No questions found
The students thought that the area stained brown was proportional to the amylase concentration.
(a) Identify the independent and dependent variables in this investigation.
independent variable $\text{.......................................................}$
dependent variable $\text{.......................................................}$ [2]
(b) Describe how the students could use the method outlined in Fig. 1.1 to find out the concentration of the enzyme amylase in their extract.
Your method should be detailed enough for another person to follow.
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
[8]
(c) There are different types of amylase enzyme. They hydrolyse starch in different ways.
Two of these enzymes are:
\[-\beta\text{-amylase hydrolyses every second } \alpha\text{-1,4 glycosidic bond in starch molecules}\]
\[-\gamma\text{-amylase hydrolyses all } \alpha\text{-1,6 glycosidic bonds and all } \alpha\text{-1,4 glycosidic bonds in starch molecules}\]
In a second investigation, the students were provided with two beakers, A and B. One contained $\beta$-amylase and the other contained $\gamma$-amylase. They used these solutions to hydrolyse $25 \text{cm}^3$ samples of $0.5 \text{g dm}^{-3}$ starch solution. Suggest and explain how the students could identify which beaker contained $\beta$-amylase and which contained $\gamma$-amylase.
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$ [2]
(d) Humans produce the enzyme $\alpha$-amylase in their salivary glands. There may be many copies of the gene coding for $\alpha$-amylase on chromosome 1. The concentration of the $\alpha$-amylase in the saliva is positively correlated with the number of copies of this gene.
In a third investigation, the students obtained saliva from six people, A to F. Equal volumes of saliva were added to wells in agar plates similar to those shown in Fig. 1.1. The plates were incubated for the same length of time and the area of the brown zone for each sample of saliva was calculated.
Table 1.1 shows results of this investigation.
[Table_1]
(i) Identify two results in Table 1.1 that may be anomalous. Show your answers by circling the two values. [2]
(ii) State how the students should deal with these anomalies.
$\text{....................................................................................}$ [1]
(iii) The students decided to calculate the standard deviations of their results using the formula:
\[ s = \sqrt{\frac{\sum (x - \overline{x})^2}{n - 1}} \]
Key to Symbols
$s$ = standard deviation
$x$ = a result
$\overline{x}$ = mean
$\Sigma$ = sum of
$n$ = sample size
Use Table 1.2 and the formula above to calculate the standard deviation for the results for person F.
[Table_2]
answer $\text{.......................................................}$ [2]
(iv) Suggest an explanation for the results shown in Table 1.1.
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
$\text{....................................................................................}$
[3]
538
550
540
An investigation to measure the NCV in the ulnar nerve in females of different ages was carried out on 394 individuals.
(a) Suggest three variables which the investigators should have standardised. [3]
Table 2.1 shows the results of this investigation.
[Table_1]
age category / years | mean conduction velocity ± $S_M$ | confidence limits
lower limit | upper limit
30–39 | 54.3 ± 1.200 | 51.90 | 56.70
40–49 | 54.7 ± 0.645 | 53.41 | 55.99
50–59 | 52.4 ± 0.600 | 51.20 | 53.60
60–69 | 52.2 ± 0.675 |
70–79 | 49.0 ± 1.075 | 46.85 | 51.15
$$S_M = \text{standard error}$$
(b) The confidence limit = mean ± $2 \times S_M$
Use this formula to calculate the missing confidence limits. Use the space below for any working and enter your answers in Table 2.1. [1]
One conclusion from these data is that mean conduction velocity in the ulnar nerve varies significantly with age.
(c) (i) Identify two age categories which appear to support this conclusion and give a reason for your choice.
age categories ............................................................. and ....................................................
reason ......................................................................................................................................................................................... [2]
(ii) State which statistical test could have been used to confirm this conclusion and give a reason for your choice.
test ..................................................................................................................................................................................
reason ..................................................................................................................................................................................
.................................................................................................................................................................................. [2]
(iii) State a null hypothesis for this test.
..................................................................................................................................................................................
.................................................................................................................................................................................. [1]
(d) State one reason why the results of the investigation were considered to be reliable.
..................................................................................................................................................................................
.................................................................................................................................................................................. [1]
566
560
587
