A-LevelBiologyTransport in plants9700/31 · May/June 2017 · Q219 Marks

J1 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 J1 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 two smaller outer vascular bundles • only one larger inner vascular bundle • 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.[5]
(a)(ii)Observe the cells of the epidermis on J1. Select one group of four adjacent (touching) cells in the epidermis. Do not select guard cells in the epidermis. Each cell must touch at least one of the other cells. Use the eyepiece graticule in the microscope to measure, as shown in Fig. 2.1: • the total length of the four cells, L • the depth of one of the cells, T. L = .......................... eyepiece graticule units T = .......................... eyepiece graticule units[2]
(a)(iii)Use the measurements from (a)(ii) to help you make a large drawing of this group of four cells on J1. Use one ruled label line and label to identify the cell wall of one cell.[5]
(a)(iv)Suggest one observable feature of J1 which supports the conclusion that this plant exchanges gases through its stem.[1]
(b)Fig. 2.2 is a photomicrograph of a stained transverse section through a different type of plant stem. You are not expected to be familiar with this specimen. Calculate the magnification of Fig. 2.2 using the scale bar. You may lose marks if you do not show your working or if you do not use appropriate units. magnification × ..........................[3]
(c)Annotate Fig. 2.2 to describe three observable differences between the stem sections in Fig. 2.2 and on J1 by: • drawing label lines to three features in Fig. 2.2 that show these differences • describing next to each line how each feature is different from the specimen J1.[3]

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] 1 minimum size at least 80 mm + at least 3 vascular bundles drawn ;
2 no cells + only three vascular bundles + epidermis ;
3 outer vascular bundles smaller than inner vascular bundles ;
4 decides to subdivide vascular bundle into at least two areas;
5 uses one label line + one label to xylem ;
[2] 1 measurements for both L and T;
2 L at least 3 times larger than T;
[5] 1 quality of line for outer wall of cells (thin line) + minimum size at least 40mm across largest cell + no shading;
2 only four cells drawn, each cell touching at least one other cell;
3 correct proportions of depth to length of epidermal cells using measurements in (a)(ii) ;
4 cells drawn with upper convex walls ;
5 uses one label line + one label to cell wall ;
[1] many stomata or large air spaces;
[3] 1 shows multiplication by 1000 to convert measurement from mm to m ;
2 displays number divided by 1460;
3 correct answer ;
[3] any 3 correct differences annotated on Fig 2.2 ;;;