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Many plants produce two types of leaves. One type is produced where the leaves develop in full sunlight and are called ‘sun leaves’. The other type is produced where the leaves develop in the shade and are called ‘shade leaves’.
A student investigated photosynthesis in both types of leaves using leaf discs. Fig. 1.1 shows the method used by the student to obtain the leaf discs.
The student then carried out the following actions:
3. replaced the plunger into the syringe, turned the syringe upside down and pushed in the plunger to force out all the air
4. placed a finger over the open end of the syringe and pulled down the plunger to create a vacuum
5. tapped the side of the syringe to remove air bubbles
6. repeated actions 3–5 until the leaf discs sank to the bottom of the syringe.
The student measured the rate of photosynthesis of discs from both types of leaves to test the hypothesis
Leaf discs from shade leaves will photosynthesise at a higher rate in low light intensity than leaf discs from sun leaves.
Fig. 1.2 shows the appearance of the leaf discs in the syringe as they photosynthesise.
(a) (i) Explain why the leaf discs rise to the surface in the light.
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(ii) Using this method, outline how the student could test the hypothesis.
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Fig. 1.3 shows the results that the student plotted from the investigation.
(b) (i) Suggest labels for the axes of this graph.
x-axis ..................................................................................................
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y-axis .................................................................................................
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(ii) State two ways in which the student’s data support the hypothesis.
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In a further investigation using these two types of leaves, the student estimated the number of stomata per unit area. Epidermal strips from the lower surface of the leaf were mounted in water and observed under a microscope.
The diameter of the field of view was measured using an eyepiece graticule. The actual field of view was calculated using a calibration value from a slide micrometer scale.
Diameter of field of view at \times 100 magnification = 0.5mm
(c) (i) Calculate the area of the field of view. Use the formula $\pi r^2$. $(\pi = \frac{22}{7}$ or $\pi = 3.14)$
Give your answer to one significant figure.
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(ii) Table 1.1 shows the results of the stomatal count investigation.
[Table_1]
Calculate the mean number of stomata per mm2 for the shade leaves.
Show your working below and write your answer in Table 1.1.
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(iii) State the null hypothesis for a statistical test to find out whether the difference in the number of stomata is significant.
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(iv) Name a statistical test that could be used and give the reason for your answer.
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(d) The results of the statistical test showed that the difference was significant. Suggest one reason why there is a difference in the number of stomata of shade leaves and sun leaves.
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558
501
554
(a) (i) Suggest one variable that must be controlled in this procedure.
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(ii) State the independent variable in this investigation.
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(iii) Both test organisms had antibodies against antigen X, but only organism 2 had antibodies against antigen Y.
On Fig. 2.2 draw lines to represent where precipitation might have occurred for both organisms. [2]
(b) Suggest two disadvantages of immunodiffusion for detecting antigens.
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(c) A naturally occurring mutant of Plasmodium sp. has been tested for use as a 'whole organism' vaccination against malaria. The mutant organism develops normally in mosquito vectors and infects the salivary glands in the same way as non-mutant wild type Plasmodium sp. In mice, the mutant infects liver cells but does not multiply and cannot enter red blood cells.
Trials using mice were carried out and the effectiveness of the mutant organism as a vaccine tested by injecting non-mutant wild type Plasmodium sp. into vaccinated and non-vaccinated mice.
Table 2.1 shows the results of investigations in mice using the mutant Plasmodium sp.
[Table_1]
(i) Suggest the purpose of including each of the following test groups.
group 1 ..............................................................................................................................
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groups 2 and 3 ..............................................................................................................................
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group 4 ..............................................................................................................................
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(ii) Using the information in the question, outline a procedure that might be used to obtain mutant Plasmodium sp. to use in the vaccination trials.
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564
526
588
