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(a) (i) State two independent variables in this investigation.
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(ii) State the dependent variable in this investigation.
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(iii) Identify one variable that has been standardised in this investigation.
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(b) State a reason for each of the following procedures:
(i) using a phosphate buffer solution
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(ii) keeping the extract ice cold
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(iii) using a fine mesh to filter the extract.
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(c) (i) On Table 1.1 indicate, by placing a circle around each value, two results that may be anomalous.
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(ii) Complete Table 1.2 by calculating the rate of photosynthesis for the green and white striped leaf at a wavelength of 530 nm. Show your working.
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(d) The student analysed these results and proposed two hypotheses:
• There is a pigment in red leaves which is not present in the other leaves.
• Yellow leaves do not have a pigment that is found in the other leaves.
To test these hypotheses the student used chromatography to separate the pigments in the leaves.
(i) Outline a procedure the student could use to extract the leaf pigments and separate them by chromatography.
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(ii) Use Fig. 1.2 to describe the evidence that supports the student's hypotheses.
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523
595
584
(a) (i) Explain how the results of crosses 1 and 2 show that the allele ‘without tail’ is dominant.
(ii) Explain how the results of crosses 3 and 4 show that the gene for this condition is not sex linked.
(b) Based on the results of cross 1 in Table 2.1 a student decided that:
• the cats without tails are always heterozygous
• the ratio of their offspring ‘with tails’ and ‘without tails’ is not as expected for this type of cross.
(i) The student carried out a chi-squared test (\( \chi^2 \text{ test} \)) to determine if the offspring ratio in cross 1 differed significantly from that expected of a cross between two heterozygotes.
State one reason why the student chose this statistical test.
[1]
(ii) Complete Table 2.2 to calculate the value of \( \chi^2 \) for the results of cross 1.
The equation for the calculation of \( \chi^2 \) is:
$$\chi^2 = \sum \frac{(O-E)^2}{E} \quad O = \text{Observed result} \quad E = \text{Expected result}$$
[3]
(iii) State why the student should look for the critical value at 1 degree of freedom in this investigation.
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(iv) State the conclusion from the \( \chi^2 \) value calculated in (ii).
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(v) Cats without tails are always heterozygous for this gene. Homozygous dominant cats are never born.
Suggest what could account for the effect of the dominant allele in the homozygous condition.
[1]
570
544
596
