A-LevelBiologyCell structure9700/33 · May/June 2017 · Q222 Marks
K1 is a slide of a stained transverse section through a plant root. You are not expected to be familiar with this specimen. You are required to: • use the eyepiece graticule to measure across the root • use these measurements to calculate the length of the cortex as a percentage of the diameter of the root • draw a plan diagram of half of the root.
- (a)(i)Use the eyepiece graticule in the microscope to measure across the diameter of the root as shown in Fig. 2.1: L to Q = ................................... eyepiece graticule units L to M = ................................... eyepiece graticule units M to N = ................................... eyepiece graticule units N to Q = ................................... eyepiece graticule units.[3]
- (a)(ii)Use the measurements from (a)(i) to state: the length across the diameter of the root (L to Q) ................................... eyepiece graticule units the length of cortex across the diameter ................................... eyepiece graticule units Calculate the length of cortex as a percentage of the diameter of the root. You may lose marks if you do not show your working. answer = ................................................%[3]
- (a)(iii)Use a sharp pencil for drawing. Use the measurements from (a)(i) to help you draw a large plan diagram of half of the root on K1, shown by the shaded area in Fig. 2.2. 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)(iv)Observe the central tissue in the root on K1. These cells are not identical. Select one group of four adjacent (touching) cells which show some of the differences between these cells. Each cell must touch at least two of the other cells. Make a large drawing of this group of four cells. Use one ruled label line and label to identify the cell wall of one cell.[5]
- (b)(i)Use a sharp pencil for graphs. Complete and plot the graph of the data shown in Table 2.1.[4]
- (b)(ii)Explain, using your knowledge of adhesion and cohesion, how water is transported through the xylem vessel elements in a tree with transpiring leaves.[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 (May/June 2017). The mark or mark type is shown in brackets.
- [3] 1 states 4 measurements (L to Q, L to M, M to N, N to Q) ;
- 2 M to N lowest value;
- 3 measurements of L to Q equal to sum of other measurements ;
- [3] 1 correct sum of L to M and N to Q;
- 2 shows division by the measurement for L to Q multiplied by 100;
- 3 answer to the appropriate degree of accuracy;
- [5] 1 minimum size at least 90mm + at least three lines drawn ;
- 2 no cells + draws correct half of the root ;
- 3 stele drawn in correct proportion to the diameter of the root ;
- 4 draws outline of xylem correctly;
- 5 uses one label line + label to xylem ;
- [5] 1 quality of line for outer wall of cell (thin line) + minimum size at least 40mm ;
- 2 only four cells drawn + each cell touching at least two of the other cells ;
- 3 cell wall drawn as two lines close together ;
- 4 at least one cell with five sides or more ;
- 5 uses one label line + one label to cell wall;
- [4] 1 (x-axis) height/m;
- 2 scale on x-axis: 10 to 2 cm, labelled at least each 2cm + origin labelled 50 ;
- 3 correct plotting of five points with a small cross or dot in circle;
- 4 five plots joined point to point or as a line of best fit drawn as a ruled thin line;
- [2] max 2 of:
- 1 (cohesion) water molecules joined to other water molecules ;
- 2 (adhesion) water molecules joined to walls of xylem vessel elements ;
- 3 water pulled up xylem or reference to supporting column of water ;
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