A-LevelBiologyTransport in plants9700/32 · May/June 2017 · Q218 Marks

M1 is a slide of a stained transverse section through a plant stem. You are not expected to be familiar with this specimen.

(a)Observe the different tissues on M1 and select a field of view that shows part of the epidermis and the vascular bundles. Use a sharp pencil for drawing.
(a)(i)Draw a large plan diagram from the selected field of view which shows: • part of the epidermis • only three vascular bundles • any other observable tissues. You are expected to draw the correct shape and proportions of the different tissues. Use one ruled label line and label to identify the xylem in one vascular bundle.[5]
(a)(ii)Observe the central tissue in the stem on M1. These cells are not identical. Select one group of four adjacent (touching) cells which show some of the differences between these cells. Each cell must touch at least 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 cell wall of one cell.[5]
(b)Fig. 2.1 is a photomicrograph of a stained transverse section through a stem of a different type of plant. You are not expected to be familiar with this specimen. [Figure 2.1]
(b)(i)Prepare the space below so that it is suitable for you to record the observable differences between the stem on M1 and the stem in Fig. 2.1. Record your observations in the space you have prepared.[4]
(b)(ii)You are required to find the area of the xylem tissue and the area of the vascular bundle. • Draw on Fig. 2.2 an outline around the xylem tissue. • Draw on Fig. 2.2 an outline around the vascular bundle. • Count the number of 1 cm x 1 cm squares within each outline. Count any 'half square' or 'more than half square' as one square. Do not count any square that is 'less than half a square'. • Show on your grid all of the 1 cm × 1 cm squares that you have counted. State the area of the xylem tissue and the area of the vascular bundle. area of xylem tissue .............................................................. area of vascular bundle ..............................................................[2]
(b)(iii)Calculate the area of the xylem tissue as a percentage of the area of the vascular bundle. You may lose marks if you do not show your working. answer = .............................................. %[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

[5] minimum size at least 90 mm + at least 3 vascular bundles drawn ;
[5] no cells + at least one enclosed area beneath epidermis with each end of enclosed area touching epidermis + only 3 vascular bundles drawn ;
[5] decides to subdivide vascular bundle into at least two areas;
[5] epidermis drawn as two lines ;
[5] uses one label line + one label to xylem ;
[5] quality of line for outer wall of cells (thin line) + minimum size at least 40mm across largest cell + no shading;
[5] only four cells drawn, each cell touching at least two other cells ;
[5] cell walls drawn as two lines close together ;
[5] at least one cell drawn with at least five sides;
[5] uses one label line + one label to cell wall ;
[4] organises comparison into three columns with one column for features, one column headed M1 and one column headed Fig. 2.1 ;
[4] any three observable differences of comparison ;;;
[2] shows squares counted on Fig. 2.2 ;
[2] uses correct units (cm²) for area of xylem tissue and area of vascular bundle ;
[2] shows value for area of xylem tissue divided by value for area of vascular bundle × 100 ;
[2] shows answer to appropriate degree of accuracy;