A group of students investigated the effect of temperature on the activity of two forms of trypsin: human trypsin and icefish trypsin.
Part of their method is shown below:
- use 10cm3 of 5% trypsin solution for all trials
- measure enzyme activity at 10, 20, 30, 40 and 50°C for both enzymes
- carry out each trial in the same pH buffer
- repeat the experiment 5 times at each temperature
- measure enzyme activity by recording the area of gelatine on a photographic film that is broken down over a set time period
- calculate the rate of enzyme activity at each temperature.
(i)
Suggest and explain two improvements that would increase the validity of the students’ investigation.
Improvement .....................................................................................................................
Explanation .......................................................................................................................
Improvement .....................................................................................................................
Explanation .......................................................................................................................
[4]
(ii)
Suggest appropriate units to use to represent the rate of enzyme activity in this investigation.
[1]
(iii)
The students recorded the temperature that produced the fastest reaction rate in each of the five replicates. These results are shown in Table 3.
Replicate |
Temperature that produced the fastest reaction rate (°C) |
Human trypsin |
Icefish trypsin |
1 |
40 |
20 |
2 |
10 |
10 |
3 |
30 |
20 |
4 |
40 |
30 |
5 |
40 |
30 |
Mean = |
32.0 |
22.0 |
Mode = |
40 |
20 and 30 |
Median = |
40 |
20 |
Table 3
One of the students made the following statement:
I think the mean is a more accurate measure than the median or mode for these results.
Evaluate the student’s statement.
 [2]
(iv)
The students wanted to know whether there was a difference between the reaction rates of the two forms of trypsin at 30°C.
They performed a statistical test on the mean of the five replicates for human trypsin and the five replicates for icefish trypsin.
Suggest the most appropriate statistical test for the students to use and explain why this test is appropriate.
 [2]