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(a) (i) Decide the volume of Benedict’s solution you will use for each test.
Complete the table to show the volume of Benedict’s solution you will use.
[Table_1]
solution volume/cm3
Benedict’s
G 4
(ii) Prepare the space below and record your results.
The student’s hypothesis was:
“the time taken for the Benedict’s solution to show the first appearance of a
colour change will decrease as the temperature increases.”
(iii) State whether your results support this hypothesis.
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Use your results to explain your answer.
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(iv) State the temperature you will use.
State a reason for the temperature you have chosen.
temperature ........................................................................
reason ......................................................................................
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(v) Complete Fig. 1.1 to show how you will make two further concentrations of G.
[Image_1: Fig. 1.1 diagram of glucose concentration dilution]
You are now required to carry out a serial dilution of glucose solution, G, to reduce the concentration of G by half between each successive dilution.
You will need 15 cm3 of each glucose concentration.
Fig. 1.1 shows how to make the first concentration of 2% glucose solution.
[Diagram showing dilution steps]
15 cm3 of 4% glucose solution, G
15 cm3 of distilled water, W
30 cm3 of 4% glucose solution, G
30 cm3 of 2% glucose solution, G
(vi) Decide the volumes of solutions you will use in your investigation.
Complete the table.
[Table_2]
solution volume/cm3
Benedict’s
glucose solutions
S1
S2
(viii) Complete Fig. 1.2 below to show:
• each percentage concentration of glucose solution (the concentration of G is shown)
• where the samples S1 and S2 fit in the series of concentrations.
[Image_2: Fig. 1.2 graph of glucose concentration]
0 percentage concentration of glucose G
4
(ix) Describe three modifications to this investigation which would improve the confidence in your results.
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(x) A systematic error occurs when apparatus with scales are used, since the scales may be slightly different.
For example, when measuring the same line, two rulers may give different lengths. However, as long as the same ruler is used for all the measurements, the trend is not affected because the error is consistent.
State one piece of apparatus used in this investigation that may have a systematic error.
Suggest whether this affected your results and give a reason for your answer.
apparatus ..................................................................
reason ......................................................................................
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(a) The eyepiece graticule scale in your microscope may be used to measure the actual length of the layers of tissues or cells, if the scale has been calibrated against a stage micrometer.
However, to help draw the correct shape and proportions of tissues or cells, as in (a)(i) and (a)(ii), it is \textit{not} necessary to calibrate the eyepiece graticule scale.
\textbf{J1} is a stained transverse section through a plant leaf.
This plant species grows in sub-tropical and temperate regions. You are not expected to have studied this leaf.
(i) Draw a large plan diagram of the mid-rib of the leaf on J1. The mid-rib is shown by the shaded area in Fig. 2.1.
On your diagram, use a ruled label line and label to show the xylem.
(ii) Within the vascular bundles the xylem is made up of chains of vessel elements (arranged in lines).
Select \textbf{two} different chains of xylem vessel elements.
Make a large drawing of \textbf{three} complete adjacent (touching) xylem vessel elements from \textbf{each} of these two selected chains.
On your drawing use a ruled label line and label to \textbf{one} lumen.
\textit{first chain}
\textit{second chain}
[4]
(b) Fig. 2.2 is a photomicrograph of the surface of a plant leaf showing stomata. This plant species grows throughout the world’s temperate regions.
(i) Use the magnification on Fig. 2.2 to calculate the actual length, in \mu m, of line X.
You may lose marks if you do not show your working or if you do not use appropriate units.
................................................................. \mu m [4]
(ii) State \textbf{one} observable feature of the leaf surface, shown in Fig. 2.2, that supports the conclusion that water loss was being reduced in this leaf.
Explain how this feature reduces water loss.
\textit{feature} ..........................................................................................................................
\textit{explanation} .........................................................................................................................
[1]
Fig. 2.3 is a photomicrograph of a stained surface of another leaf showing stomata. This plant species is native to North Africa and South-west Asia.
(c) Prepare the space below so that it is suitable for you to record the observable differences between the specimens shown in Fig. 2.2 and in Fig. 2.3. Record your observations in the space you have prepared.
[4]
Rising concentrations of carbon dioxide in the atmosphere have been recorded by scientists for over one hundred years and can be used to predict future increases.
Scientists have studied the effect of carbon dioxide on the number of stomata per mm$^2$ on the upper and lower epidermis of leaves of one species of plant.
A large sample of plants was grown in air containing one of each of the following concentrations of carbon dioxide:
• 380 \mu mol mol$^{-1}$ (the concentration measured in the atmosphere now)
• 560 \mu mol mol$^{-1}$ (the predicted concentration in the atmosphere 50 years in the future)
• 800 \mu mol mol$^{-1}$ (the predicted concentration in the atmosphere 100 years in the future).
All other variables were standardised.
After a set time the number of stomata per mm$^2$ on the upper and lower epidermis of the leaves was found and the mean number of stomata per mm$^2$ was calculated.
The results are shown in Table 2.1.
[Table_1]
(d) \textbf{Plot a chart} of the data shown in Table 2.1.
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