A-LevelBiologyTransport in plants9700/31 · May/June 2021 · Q218 Marks

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

(a)(i)Set up the microscope so that you can observe the section on J1. Use a sharp pencil for drawing. Draw a large plan diagram of the whole section of the leaf on J1. Your drawing should show the correct shapes and proportions of different tissues. Use one ruled label line and label to identify the epidermis.[5]
(a)(ii)Observe the ring of cells surrounding the vascular tissue in the centre of the section on J1. Select a line of four adjacent cells that make up this tissue. Each cell that you draw must touch at least one of the other cells. • Make a large drawing of this line of four cells. • Use one ruled label line and label to identify the cell wall of one cell.[5]
(b)(i)[Fig. 2.1] is a photomicrograph of a stained transverse section through a leaf of a different type of plant. [Fig. 2.1] Identify the observable differences between the section on J1 and the section in [Fig. 2.1]. Record the observable differences in Table 2.1. Table 2.1 feature J1 Fig. 2.1[3]
(b)(ii)The presence of a thick waxy cuticle in the leaf section in [Fig. 2.1] supports the conclusion that the plant is adapted to live in a dry environment. Observe the leaf section in [Fig. 2.1]. Suggest one other observable feature in the section in [Fig. 2.1] which supports this conclusion. Explain how this feature would prevent water loss.[1]
(c)(i)[Fig. 2.2] is a photomicrograph of the same leaf section that is in [Fig. 2.1]. [Fig. 2.2] You will need to use the grid to find the area of the palisade layer and the total area of the leaf section in [Fig. 2.2]. Each square of the grid is 1cm². In some squares the palisade layer or the leaf section does not fill the whole square. Describe the method you will use to decide which of these squares to include.[1]
(c)(ii)State the area of the palisade layer and the total area of the leaf section in [Fig. 2.2]. area of palisade layer = cm² total area of the leaf section = cm²[2]
(c)(iii)Calculate the area of the palisade layer as a percentage of the total area of the leaf section. Show your working.[1]

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

[5] 1 uses most of the available space and no shading ; 2 no cells drawn ; 3 correct proportions of vascular bundle; 4 draws sunken stomata in the epidermis ; 5 label line and label to epidermis ;
[5] 1 uses most of the available space and all lines sharp and continuous ; 2 draws only four whole cells and each cell touches at least one other cell; 3 two lines around each cell and three lines where cells touch; 4 draws correct shape of cells ; 5 label line and label to one cell wall;
[3] records correct differences: any three of, e.g.: feature J1 Fig. 2.2 number of vascular bundles many fewer; ring of cells around vascular bundle present absent shape of stem diamond curved; trichomes absent present;
[1] trichomes / rolled leaf, and traps a layer of water vapour and reduces the water potential gradient ;
[1] count squares that are half full and more than half full and full as 1;
[2] counts and records the area of the palisade layer ; counts and records the total area of the leaf;
[1] shows area of palisade layer divided by area of leaf multiplied by 100;