A-LevelBiologyCell structure9700/33 · May/June 2025 · Q218 Marks

L1 is a slide of a stained transverse section through a plant organ. [Figure 2.1] is a diagram of a stage micrometer scale that is being used to calibrate an eyepiece graticule. One division, on either the stage micrometer scale or the eyepiece graticule, is the distance between two adjacent lines. The length of one division on this stage micrometer is 0.1 mm. 0 10 20 30 40 50 60 70 80 90 100 stage micrometer eyepiece graticule [Figure 2.1] [Figure 2.2] is a photomicrograph of a stained transverse section of the same plant organ as the section on L1 but from a different plant. This was taken using the same microscope and eyepiece graticule as in [Figure 2.1]. The eyepiece graticule scale has been placed across one of the larger sections of vascular tissue, labelled T in [Figure 2.2]. T. D 0 10 20 30 40 50 60 70 80 90 100 [Figure 2.2] [Figure 2.3] is the same photomicrograph as that shown in [Figure 2.2]. D [Figure 2.3]

(a)(i)Draw a large plan diagram of a region of the organ on L1 to include the epidermis and two vascular bundles. Use a sharp pencil. Use one ruled label line and label to identify the phloem.[5]
(a)(ii)Observe the xylem on the section of the plant organ on L1. Select a line of four adjacent xylem vessel elements. Each xylem vessel element must touch at least one of the other xylem vessel elements. Make a large drawing of this line of four xylem vessel elements. Use one ruled label line and label to identify the lumen.[5]
(b)(i)Use [Figure 2.1] to calculate the actual length of one eyepiece graticule unit. Show your working and give your answer in micrometres (μm). actual length = μm[2]
(b)(ii)Use the calibration of the eyepiece graticule unit from (b)(i) to calculate the actual length of the section of vascular tissue T in [Figure 2.2]. Show your working and use appropriate units. actual length of the vascular tissue T =[2]
(c)(i)Identify three observable differences, other than colour, between the section on L1 and the section in [Figure 2.3]. Record these three observable differences in Table 2.1. Table 2.1 feature L1 Fig. 2.3[3]
(c)(ii)Identify the plant organ on L1 and in [Figure 2.3]. State how one observable feature helped you to identify the plant organ. plant organ[1]

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Mark scheme

Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.

[1] 1 uses most of the available space ;
[1] 2 correct number of tissues and no cells;
[1] 3 epidermis drawn as two lines close together;
[1] 4 draws at least one vascular bundle divided into three areas;
[1] 5 label line to phloem and label to identify the phloem ;
[1] 1 lines are continuous, thin and sharp and no shading;
[1] 2 draws a line of four xylem vessel elements and each touches at least one other xylem vessel element ;
[1] 3 cell wall drawn as two lines ;
[1] 4 at least two vessel elements drawn with more than four sides;
[1] 5 label line and label to identify the lumen ;
[1] 1 shows division of 100 by 40;
[1] 2 correct answer (e.g. 2.5μm);
[1] 1 states the correct number of eyepiece graticule units along the section of vascular tissue T ;
[1] 2 multiplies this number of eyepiece graticule units by the answer in (b)(i);
[1] any three (differences) from : feature L1 Fig. 2.3 shape of organ round rectangular / irregular ; position of vascular bundles in a ring near the epidermis scattered ; sizes of the vascular bundles all are a similar size large and small sizes ; arrangement of xylem vessels in lines scattered ;
[1] correct identification of plant organ as a stem and correct observable feature that helped identification e.g. vascular bundles are in a ring near the epidermis on L1 ;

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