A-LevelBiologyCell structure9700/33 · Oct/Nov 2018 · Q221 Marks

K1 is a slide of a stained transverse section through a plant leaf. You are not expected to be familiar with this specimen. Use a sharp pencil for drawing.

(a)(i)Select a field of view so that you can observe the different tissues in the whole leaf. Draw a large plan diagram to show the observable tissues in the whole leaf. Use one ruled label line and label to identify the palisade tissue. You are expected to draw the correct shape and proportions of the different tissues.[5]
(a)(ii)Observe the epidermis with trichomes (hairs) in K1. Select three adjacent, touching epidermal cells where only one cell has a trichome attached. Make a large drawing of these epidermal cells and the trichome. Use one ruled label line and label to identify a cell wall of one cell. You are expected to draw the correct shape and proportions of the different cells.[5]
(a)(iii)The presence of trichomes supports the conclusion that the plant grows in a dry environment. Observe the leaf on K1. Suggest one other observable feature in the specimen on K1 which supports this conclusion. Explain how this feature would prevent water loss. feature explanation[2]
(b)[Figure 2.1] shows a photomicrograph of part of a leaf surface showing the stomata. Estimate the number of stomata inside the square shown on [Figure 2.1]. Show on [Figure 2.1] those stomata that you counted. If half or more of a stoma is within the square, count it as a whole stoma. Do not count any stoma that is less than half within the square. estimated number of stomata[3]
(c)(i)A scientist investigated the percentage of stomata that were open between the times of 00:00 and 12:00. Table 2.1 shows the results for this investigation. Table 2.1 time of day | percentage of open stomata ---|--- 00:00 | 17 02:30 | 9 05:00 | 78 09:00 | 79 12:00 | 89 Plot a graph of the data shown in Table 2.1 on the grid in [Figure 2.2]. Use a sharp pencil for drawing graphs.[4]
(c)(ii)Suggest the effect that the change in percentage of open stomata between 02:30 and 05:00 would have on the rate of transpiration. Explain your answer.[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 (Oct/Nov 2018). The mark or mark type is shown in brackets.

[5] mp 1 drawing of a minimum size with a minimum number of tissue layers and no cells drawn ;
[5] mp 2 whole leaf drawn ;
[5] mp 3 correct leaf shape with at least three layers of tissue ;
[5] mp 4 correct position of vascular bundle;
[5] mp 5 uses label line and label to identify the palisade tissue ;
[5] mp 1 drawing of a minimum cell size and drawn with thin, continuous lines;
[5] mp 2 draws three touching epidermal cells and a trichome ;
[5] mp 3 two lines drawn around each cell;
[5] mp 4 draws trichome or epidermal cell with an inclusion;
[5] mp 5 uses label line and label to identify the cell wall ;
[2] mp 1 suggests a suitable feature such as the rolled leaf;
[2] mp 2 explanation of how feature prevents water loss such as traps moisture ;
[3] mp 1 shows evidence of counting whole stomata on Fig. 2.1;
[3] mp 2 shows evidence of counting half stomata on Fig. 2.1;
[3] mp 3 correct number of stomata within range;
[4] mp 1 x-axis: time of day, y-axis percentage of open stomata ;
[4] mp 2 scale on x-axis: 2 to 2 cm scale, on y-axis is 20.0 to 2 cm labelled each 2 cm;
[4] mp 3 correct plotting of five points with small cross or dot in circle;
[4] mp 4 plots joined point to point with thin line;
[2] mp 1 explains that between 02:30 and 05:00 more stomata open and the rate of transpiration increases ;
[2] mp 2 more evaporation of water and faster diffusion ;