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(a) (i) Describe how the student could make 1 \text{dm}^3 of 0.15 \text{mol dm}^{-3} solution of lactose.
(a) (ii) Describe how the student made a further four solutions of lactose by proportional dilution.
(b) (i) Identify the independent and dependent variables in this investigation.
independent \text{ } .....................
dependent \text{ } .....................
(b) (ii) Suggest a suitable control for this investigation.
(b) (iii) Describe a method that the student could use to find the $K_m$ of lactase at different pH values. The solutions were made as described in (a) (i) and (a) (ii) and the apparatus shown in Fig. 1.2 was used.
Your method should be set out in a logical way and be detailed enough to let another person follow it.
You should not include details of how to make the lactose or lactase solutions.
(c) (i) Complete Fig. 1.3 by sketching a graph to show the effect of substrate concentration at one pH on the initial rate of reaction.
Indicate on your graph how the student could find the $K_m$ value of lactase at that pH.
(c) (ii) Table 1.1 shows the results that the student obtained for $K_m$ at different pH values.
[Table_1]
State which of these pH values, A to E, is closest to the likely optimum pH of lactase.
Explain your answer.
582
536
500
(a) (i) Identify one variable that could be standardised once the young plants are in the test plots in the fields.
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(ii) Suggest one other variable that cannot be standardised once the young plants are in the test plots in the fields.
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(b) Suggest why the researchers used dry mass to estimate the yield of the different crops.
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(c) The data collected by the researchers allowed them to determine, for each crop, the concentration of salt solution at which yield is reduced by 50\%.
Explain how the researchers determined the concentration of salt at which yield is reduced by 50\%.
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(d) State three conclusions that can be made about the effect on the yield of these crops when irrigated with salt solutions.
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(e) Based on these results the agricultural organisations published recommendations to help farmers choose which crops to grow in saline soils.
However, farmers in different parts of the world who followed these recommendations did not obtain the yields expected.
Suggest two reasons for this.
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516
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