A-LevelBiologyCell structure9700/33 · Feb/Mar 2021 · Q219 Marks

P1 is a slide of a stained transverse section through a plant stem.

(a)(i)(a) Set up the microscope so that you can observe different tissues in the area of the stem on P1 shown by the shaded region in [Figure 2.1]. Use a sharp pencil for drawings. (i) Draw a large plan diagram of the area of the stem on P1 shown by the shaded region in [Figure 2.1]. Your drawing should show the correct shapes and proportions of the different tissues. Use one ruled label line and label to identify the epidermis.[5]
(a)(ii)(ii) Observe the cells in the central tissue of the stem on P1. Select four adjacent, touching cells of the central tissue. Each cell that you select must touch at least two of the other cells. • Make a large drawing of this group of four touching cells. • Use one ruled label line and label to identify the cell wall of one cell.[5]
(b)(i)(b) [Figure 2.2] is a photomicrograph of a stained transverse section through a stem of a different type of plant. This plant is adapted to live submerged in water. (i) Calculate the total area, in mm², of the image of the stem shown in [Figure 2.2]. • Assume that the stem is circular in cross-section. • Measure the diameter of the image of the stem along line M–M. • Show your working. The formula for calculating the area of a circle is: area = 3.14 x r² (r = radius) area = .......................................................................................... mm²[3]
(b)(ii)(ii) In [Figure 2.2], the tissue that contains air spaces has an area in the image of 4500 mm². Use your answer to (b)(i) to calculate the percentage area of the stem shown in [Figure 2.2] that contains air spaces. percentage area = .......................................................................[1]
(b)(iii)(iii) The presence of a large number of air spaces in the stem is one adaptation of the plant shown in [Figure 2.2] for living submerged in water. Suggest a function of these air spaces.[1]
(c)(c) [Figure 2.3] is a photomicrograph of the same stem section that is shown in [Figure 2.2]. One difference between the stem shown in [Figure 2.3] and the stem on slide P1 is the presence of air spaces in the stem shown in [Figure 2.3]. Identify other observable differences between the stem shown in [Figure 2.3] and the stem on slide P1. Record these observable differences in an appropriate table.[4]

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 2021). The mark or mark type is shown in brackets.

[1] (a)(i) appropriate size to fill most of space available and draws at least two layers of tissue ;
[1] (a)(i) draws quarter of the stem and no cells ;
[1] (a)(i) draws tissues to correct proportions ;
[1] (a)(i) draws correct shape of stem and shows layers of different tissues;
[1] (a)(i) label line and label to identify the epidermis ;
[1] (a)(ii) appropriate size of cells to fill most of space available and lines thin and continuous ;
[1] (a)(ii) draws only four cells and each cell touching at least two of the other cells ;
[1] (a)(ii) two lines drawn around each cell and three lines where cells touch;
[1] (a)(ii) correct shape of cells;
[1] (a)(ii) label line and label to identify the cell wall of one of the cells ;
[1] (b)(i) correct diameter of the stem and units ;
[1] (b)(i) value for the radius squared and multiplied by 3.14 ;
[1] (b)(i) correct answer ;
[1] (b)(ii) answer to appropriate number of decimal places;
[1] (b)(iii) buoyancy / transport of oxygen / transport of carbon dioxide;
[1] (c) draws table with headings for P1 and Fig. 2.3 and column for features / compared features in same row ;
[1] (c) e.g. vascular tissue close to the epidermis in P1 and in the centre in Fig. 2.3
[1] (c) e.g. centre of stem in P1 filled with large cells and in Fig. 2.3 filled with small cells
[1] (c) e.g. outside of stem in P1 rough and uneven and in Fig. 2.3 outside of stem smooth and even