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Fig. 1.1 shows one type of potometer used by a student to investigate transpiration.
(a) (i) Suggest a hypothesis the student could test about the transpiration of a mesophyte (a plant adapted to a moist environment) and a xerophyte (a plant adapted to a dry environment).
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(ii) Using this potometer, outline a procedure that the student could use to test this hypothesis.
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(iii) The capillary tube measures the distance moved by the water. Explain how the actual volume of water lost can be calculated.
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(b) Sketch a graph to predict the expected results of the investigation.
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(c) (i) The student then measured the surface area of the leaves by tracing the outline on a grid and counting the number of squares covered by the leaves. This area was doubled.
Mesophyte:
surface area of leaves = 36 cm^2
water loss in 30 minutes = 0.018 cm^3
Calculate the rate of water loss in cm^3 m^{-2} min^{-1}.
Show all the steps in your calculation.
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(ii) State a statistical test that the student could use to find out if the difference in water loss between the two types of leaf is significant. State a reason for your choice.
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(d) In a further investigation the student measured the loss in mass of each type of leaf.
Fig. 1.2 shows the experimental set-up.
Table 1.1 shows the results of this investigation.
[Table_1]
State three conclusions that can be drawn from these results.
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516
563
517
The effects of the concentration of two amino acids was tested on the growth of fibroblast cells from mice. The following procedure was used:
- a culture of 2000–3000 cells was added to a growth medium containing all the required nutrients other than the amino acids being tested
- a total of ten cultures were used for each concentration of amino acid
- the cells in the culture were fed every two days with fresh amino acid solution
- after 6 days five cell samples from each of the cultures were counted
- the proportional increase in cell number was calculated for each culture.
Table 2.1 shows the results of this investigation.
[Table_1]
(a) State two variables that should be controlled in this investigation. For each, suggest a method by which it might be controlled.
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(b) Explain how the proportional increase in cell number is calculated.
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(c) The hypothesis tested was Growth of fibroblasts is stimulated by glutamine and inhibited by glutamic acid.
Assess how far the results support the hypothesis.
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532
512
577
