A-LevelBiologyCell structure9700/33 · Feb/Mar 2022 · Q217 Marks

J1 is a slide of a stained transverse section through a plant stem.

(a)(i)Draw a large plan diagram of the region of the stem on slide J1 indicated by the shaded area in Fig. 2.1. Use a sharp pencil. [Figure 2.1] Use one ruled label line and label to identify the xylem.[5]
(a)(ii)Observe one vascular bundle in the stem on slide J1. Select four adjacent touching xylem vessel elements that are arranged in a line. Each of these four xylem vessel elements must touch at least one other. • Make a large drawing of the line of four xylem vessel elements that you have selected. • Use one ruled label line and label to identify one lumen.[5]
(b)Fig. 2.2 is a photomicrograph of a transverse section through a stem of a different type of plant. [Figure 2.2] Identify three observable differences, other than size and colour, between the stem on slide J1 and the stem in Fig. 2.2. Record these three observable differences in Table 2.1. [Table 2.1][3]
(c)(i)Fig. 2.3 is the same photomicrograph as the transverse section of the stem shown in Fig. 2.2. [Figure 2.3] Measure the lengths of the lines L1, L2, L3, L4 and L5 in Fig. 2.3. The lines have been drawn along the lengths of five air spaces. Calculate the mean length of the five lines. Show your working. length of L1 = length of L2 = length of L3 = length of L4 = length of L5 = mean length of lines = [2]
(c)(ii)Using the magnification stated in Fig. 2.3, calculate the actual mean length of the air spaces labelled L1, L2, L3, L4 and L5. Show your working. actual mean length = [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 (Feb/Mar 2022). The mark or mark type is shown in brackets.

[1] uses most of the available space and shows three or more tissue layers ;
[1] draws only the region indicated (quarter of stem) and no cells;
[1] draws epidermis as two lines;
[1] correct proportions of vascular bundle and tissue above ;
[1] label line and label to xylem ;
[1] uses most of the available space and lines continuous, thin and sharp ;
[1] draws only four whole vessels and each vessel touches at least one other and in a line;
[1] two lines around each vessel and three lines where vessels touch ;
[1] correct shape of vessels ;
[1] label line and label to one lumen ;
[1] feature: number of vascular bundles, slide J1: many, Fig. 2.2: few ;
[1] feature: position of vascular bundles, slide J1: peripheral, Fig. 2.2: central ;
[1] feature: vascular bundles, slide J1: joined, Fig. 2.2: separate ;
[1] feature: air spaces, slide J1: absent, Fig. 2.2: present ;
[1] feature: sclereids / AW, slide J1: absent, Fig. 2.2: present ;
[1] AVP described described ;
[1] records correct length of five air spaces and units ;
[1] shows addition of five measurements and division by five ;
[1] shows division by magnification (×48) ;
[1] correct numerical answer matched with appropriate units ;

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