2. pH Conditions
All enzymes have an optimum pH value. Most work best at neutral pH 7, however there are certain exceptions. Enzymes in our stomach work best in acidic conditions. By altering the optimum pH the H+ and OH-ions found in acids and alkalis can mess up the ionic bonds that hold the tertiary structure in place. This makes the active site change shape, so the enzyme is denatured and it is therefore no longer able to be used.
3. Temperature Conditions
More heat means more kinetic energy, so molecules move faster. This makes the enzyme more likely to collide with the substrate. But, of the temperature increases beyond a certain point the rate of reaction decreases and ultimately stops. If the temperature goes above a certain point the vibrating enzymes break some of the bonds which are holding them together. The active site changes shape and the enzyme and substrate no longer fit together. At this point the enzyme is denatured and can no longer carry out is function.
4. Substrate Concentration
Substrate concentration affects the rate
I intend to investigate the effects on the rate of reaction upon altering the concentration of the substrate. In order to do this while also ensuring a fair test. I will aim to maintain all other variables constant.
Prediction:
Apparatus:
Boiling Tube
Rubber Bung and Delivery Tube
Potato Samples each of 10cm in length
Hydrogen Peroxide Solution
Distilled Water
Digital Stop Clock
Scalpel
Plastic Ruler
Measuring Cylinder
Water Bath set at 40Oc
Method:
1. Measure the hydrogen peroxide and distilled water for each solution using a measuring cylinder and pour into each boiling tube. This should give a decent range and adequate repeats to come to a conclusion. I decided that boiling tubes are the easiest way to keep the solutions as they can be labelled easily and can be kept in a rack till use. Although only slowly, hydrogen peroxide decays in the absence of a catalyst this may affect the results.
2. Collect the samples of potatoes and check whether they are 10cm in length, then cut each potato sample into 0.5cm intervals using the scalpel and the ruler. It is important that the potato samples are cut into intervals as it increases the surface.
3. Firstly, take Solution A and check its temperature. Once it reaches 40oC add the pieces of potato into the boiling tube.
4. Put the end of the delivery tube into a gas syringe. Measure the amount of gas produced over a five minute duration.
5. Repeat the procedure with the other hydrogen peroxide solutions.
6. Repeat all the tests at least three times so that an average can be obtained.
Table of Results:
Volume of Hydrogen Peroxide Volume of Water Volume of Oxygen produced per 5 minutes Average Oxygen produced in 1 min
1 2 3 Average
Solution A 20 0 13 13 13 13 2.6
Solution B 15 5 12 10.5 11 11.1 2.22
Solution C 10 10 11 9 10 10 2
Solution D 5 15 4 6 4.5 4.8 0.96
Solution E 0 20 0 0 0 0 0
Graph:
Analysis of Graph
The overall trend represented by the graph suggests that as the concentration of the substrate is increased there is a gradual increase in the amount of oxygen which is produced. There is a steady increase in the rate of reaction because there are more substrate molecules available. Due to the increased chnace of a successful collsion caused by random thermal motion when there are more molecules present there is an increase in rate with higher substrate molecules present, there is an increase in rate with higher substrate concentration. For lower concentrations the rate of reaction is therefore directly proportional to the concentration of hydrogen peroxide in the solution. This is because if we double the amounts of substrate molecules that are in the solution, double the amount will find an enzyme molecule at the same time if all the substrate molecules are moving at relatively the same pace.
Evaluation of Evidence
Accuracy
Although the results have validated a satisfactory graph of rate against concentration, and established a conclusion that is acceptable, the results were obviously not perfect.
Anomalies
Improvements
Although the procedure used was up to satisfactory standards, there were a number of improvements and chnages that could have been done in order to further improve the accuracy of the entire investigation.
