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Proceed as follows:
1. Tie a knot in the Visking tubing as close as possible to one end so that it seals the end.
2. To open the other end, wet the Visking tubing and rub the tubing gently between your fingers.
3. Without mixing P, put some of P into the Visking tubing to the level shown in Fig.1.1.
4. Rinse the outside of the Visking tubing by dipping it into the water in the container labelled V.
5. Put the Visking tubing into the large test-tube.
(a) (i) State the volume of W needed to reach the water level as shown in Fig.1.1.
volume of W ....................................... cm$^3$ [1]
(a) (ii) Complete Fig.1.2 to show how you will make four further concentrations of G, starting with the 1\% solution, G. [3]
12. Test each solution separately and record the time taken for the first appearance of any colour change. If there is no colour change after 120 seconds record ‘more than 120’.
(iii) Prepare the space below and record your results. [4]
(iv) Complete Fig. 1.3 below to show
• the positions of each of the percentage concentrations of solution G
• the letter S to show where the sample fits in the series of concentrations. [2]
(v) A colorimeter could not have been used in this investigation.
Describe three other modifications to this investigation which would improve the confidence in your results.
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In a similar investigation, a student investigated how changing the concentration of glucose solution (independent variable) in the Visking tubing affected the quantity of glucose diffusing through the wall into the surrounding solution.
After 20 minutes a dye was added to the surrounding solution. This produced different intensities of colour depending on the glucose concentration in the surrounding solution.
A colorimeter was used to measure the absorbance of light by the coloured solution.
Other variables were considered and kept to a standard.
The student's results are shown in Table 1.1.
Table 1.1
| concentration of glucose solution inside the Visking tubing / arbitrary units | absorbance of light by the coloured solution / arbitrary units |
|---|---|
| 10 | 0.750 |
| 15 | 1.100 |
| 20 | 1.475 |
| 25 | 1.850 |
| 30 | 1.900 |
(b) (i) Plot a graph of the data shown in Table 1.1. [4]
(ii) Explain the difference in the results for the glucose concentration at 10 arbitrary units and at 15 arbitrary units.
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(iii) Explain the difference in the gradients of the line between the glucose concentrations of 10 arbitrary units and 25 arbitrary units and between 25 arbitrary units and 30 arbitrary units.
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(iv) The student used a measuring cylinder to measure the volumes of glucose solution. The smallest division on the measuring cylinder scale was 0.2 cm$^3$.
State the actual error in measuring a volume of 5 cm$^3$ using this measuring cylinder.
5 cm$^3$ ± ....................................... cm$^3$ [1]
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J1 is a slide of a transverse section through a plant root.
(a) (i) Describe one observable feature on J1 which identifies this specimen as a root.
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(ii) Draw a large plan diagram of the whole specimen on J1.
On your diagram, use a label line and label to show the cortex. [4]
(iii) Make a large drawing of one group of four complete touching xylem vessels as observed on the specimen on J1.
On your drawing, use a label line and label to show one lumen.
Annotate your drawing with one observable feature. [5]
Fig. 2.1 shows a diagram of a stage micrometer scale that is being used to calibrate an eyepiece graticule.
One division, on either the stage micrometer scale or the eyepiece graticule, is the distance between two adjacent lines.
The length of one division on this stage micrometer is 0.1 mm.
(b) (i) Using this stage micrometer, where one division is 0.1 mm, calculate the actual length of one eyepiece graticule unit using Fig. 2.1 by completing Fig. 2.2.
Step 1 1 eyepiece graticule unit = divided by = ……………… mm
Step 2 Convert the answer to a measurement with the unit most suitable for use in light microscopy. multiplied by = ……………. [3]
(ii) Fig. 2.3 is a photomicrograph showing part of an organ from a plant of a different species.
Fig. 2.3 shows a photomicrograph taken using the same microscope with the same lenses as Fig. 2.1.
Use the calibration of the eyepiece graticule unit from (b)(i) and Fig. 2.3 to calculate the actual length of the plant tissue from X to Y.
You will lose marks if you do not show all the steps in your calculation and do not use the appropriate units. [2]
(c) Fig. 2.3 is shown again here to help you answer (c).
Prepare the space below so that it is suitable for you to record observable differences between the specimen on slide J1 and in Fig. 2.3, to include:
• the vascular tissue
• at least two other tissues. [5]
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