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(a) Suggest why it is important that the test subjects should not know whether they are having a drink with caffeine or without caffeine.
(b) (i) State the independent variable and the two dependent variables in this investigation.
independent variable = ..................
dependent variables = ...................
(b) (ii) Use the information given to describe a method by which the student could test their hypothesis using one of the drinks.
Your method should be detailed enough for another person to follow.
(c) (i) State why Pearson’s linear correlation test is suitable for the data.
(c) (ii) The results of the statistical test gave Pearson's linear correlation, $r = -0.722$.
State what this value indicates about the relationship between the concentration of caffeine and the mean reaction time.
(c) (iii) Describe how the student calculated the degrees of freedom.
(c) (iv) Describe how the student used the probability table to find out if the value for $r = 0.722$ is significant.
(d) Suggest two reasons why the method used for the investigation into the effect of caffeine concentration may have given results that are not reliable.
(e) Effects of caffeine in the body include the promotion of acetylcholine release and the inhibition of acetylcholinesterase.
Suggest how this could account for the results in Table 1.2.
537
588
507
An investigation was carried out into the size of individuals in a species of ground beetle common in Europe. Five different sites, A to E, were sampled during the three warmest months of the year.
Table 2.1 shows information about the temperature at these sites.
[Table_1]
The population at each site was sampled a total of 10 times during the three month period.
The beetles were sampled at 20 different locations within each site, on the same day.
The length of each captured beetle was measured to the nearest mm as a measurement of body size.
The beetles were divided into two groups according to body size, large and small.
The results from the different locations in each site were added together.
The population size and the percentages of large and small beetles in the population were estimated.
(a) (i) State two variables which have been standardised in this investigation.
1 ..............................................................................................................................
...............................................................................................................................
2 ..............................................................................................................................
............................................................................................................................... [2]
(ii) Outline how the population size of the beetles can be estimated.
...............................................................................................................................
...............................................................................................................................
...............................................................................................................................
............................................................................................................................... [2]
(b) Table 2.2 shows the results of the investigation.
[Table_2]
(i) Complete Table 2.2 by filling in the missing values for sites B and C. [2]
(ii) State, with a reason, whether these results support the hypothesis:
The body size of individuals in populations of ground beetles increases as the environmental temperature decreases.
...............................................................................................................................
...............................................................................................................................
............................................................................................................................... [1]
(c) State two other conclusions that can be made about the effect of temperature on body size of the beetles.
1 ..............................................................................................................................
...............................................................................................................................
2 ..............................................................................................................................
............................................................................................................................... [2]
(d) Predict one way in which climate change may influence the populations of these ground beetles.
...............................................................................................................................
............................................................................................................................... [1]
525
567
570
