AS & A Level Biology - 9700 Paper 3 2015 Winter Zone 1

(a) You are required to make a serial dilution of the 10% sodium chloride solution, S, which reduces the concentration of the sodium chloride solution by a factor of ten between each successive dilution. You will need to prepare 20 cm³ of each concentration. (i) Complete Fig. 1.1 to show how you will dilute the solution. You should use the two beakers shown in Fig. 1.1 and draw as many extra beakers as you need to prepare sufficient concentrations for the investigation. For each beaker: • state, under the beaker, the volume and concentration of the sodium chloride solution available for use in the investigation • use one arrow, with a label above the beaker, to show the volume and concentration of sodium chloride solution added to prepare the concentration • use another arrow, with a label above the beaker, to show the volume of W added to prepare the concentration. [Image with Beakers]

(a)(ii) The volume of solution surrounding the plant tissue in the test-tube is a variable that must be standardised. One piece of plant tissue will be put into each test-tube with sodium chloride solution. State the volume of solution that you will use in each test-tube. Explain why you have selected this volume. volume ................................................ reason for selecting this volume ...............................................................

(a)(iii) After 10 minutes you will need to remove the plant tissue from each test-tube so that the colour of each solution can be recorded. Record your observations in (a)(iii).

(a)(iv) State the hazard with the greatest level of risk when carrying out steps 2 to 8 on page 4. State the level of risk of the procedure: low or medium or high. hazard ........................................ level of risk ........................................

(a)(v) The test-tube containing water and stained potato is a control experiment for this investigation. Explain why it is necessary to collect this result.

(a)(vi) With reference to the experiment you have just carried out, explain why the use of a 1 cm³ syringe that can measure to an accuracy of 0.01 cm³ would not increase the accuracy of your results.

(b) A scientist investigated the effect of concentration of sodium chloride solution on the increase in length of the roots of a fruit tree. Nutrient solutions were prepared containing two different concentrations of sodium chloride solution, 1 mM and 25 mM. 10 young fruit trees were placed so that their roots were in 1 mM sodium chloride solution and another 10 young fruit trees were placed so that their roots were in 25 mM sodium chloride solution. The root length of each of the trees was measured and the mean length of roots recorded at intervals over a period of 10 days. The results are shown in Table 1.1. [Table 1.1]

(b)(i) Plot a graph of the data shown in Table 1.1. [4 marks]

(b)(ii) Using the data in Table 1.1, the rate at which root length increased between day 3 and day 5 for trees in 1 mM is calculated as 2.00 mm day^-1. Use the data in Table 1.1 to calculate the rate at which root length increased between day 3 and day 5 for plants in 25 mM sodium chloride solution. You may lose marks if you do not show your working. answer .................................... mm day^-1

(b)(iii) The increase in length of the roots occurs due to an increase in cell numbers following mitosis. These cells then become longer as they take up water by osmosis. Explain the difference in the rates between day 3 and day 5 for the two concentrations of sodium chloride solution.

(b)(iv) This scientist investigated the effect of concentration of sodium chloride solution on the increase in length of the roots of a fruit tree. Consider how you would modify this investigation to find the effect of temperature on the increase in length of the roots of a fruit tree in 1 mM sodium chloride solution. Describe how the independent variable (temperature) will be investigated. Describe how one other variable will be standardised.

(a) (i) Draw a large plan diagram of the part of the leaf indicated by the shaded area in Fig. 2.1.
[Image: Fig. 2.1]
On your diagram use one ruled label line and label to identify one feature that adapts the plant to living in a dry habitat.
Annotate this label to explain how the feature you have identified adapts this plant to living in a dry habitat.
(ii) Select one group of four cells from the tissue below the vascular bundle found in the centre of the leaf. Each cell in the group should touch two of the other cells.
Make a large drawing of this group of four cells.
Use one ruled label line and label to identify the cytoplasm of one cell.

(b) Fig. 2.2 is a photomicrograph of a stained transverse section through a leaf of a different xerophytic plant species.
[Image: Fig. 2.2]
(i) On Fig. 2.2, use a label line and the label 'X' to suggest the position of the xylem tissue in the leaf. [1]
(ii) A student calibrated the eyepiece graticule in a light microscope using a stage micrometer scale so that the actual width of the leaf could be found.
The calibration was: one eyepiece graticule division equal to 0.012 mm.
This is converted to one eyepiece graticule division equal to 12 μm, which is the most appropriate units for use with the light microscope.
Fig. 2.2 shows a photomicrograph taken using the same microscope with the same lenses as those used by the student.
Use the calibration of the eyepiece graticule division and Fig. 2.2 to calculate the actual width of the leaf, as shown by line Y.
You may lose marks if you do not show your working. .............................. μm [3]

(c) The leaf on slide J1 and the leaf in Fig. 2.2 are adapted to living in dry conditions.
Prepare the space below so that it is suitable for you to record observable differences in xerophytic adaptations between these two specimens.
Record your observations in the space you have prepared.