A-LevelBiologyTransport in plants9700/31 · Oct/Nov 2024 · Q218 Marks

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

(a)(i)Draw a large plan diagram of the region of the leaf on J1 indicated by the shaded area in Fig. 2.1. Use a sharp pencil. Use one ruled label line and label to identify the lower epidermis. draw this region [Fig. 2.1][5]
(a)(ii)Observe the xylem vessel elements in the leaf on J1. Select a line of four adjacent xylem vessel elements. Each xylem vessel element must touch at least one other xylem vessel element. • Make a large drawing of this line of four xylem vessel elements. • Use one ruled label line and label to identify the wall of one xylem vessel element.[5]
(b)(i)Identify three observable differences, other than colour, between the section on J1 and the section in Fig. 2.2. Record these three observable differences in Table 2.1.[3]
(b)(ii)Fig. 2.3 shows a diagram of a stage micrometer scale that is being used to calibrate an eyepiece graticule. The length of one division on this stage micrometer is 0.2 mm. Use Fig. 2.3 to calculate the length of one eyepiece graticule unit. Show your working. Include the unit in your answer. length of one eyepiece graticule unit =[3]
(b)(iii)Fig. 2.4 shows the same eyepiece graticule and same lenses being used to measure the width of the section shown in Fig. 2.2. Use your answer in (b)(ii) to calculate the actual width of the section shown in Fig. 2.4. Show your working. actual width of the section[2]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2024). The mark or mark type is shown in brackets.

[5] 1 uses most of the available space and no shading;
[5] 2 draws the correct region of the leaf and no cells included ;
[5] 3 draws the correct proportion of palisade layer in proportion to depth of leaf ;
[5] 4 draws area under vascular bundle or subdivision of the vascular bundle;
[5] 5 label line and label to the lower epidermis ;
[5] 1 uses most of the available space and lines continuous, thin and sharp ;
[5] 2 draws only four xylem vessel elements and each vessel touches at least one other vessel ;
[5] 3 two lines around each vessel and three lines where cells touch ;
[5] 4 draws correct shape of cells with 4 or 5 sides;
[5] 5 label line and label to wall of one xylem vessel element ;
[3] differences between J1 and Fig. 2.2 ; ; ; any three from : (feature) thickness of palisade layer J1 thick Fig. 2.2 thin ; (feature) endodermis J1 not visible Fig. 2.2 present and distinct ; (feature) shape of vascular bundles J1 circular Fig. 2.2 double / 2 regions ; (feature) size of mid-rib J1 smaller Fig. 2.2 larger ;
[3] 1 states 10 eyepiece graticule units in 0.2 mm ;
[3] 2 divides 0.2 by 10;
[3] 3 correct answer and appropriate units (µm or mm);
[2] 1 states the correct number of eyepiece graticule units across width of section;
[2] 2 shows 75 multiplied by the answer to (b)(ii) ;

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