AS & A Level Biology - 9700 Paper 5 2017 Summer Zone 2

Fig. 1.1 shows an aquatic crustacean belonging to the genus Daphnia. These animals usually measure between 1–5mm in length. They have a two-chambered heart which can be seen through the exoskeleton when viewed using a low-powered microscope.

A biology teacher told a class that caffeine can temporarily relieve tiredness in people by increasing heart rate. Table 1.1 shows the caffeine content of various products.
[Table_1]
One group of students in the class used Daphnia to test the hypothesis:
Heart rate increases when caffeine concentration increases.
(a) Identify the independent and dependent variable in this investigation.
independent ..............................................................................................................................
dependent ..................................................................................................................................
[2]
(b) (i) Describe a procedure that the students should use to prepare the 100mg dm^–3 caffeine solution.
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[2]
A culture of healthy Daphnia was supplied to the students in a tank containing fresh water and a suitable food source.
Each student followed the same basic procedure.
• A Daphnia was placed on some cotton wool fibres in a cavity microscope slide as shown in Fig. 1.2.
• A few drops of 100mg dm^–3 caffeine solution were immediately added to the slide.
• The Daphnia was observed using the low power objective lens of a microscope.
• The number of heart beats of the Daphnia was counted.

(ii) Suggest one reason why the Daphnia was placed on cotton wool fibres.
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[1]
(iii) The students decided to adapt their basic procedure to test their hypothesis that:
Heart rate increases when caffeine concentration increases.
Describe a method which the students could use to test this hypothesis. Your method should be detailed enough for another person to follow.
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[6]
(iv) Suggest one feature of the procedure which may have added a source of error and suggest how the students could have reduced its effect.
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[2]
The data the students obtained showed that as the concentration of caffeine increased, the heart rate of the Daphnia also increased.
The students concluded:
To relieve tiredness, people should increase their caffeine intake so that their heart rate will increase.
(c) Suggest why the students’ conclusion was not valid.
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[1]
Another group of students decided to use cola as their source of caffeine. They diluted the cola to give a range of caffeine concentrations. They counted the heart rates of Daphnia in each of these concentrations.
Table 1.2 shows their results.
[Table_2]
(d) (i) On Table 1.2 indicate, by placing a circle around the value, one result that may be anomalous.
[1]
These students concluded that:
The heart rate of Daphnia increased proportionally to the concentration of caffeine.
(ii) Suggest two reasons why the data collected was not sufficient to make this conclusion.
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[2]

Some populations of white clover, _Trifolium repens_, are described as cyanogenic because they produce hydrogen cyanide.
Hydrogen cyanide is a poison which inhibits respiration and reduces grazing by herbivores.
A group of scientists investigated the percentage of cyanogenic plants in populations of _T. repens_ growing in different locations. The mean January temperature was also recorded.
Table 2.1 shows the results of their investigation.

[Table_1]

The scientists calculated the Spearman's rank correlation coefficient to test the hypothesis:

The proportion of cyanogenic plants in populations of _T. repens_ increases as the mean January temperature increases.

(a) State a null hypothesis for this test.
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............................................................................................................................ [1]

(b) The formula for Spearman's rank correlation is
$$r_s = 1 - \left( \frac{6 \times \Sigma D^2}{n^3 - n} \right)$$ where
n = number of pairs of items in the sample
D = difference between each pair of ranked measurements

(i) Complete Table 2.2 to show how the values for $D^2$ were calculated. [2]
[Table_2]

(ii) Complete the steps of the calculation to find the value of $r_s$. Give your answer to two decimal places.
$$r_s = 1 - \left( \frac{6 \times 14}{3 - ........} \right)$$
$$r_s = 1 - \left( \frac{84}{........} \right)$$
$$r_s = 1 - ........$$
$$r_s = ........................................................ (2 \text{ d.p.})$$ [2]

Table 2.3 shows the critical values of $r_s$ at the 0.05 probability level.
[Table_3]

(iii) Explain why the scientists rejected the null hypothesis.
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............................................................................................................................ [1]

(iv) Suggest why there is a higher proportion of cyanogenic clover plants at locations with high mean January temperatures compared with the other locations studied.
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............................................................................................................................ [1]

An investigation was carried out into the population of a species of vole in one area of the USA. The population was sampled during the first two weeks of August between 1983 and 2004. Traps for catching small mammals were placed at equal distances along the same parallel line transects. Each year, the number of voles caught per 1000 traps was recorded.

Fig. 3.1 shows the results.



(a) Identify three ways in which this investigation has been standardised.
1 ..............................................................................................................................................................................................................................................................................................
2 ..............................................................................................................................................................................................................................................................................................
3 ..............................................................................................................................................................................................................................................................................................
[3]

(b) Over the period of the study, it was found that 8 out of every 50 voles in this population had black fur, whilst all the other voles had brown fur.

Fur colour in voles is controlled by a single gene, \( A/a \). Voles with black fur have the genotype \( aa \).

The Hardy-Weinberg principle states that:
$$p+q=1$$
$$p^2+2pq+q^2=1$$
\( p \) = the frequency of the dominant allele
\( q \) = the frequency of the recessive allele

Use the Hardy-Weinberg principle to calculate the expected number of voles heterozygous for fur colour that were recorded in 1997.
Give your answer to the nearest whole number.

number of voles per 1000 traps which are heterozygous for brown fur in 1997 = .................[3]