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(a) (i) Identify the independent and dependent variables in this investigation.
independent variable ............................................................
dependent variable ............................................................
(a) (ii) State the variable being controlled by the use of plastic bags.
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(b) (i) Suggest a method by which the student could have obtained and transferred the pollen from species B to species A.
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(b) (ii) Identify one potential safety issue with the experimental method you have described.
State a suitable precaution.
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(c) The fruits of the grass species used by the student are similar in structure to maize fruits.
In steps 6 and 7 the student collected the fruits formed by species A in order to count the chromosomes in the cells of the embryos.
Suggest a procedure by which the student could:
• obtain cells of the embryo plant in which chromosomes would be present
• make the chromosomes visible so that they could be counted.
Outline the main stages of this procedure.
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(d) Table 1.1 shows the results that the student obtained from the investigation.
\[ \text{Table 1.1} \]
\[ \begin{array}{|c|c|} \hline \text{number of chromosomes in the embryo plants} & \text{hybrid of species A and species B} & \text{hybrid of species A and species C} \\ \hline 16 & 26 \\ \hline \end{array} \]
Explain the results of the student’s investigation as shown in Table 1.1.
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(e) (i) The student also counted the number of chromosomes in the female gametes of each hybrid.
Predict the number of chromosomes you would expect the student to find in the female gametes of each hybrid.
hybrid from the cross A × B ........................................................
hybrid from the cross A × C ........................................................
(e) (ii) State the evidence in Table 1.2 that supports this conclusion.
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(f) (i) Complete Table 1.3 by writing in the values of the mean, mode and median for the hybrid from the cross of A × C.
\[ \text{mean} = 34 \quad \text{mode} = 34 \quad \text{median} = 34 \]
The student recorded the calculations for the hybrid from the cross of A × B in Table 1.3.
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(f) (ii) State a reason why the student used the \textit{t}-test to find out if the difference in germination of the two hybrids was significant.
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(f) (iii) State a null hypothesis for this test.
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(f) (iv) State why the student used 20 degrees of freedom for this test.
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502
532
573
The effect of temperature on the permeability of cell membranes was investigated using discs of a plant tissue. When discs of this plant tissue were placed in water, chloride ions were released from the cell vacuoles.
Discs of this plant tissue were placed in tubes of deionised water in water baths at different temperatures for 30 minutes as shown in Fig. 2.1.
The concentration of chloride ions in the water around the plant tissue was measured using an ion-sensitive electrode.
(a) (i) State how three different variables have been standardised in this investigation.
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2. .................................................................
3. ................................................................. [3]
(ii) Suggest how the reliability of the results could be improved.
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(b) The results of this investigation are shown in Fig. 2.2.
(i) State how the rate of release of chloride ions is calculated for each temperature.
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(ii) Calculate the relative increase in the rate of release of chloride ions between 50 °C and 60 °C. Show your working.
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(c) The investigation was repeated, but a solution of 70% ethanol was added to each tube instead of deionised water.
Predict the effect of using ethanol on the rate of release of chloride ions from the discs in all the tubes.
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587
575
560
