health and Safety Regulations
Hydrogen peroxide is corrosive and can cause damage if it enters the eye, to eliminate this risk occurring when performing the investigation safety goggles should be worn throughout the experiment.
The cork borer being used can also cause damage to the body. When using the cork borer remember to keep hands away from the area of exit of the cork borer.
The scalpel must be used carefully on the white tile. Also all glassware used in the experiment should be handled with care.
