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(a) (i) Complete Fig. 1.2 to show how you will make three further concentrations of calcium chloride solution by serial dilution.
Proceed as follows:
1. Prepare all the concentrations of calcium chloride solution as shown in Fig. 1.2 in the containers provided.
2. You are provided with a water-bath. Adjust the temperature to between 35\(^{\circ}\)C and 40\(^{\circ}\)C. You will need to maintain this temperature during steps 3 to 10.
3. Put 1 cm\(^3\) of each of the four concentrations of calcium chloride solution into separate test-tubes.
4. Put 10 cm\(^3\) of M into each test-tube.
5. Gently shake each of the test-tubes to mix M and calcium chloride solution.
6. Put the test-tubes into the water-bath and leave for at least three minutes.
Read steps 7 to 11 before proceeding.
7. Remove the test-tube containing the mixture with the highest concentration of the calcium chloride solution from the water-bath. The process of coagulation will start when E is added to each test-tube.
Put 1 cm\(^3\) of solution E, so that it runs down the side of the test-tube to form a layer on the surface of the mixture as shown in Fig. 1.3.
8. Gently shake the test-tube to mix the solutions and start timing.
9. Gently rotate the test-tube, as shown in Fig. 1.1 on page 2, to form a film of milk on the inside of the test-tube.
10. Continue to rotate the test-tube whilst holding it over the black card on the table (see Fig. 1.4).
Record the time to reach the end-point as shown in stage 3 in Fig. 1.1. Ignore any small bubbles on the inside of the test-tube. If the end-point has not been reached by 4 minutes, stop the experiment and record 'more than 240'.
11. Repeat steps 7 to 10 using the other concentrations of calcium chloride solution.
(ii) Prepare the space below and record your results.
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[5]
(iii) Identify one significant source of error in measuring the dependent variable in this investigation.
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[1]
(iv) 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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(v) Describe a suitable control for this investigation.
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(b) (i) State two variables that need to be kept the same (standardised) in this investigation. Describe how you would standardise each of these variables.
variable 1 ..............................................................................................................................
description ..............................................................................................................................
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variable 2 ..............................................................................................................................
description ..............................................................................................................................
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[2]
The results of this investigation are shown in Table 1.1.
Table 1.1
[Table_1]
(ii) Plot a graph of the data shown in Table 1.1.
[Graph_1]
[4]
(iii) Explain the trend shown in your graph.
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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 proportion of tissues, as in (a), it is not necessary to calibrate the eyepiece graticule scale.
L1 is a stained, longitudinal section showing the tissues of a young root tip.
(a) Draw a large plan diagram of L1.
Use a ruled label line and a label to show the position of the area in which you can see cells showing stages of mitosis.
Fig. 2.1 is a photomicrograph of root cells.
[Image_1: Fig. 2.1]
(b) Make a large drawing of each of the five cells labelled P, Q, R, S and T on Fig. 2.1.
On your drawing use ruled label lines and labels to identify two different stages of mitosis.
Annotate one of the stages to describe one observable feature that supports your identification.
(c) Use the scale bar below Fig. 2.2 to calculate the magnification of Fig. 2.2.
You may lose marks if you do not show your working or if you do not use appropriate units.
[Image_2: Fig. 2.2]
(d) Prepare the space below so that it is suitable for you to record the observable differences, other than colour, between the specimens in Fig. 2.1 and in Fig. 2.2.
Record your observations in the space you have prepared.
[Image_1: Fig. 2.1]
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