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(a) (i) Complete Fig. 1.1 to show how you will make three further concentrations of substrate solution, S. [3]
Proceed as follows:
1. Prepare the concentrations of substrate solution as shown in Fig. 1.1, in the containers provided.
2. Put 2 cm3 of 0.1% substrate solution, S into a labelled test-tube.
3. Put 0.5 cm3 of phenolphthalein solution into the same test-tube.
4. Put 1 cm3 of enzyme E into the same test-tube. Mix and start timing.
5. Record the time taken to reach the end-point of the reaction.
If the end-point is not reached at ten minutes, record 'more than 600' for that concentration.
6. Repeat steps 2 to 5 with each of the concentrations of substrate solution.
(ii) Prepare the space below and record your observations. [5]
(iii) State one variable which should have been controlled and how you could modify this procedure so that this variable would be controlled. [1]
(iv) Describe two ways in which the accuracy of the results could be improved. [2]
[Image: Fig. 1.1 shows how to make the first concentration of 0.05% substrate solution.]
(b) (i) Plot a graph of the data shown in Table 1.1 [4]
The student’s results are shown in Table 1.1.
[Table: Table 1.1]
(ii) Estimate the concentration of inhibitor which would produce an inhibition area of 100 mm2. Show on your graph where you obtained the estimate.
concentration .......... μg cm-3 [1]
(iii) Describe the trend shown in your graph. [2]
(iv) Explain the effect of changing the concentration of the inhibitor. [2]
[Image: Fig. 1.2 shows a diagram of the strip of agar gel after adding the dye.]
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J1 is a slide of a stained transverse section through a plant stem. The genus of this plant is found in Europe, Asia, Africa and Australia.
[Image_1: Fig. 2.1]
(a) (i) Draw a large plan diagram of the part of the stem indicated by the shaded area in Fig. 2.1. Label the epidermis.
In this stem, crossing the air space, are chains of cells which are attached to the tissue surrounding the vascular bundle. Select a chain of cells which is attached by only one cell to the tissues surrounding the vascular bundle. The cells should have distinct cell walls and cell contents.
(ii) Make a large drawing of
• two adjacent (touching) chain cells and
• one cell that attaches these two cells to the tissue surrounding the vascular bundle.
There should be only one group of three cells in your drawing. Label a cell wall.
(iii) Suggest one observable feature of J1 which supports the conclusion that this is a stem from a plant living in water. Suggest how this feature may help the plant to live in water.
Fig. 2.2 is a photomicrograph of a transverse section of a stem from a different plant species. The genus of this plant is found in Europe, North Africa and the Middle East. To find the mean length of an air space, a student measured five air spaces, as shown in Fig. 2.2.
[Image_2: Fig. 2.2]
(b) (i) Use the magnification to calculate the mean actual length, in µm, of an air space using R, V, X, Y and Z. You may lose marks if you do not show your working or if you do not use appropriate units.
(ii) Prepare the space below so that it is suitable for you to record one observable similarity and two observable differences between the specimen on J1 and in Fig. 2.2. Record your observations in the space you have prepared.
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