No questions found
(a) State the hazard with the greatest level of risk when using the apparatus and reagents in step 1 on page 4.
State the level of risk of the procedure: low or medium or high.
hazard ............................................................................................................................
level of risk ..................................................................................................................
(b) (i) You are required to make a serial dilution of the 5% urea solution, U, which reduces the concentration of the urea solution by half between each successive dilution.
You will need to prepare 40 \text{cm}^{3} of each concentration.
You should use the beakers shown in Fig. 1.1 to show how you will prepare the serial dilutions.
For each beaker, complete Fig. 1.1 to show how you will dilute the solution by:
• stating, under the beaker, the concentration and volume of the urea solution available for use in the investigation
• using one arrow, with a label above the beaker, to show the concentration and volume of urea solution added to prepare the concentration
• using another arrow, with a label above the beaker, to show the volume of W added to prepare the concentration.
[Image_1 - Fig. 1.1]
(b) (ii) Prepare the space below and record your results.
(iii) Significant sources of error may cause some of the raw data to be inaccurate, producing anomalous results.
• The end-point of this investigation was the change in colour of the red litmus paper. State how this might have caused the results to be inaccurate.
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• Identify one other significant source of error for this investigation.
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(iv) Describe one improvement to this investigation which would increase confidence in your results.
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(v) State one piece of apparatus used in this investigation that may have a systematic error.
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(vi) When a student carried out this investigation, the red litmus paper changed to blue in a very short time. This made measuring the time inaccurate.
Describe how the student could change the procedure to increase the time taken to reach the end-point.
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(c) The ‘urea breath test’ is used to detect human stomach infections caused by bacteria. If the bacteria are present in the stomach, an enzyme produced by the bacteria breaks down the urea to carbon dioxide. This carbon dioxide is absorbed from the stomach into the blood and travels to the lungs where it is released in the breath.
To test for the presence of the bacteria, the patient drinks a solution of urea containing $^{13}$C, which is an isotope of carbon. The breath of the patient is then sampled at intervals for 110 minutes and analysed for the presence of $^{13}$CO$_{2}$ (carbon dioxide containing $^{13}$C).
The results are shown in Table 1.1.
[Table_1]
You are required to use a sharp pencil for graphs.
(i) Plot a graph of the data in Table 1.1.
[4]
(ii) Using your knowledge of enzymes, explain the trend shown in the data.
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522
(a) K1 is a slide of a stained transverse section through a plant stem. This plant genus grows in Europe, Africa and Asia. You are not expected to be familiar with this specimen.
(i) Draw a large plan diagram of the half of the stem, as shown in Fig. 2.1.
Use one ruled label line and label to identify the pith.
[5]
(ii) Observe a corner or bulge of the stem.
Select and make a large drawing of:
• two whole, adjacent cells from the epidermis which touch each other
• two whole, adjacent cells from the cortex (the layer of tissue under the epidermis) which touch each other.
The drawings should show any difference in size (linear magnification) observed between each pair of cells.
Use one ruled label line and label to identify one cell wall.
cells from epidermis
cells from cortex
[5]
(b) Fig. 2.2 is a stained transverse section through the stem of a different plant species. This plant species grows throughout the world.
You are not expected to be familiar with this specimen.
A student calibrated the eyepiece graticule in a light microscope using a stage micrometer scale so that the actual length of specimens could be found.
The calibration was: one eyepiece graticule division equal to 0.028 mm.
(i) The use of the unit mm is not the most appropriate unit for use with the light microscope.
State which unit is the most appropriate for use with the light microscope and show how the value 0.028 mm is converted to this unit.
You may lose marks if you do not show your working.
[2]
(ii) Fig. 2.2 shows a photomicrograph taken using the same microscope with the same lenses as the student.
Use the calibration of the eyepiece graticule division from (b)(i) and line X in Fig. 2.2 to calculate the actual total width of the tissue as shown by line X.
You may lose marks if you do not show all your working and do not use the appropriate units.
actual width of the tissue shown by line X ..........................................................
[2]
(iii) Suggest one observable feature of the stem in Fig. 2.2 which supports the conclusion that this is from a plant growing in a freshwater pond.
Explain how this feature supports this conclusion.
feature .............................................................................................................................
explanation .................................................................................................................. ................................................................................................................................................
[1]
(c) Prepare the space below so that it is suitable for you to record observable differences between the specimen on K1 and Fig. 2.2.
Record your observations in the space you have prepared.
[4]
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531
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