Hazards
The main risk is irritation caused by exposure to iodine which could cause injury by entering the eye. The likelihood of this occurring can be reduced by wearing safety goggles.
Other hazards are:
- Risk of electrocution if water comes in contact with the electrical components of the thermostatic waterbaths
- Irritation to skin or eyes if iodine solution is spilt on them
- Allergic reaction to starch solution or enzyme.
- Glassware breakage leading to cuts
spectacles during the experiment.
Trends
At 23 OC (room temp) it took a long time for amylase to hydrolyse starch (mean = 6.7 minutes). As temperature rose to 30OC and 60OC the time taken for the amylase to hydrolyse the starch decreased from 5.7 mins to 3.0 mins. At 70 OC the reaction slowed slightly to 5.0 mins.
Reliability
The result for 60OC is very reliable as there is no range bar as all 3 results were 3 minutes. The result for 70 OC was very unreliable as the range bar is large with a range of results of 2 minutes.
Accuracy and Improvements
- There are major problems with accuracy when using this technique. The solutions are only tested every minute, hence the exact time at which starch disappears from a tube cannot be determined. This could be improved by taking a reading every 30 seconds.
- As small particles of starch produce tiny traces of purple in the midst of yellow / brown iodine, the end-point is very subjective. Different people would regard a trace of starch remaining as being a positive or a negative result. This could be improved by colorimeter to measure the % absorbancy.
-
It is hard to judge where the optimum temperature is as the intervals between the temperatures is too large. To improve this more intermediate temperatures are needed, particularly where the graph troughs and then increases. Perhaps take readings every 2.5oC between 60 and 70.
Explanation
At low temperatures, eg 23oC (room temperature), the starch and amylase molecules have little kinetic energy (they are moving slowly). Amylase’s specific active sites will not collide with their complementary substrate( starch) very often and so few E-S complexes will form. This will result in slow hydrolysis of starch.
As the temperature increases from 30 oC to 60 oC, the amylase and starch molecules move faster and hence will collide more often and with greater kinetic energy to help overcome the activation energy. These factors combine decrease the time it takes for the amylase to hydrolyse the starch into maltose. At an optimum temperature (somewhere close to 60oC from these results), the specific shape of the active site is the best fit for the complementary substrate (starch) and the time taken for the amylase to hydrolyse the starch is the quickest.
At temperatures slightly higher than optimum (60oC to 70 oC from these results), the time taken for the amylase to hydrolyse the starch increases. This is because above the optimum temperature the increasing vibration of the enzymes causes the hydrogen bonds to begin to break. This changes the specific shape of the enzyme and the specific shape of the active site. Therefore the substrate is no longer complementary to the active site. Less/ no enzyme substrate complexes form and therefore less/ no products are formed. The enzymes are being to denature.
Conclusion –
My prediction that as temperature increases(IV), the time taken for amylase to hydrolyse starch to maltose will decrease (DV). This will be until an optimum temperature of around 60OC is reached, beyond this temperature I expect the time taken for amylase to hydrolyse starch to maltose will increase appears to be correct. The wide spread of results around some of the means indicate that further experiments are needed before a more definite conclusion may be made.
