A-LevelBiologyCell structure9700/33 · Feb/Mar 2019 · Q219 Marks

P1 is a slide of a stained transverse section through a plant stem. You are not expected to be familiar with this specimen.

(a)(i)Draw a large plan diagram of the area you have selected on P1, to include: • part of the epidermis • only two vascular bundles • any other observable tissues. You are expected to draw the correct shapes and proportions of the different tissues. Use one ruled label line and label to identify the cortex.[5]
(a)(ii)Observe the vascular bundles in the stem on P1. Select one large xylem vessel element and three cells that touch this xylem vessel element. Make a large drawing of this group of four cells. Each cell must touch at least two of the other cells. Use one ruled label line and label to identify the lumen in one of the cells.[6]
(b)(i)In Fig. 2.1, the lines R, S and T are drawn across the length of three vascular bundles. Measure the length in the photomicrograph of these three vascular bundles, along the lines R, S and T. length of R length of S length of T[2]
(b)(ii)Using the lengths measured in (b)(i), calculate the mean length in the photomicrograph of these three vascular bundles. Show all the steps in your working. working: mean length[2]
(b)(iii)The magnification of the photomicrograph in Fig. 2.1 is x66. Use your answer to (b)(ii) and the magnification of the photomicrograph in Fig. 2.1 to calculate the mean actual length of these three vascular bundles, in μm. Show all the steps in your working. working: mean actual length[2]
(b)(iv)You are required to annotate Fig. 2.2 to describe two observable differences between the stem in Fig. 2.2 and the stem in P1. Ignore any differences in colour and size. • Draw lines to label two features of the stem in Fig. 2.2 that are different from the corresponding features of the stem in P1. • Label one line J and the other line K. • Next to each letter, describe how the labelled feature is different from the corresponding feature of the stem in P1.[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 2019). The mark or mark type is shown in brackets.

[5] minimum size and draws at least 2 layers of tissue and no cells; draws epidermis and only 2 vascular bundles; draws at least one tissue layer passing through vascular bundles; subdivides vascular bundles; label line and label to identify the cortex;
[6] minimum cell size and lines thin and continuous; draws only four cells; draws one large xylem vessel and 3 cells touching the xylem vessel and each cell touching at least 2 of the other cells; two lines drawn around each cell and three lines where cells touch; the size of largest cell is at least three times the size of the smallest cell; label line and label to identify the lumen of one of the cells ;
[2] correctly measures lengths of vascular bundles, R, S and T; uses the same units for lengths R, S and T;
[2] shows 3 lengths added together and divided by 3; correct mean length ;
[2] shows answer from (b)(ii) multiplied by 1000 (for mm) or 10000 (for cm) and divided by 66 ; correct answer ;
[2] line labelled J drawn to observable feature (e.g. epidermis of Fig. 2.2); and description of difference (e.g. in P1 the epidermis is continuous); line labelled K drawn to observable feature (e.g. vascular bundle of Fig. 2.2); and description of difference (e.g. in P1 the vascular tissue is in a ring near to the epidermis);