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(a) (i) You will need to select 10 seeds to use in the investigation.
State which variable you will need to standardise (keep the same) when selecting the seeds.
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1. Select your 10 seeds and put them into a large test-tube. Put 3 cm$^3$ of S into the same test-tube and leave for 20 minutes.
2. Set up a water-bath and heat the water to a suitable temperature to test for reducing sugars using the Benedict's test.
(ii) State the temperature you will need to maintain in the water-bath to carry out the Benedict's test.
temperature .................. [1]
(iii) You will need to make dilutions of the 0.4% solution of R, so that the concentration of R is reduced by 0.1% between each successive dilution.
You will need 10 cm$^3$ of each concentration.
Prepare the space below to show the
• concentration of R
• volume of R
• volume of distilled water, W.
(iv) You will need to test the different concentrations of R and 2 cm$^3$ of the solution surrounding the seeds.
State the volume of Benedict's solution and the volume of each of the concentrations of R.
volume of Benedict's solution ..................
volume of each concentration of R .................. [1]
3. Make the dilutions of R you decided in (a) (iii).
4. Using the volumes you decided in (a) (iv) carry out the Benedict's test on your concentrations of R. Record the time taken for the first appearance of a colour change. If there is no colour change after 180 seconds record 'more than 180'.
5. After the seeds have been soaked for 20 minutes, carry out the Benedict's test on the solution surrounding the seeds.
(v) Prepare the space below and record your results.
(vi) Estimate the concentration of reducing sugars in the solution that surrounded the seeds.
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The student's hypothesis was:
"seeds soaked in a sucrose solution release the enzyme, E, which will hydrolyse the sucrose solution into reducing sugars".
(vii) State whether your results support this hypothesis.
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Use your results to explain your answer.
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(b) Describe how you could modify this procedure to investigate the effect of temperature on the release of the enzyme from the seeds.
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(c) (i) Plot a graph of the data shown in Table 1.1. [4]
(ii) Use the data to describe the trend for the activity of the enzyme in the leaves.
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(iii) Explain the change in the activity of the enzyme in the leaves between pH 5.3 and pH 6.4.
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507
583
562
K1 is a slide of a stained transverse section through a plant root. This plant species is a native of Bangladesh, India and Pakistan.
(a) (i) Draw a large plan diagram of the whole specimen on K1.
On your diagram use a label line and label to show the cortex.
[5]
(ii) Make a drawing of one group of five complete cells from the centre of the root.
[4]
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 0.01 mm.
(b) (i) Using this stage micrometer, where one division is 0.01 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 = ext{................} divided by ext{................} = ext{..................} mm
Step 2
Convert the answer to a measurement with the unit most suitable for use in light microscopy.
ext{................} multiplied by ext{................} = ext{................}
[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 total length of the cells labelled X, Y and Z.
You will lose marks if you do not show all the steps in your calculation and do not use the appropriate units.
[2]
Fig. 2.4 is a photomicrograph of a transverse section of an organ from a different plant species.
(c) Prepare the space below so that it is suitable for you to record observable differences between the specimen on slide K1 and in Fig. 2.4. to include:
the vascular tissue
at least two other tissues.
[4]
508
526
510
