Apparatus: -Boiling Tubes
-Measuring Cylinder
-Dimple Tray
-Stirring Rod
-Stop Watch
-Water Bath
-Beaker
-Bunsen Burner
-Tri Pod
-Heat Proof Mat
-Gauze
-Thermometer
Chemicals: -Starch (2%)
-Amylase (0.1%)
-Iodine
Method:
Set up the equipment as shown above in diagram. Heat the water bath to 40ºC. Place the boiling tubes containing starch and amylase into the water bath. When the starch and amylase reach 40ºC pour both into the same tube and shake. Start the stopwatch. Dip the stirring rod into the solution and then into the first hole of iodine. Wipe the rod. In 30 seconds re dip into the solution and then into the second hole of iodine. Continue to do this every 30 seconds until the iodine stops changing colour. Record the time. Repeat 2 more times and take an average to try to minimise errors. Do the same but with the water bath at 20, 30, 50, 60 and 70ºC. Clean and use the same equipment throughout to help make it a fair test.
Prediction:
I predict that as the temperature increases the reaction will speed up. The higher the temperature the faster the reaction occurs. This means in the experiment, the higher the temperature in the water bath the less time it will take for the solution to stop changing the iodine’s colour.
This is because it is the starch in the solution that turns the iodine darker. All the starch needs to go for the iodine to stop changing colour. The enzyme amylase breaks down the starch and turns it into another substance. But for the amylase to react and breakdown the starch it must collide with it and join on to it. They fit together like a lock and key, which means that only the right enzyme can fit and break the substance down.
As amylase is the right enzyme to breakdown starch they fit together perfectly. When they lock together amylase breaks the bonds and splits the starch into smaller pieces creating a new substance called maltose. The maltose doesn’t change the iodine’s colour. When the iodine remains the same colour it means that there is no more starch left in the solution and so the reaction is completely over.
The higher the temperature, the faster the enzymes move about. The faster they are going the more chance there is for them to collide. As they collide more often then they join more often and breakdown the starch faster, causing the reaction to go faster and take less time.
I also predict that after 40°C the rate of reaction will start to slow down. As the temperature increases above 40°C the reaction will slow down. So the reaction will occur quickest at 40°C.
This is because above a certain temperature the enzyme begins to become denatured. This means the enzyme loses its shape. As they fit together tightly it means they can’t join, instead they just bounce apart. If they can’t join then the enzyme can’t breakdown the food substance.
So if some of the amylase gets denatured and can’t breakdown the starch then there is less chance of a good amylase molecule hitting the starch. This means it takes more time to breakdown the starch causing the reaction to go slower and take longer. Above a certain temperature all the amylase would be denatured, meaning no starch would get broken down at all and so the reaction will never finish.
I have said above 40°C because that is the approximate temperature that the amylase would work at inside the human body. So that should be the most effective temperature.
I predict the graph will look like this.
Results:
Analysis:
My prediction was correct. As the temperature increased the reaction took less time. My graph has the predicted shape and shows a positive correlation. However the second part of my prediction was incorrect. After 40°C the reaction did not slow down. This is because it is bacterial amylase we used in the experiment. Bacterial amylase works at a different temperature to the amylase inside the human intestine, which is what I predicted for. This is why the reactions are still increasing in speed, up to 70°C.
Too find the temperature at which bacterial amylase actually works fastest I repeated the experiment at 80°C and 90°C. These were my results:
This shows that bacterial amylase actually works quickest at 70 °C, as after that temperature the reaction slowed down. By 90°C the enzyme was so denatured that it couldn’t break down the starch at all.
Evaluation:
My results were fairly accurate and the procedure was reasonably reliable.
