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(a) You need to decide which objective lens you will use and decide the number of cells you will need to observe to give you confidence in your results.
(i) State the objective lens you will use and the number of cells you will observe. Explain how this will give you confidence in your results.
objective lens .................................................. number of cells .................................................
explanation ............................................................................................................................................
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(a) (i) Record your results in an appropriate table.
(b) Observe the onion cells on the microscope slide you labelled S4.
Select four adjacent, touching cells, with at least two cells showing plasmolysis.
Make a large drawing of these four cells.
Use one ruled label line and label to identify the cell surface membrane of one cell.
(c) A student investigated the effect of different concentrations of sucrose solutions on pieces of potato tissue.
• Each piece of potato tissue was cut to exactly 50 mm in length and had a cross-sectional area of exactly 10 mm × 10 mm.
• Each piece of potato tissue was put into a different concentration of sucrose solution.
• After 1 hour the length of each piece of potato was measured.
The results of the student's investigation are shown in Table 1.2.
[Table]
(i) Describe the pattern of water movement shown in Table 1.2.
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(ii) Using your knowledge of water potential, explain the result at 0.2 mol dm⁻³.
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(iii) The student decided to compare the effect of different concentrations of sucrose solution using a different type of potato.
Complete Table 1.3 to suggest how three variables would need to be standardised.
[Table]
539
553
558
(a) A student investigated the effect of different factors on transpiration.
In the investigation, three identical plants were put in flasks containing 70 $cm^3$ of water as shown in Fig. 2.1.
Fig. 2.1
The plants were each kept in different conditions:
• 20 °C + still air + high humidity
• 20 °C + windy + low humidity
• 30 °C + still air + low humidity.
All other variables were kept constant.
After 4 hours the water remaining in each flask was put into beakers labelled \textbf{P1, P2 and P3}.
(i) Suggest a suitable control for this investigation.
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(ii) Describe how the student could have decreased the humidity.
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You have been given the beakers, labelled \textbf{P1, P2 and P3}, containing the water that was collected from each flask after the 4 hours.
You will need to determine the volume of water \textbf{lost} by transpiration from each plant.
(iii) Using the apparatus provided, measure the volume of water in \textbf{P1, P2 and P3}.
Calculate the volume of water lost through transpiration by \textbf{each} plant.
Record your results in an appropriate table. [2]
(iv) State which plant was grown in high humidity.
Give a reason for your answer.
\textit{plant} ..........................................................................................................................
\textit{reason} .........................................................................................................................
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(b) Plants lose water through stomata by transpiration.
A scientist investigated the effect of carbon dioxide concentration in the air on the number of stomata present per $mm^2$ of leaf area, in five plants. The carbon dioxide concentration was measured in parts per million (ppm).
\textbf{Table 2.1}
[Table_1]
(i) Complete Table 2.1 by calculating the mean number of stomata/$mm^2$ at a carbon dioxide concentration of 357 ppm.
Show all the steps in your working and use appropriate units. [2]
(ii) Plot a graph of the mean results shown in Table 2.1 on the grid in Fig. 2.2.
The first values for the \textit{x}-axis and the \textit{y}-axis are shown on the grid in Fig. 2.2.
\textit{Use a sharp pencil for drawing graphs.} [4]
Fig. 2.2
(iii) Describe the trend shown by your graph in Fig. 2.2.
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(iv) A plant has 302 stomata/$mm^2$.
Use your graph in Fig. 2.2 to determine the carbon dioxide concentration in the air where this plant is growing.
carbon dioxide concentration = ........................................................... ppm [1]
(c) Fig. 2.3 is a photomicrograph of a stained transverse section through a leaf.
You are not expected to be familiar with this specimen.
Fig. 2.3
\textit{Use a sharp pencil for drawings.}
You are expected to draw the correct shape and proportions of the different tissues.
Draw a large plan diagram of the \textbf{whole} leaf shown in Fig. 2.3.
Use \textbf{one} ruled label line and label to identify the epidermis. [5]
(d) Fig. 2.4 shows the same photomicrograph as in Fig. 2.3, with an eyepiece graticule scale added.
The calibration of the eyepiece graticule scale is:
1 eyepiece graticule division = 39.7 μm.
Fig. 2.4
Use the calibration of the eyepiece graticule scale and Fig. 2.4 to calculate the actual width of the vascular bundle, shown by line \textbf{X - Y}.
Show all the steps in your working and use appropriate units.
actual width of the vascular bundle = ...........................................................
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519
538
519
