A-LevelBiologyBiological molecules9700/33 · Feb/Mar 2020 · Q218 Marks
Starch grains from different types of plant differ in size and shape. Some starch grains have rings on their surfaces. You will now observe and draw starch grains from one type of plant. 1. Put one clean and dry microscope slide onto a paper towel. 2. Using a pipette, put a few drops of S onto the slide. S is a suspension of starch grains. 3. Cover the drops of S on the slide with a coverslip and use a paper towel to remove any excess suspension. 4. Use the microscope to find and observe the starch grains on the slide. You may need to reduce the amount of light entering the microscope and adjust the fine focus to observe the starch grains clearly. 5. Select, from a single field of view, four starch grains that show different sizes and features.
- (a)(i)Make a large drawing of the four starch grains that you have selected.[4]
- (a)(ii)Use the diagrams in Fig. 2.1 to identify which of the starch grains, J, K, L or M, matches most closely the starch grains drawn in (a)(i). answer[1]
- (a)(iii)Find the mean image length of the three starch grains drawn by the student, along the lines shown in Fig. 2.2. Show all the steps in your working and use appropriate units. mean image length =[2]
- (a)(iv)When viewed using the microscope, the student found that starch grain N1 measured 4 eyepiece graticule units along the position of the line drawn in Fig. 2.2. Use this information and your answer to (a)(iii) to calculate the mean actual length of the three starch grains in Fig. 2.2. Show all the steps in your working and use appropriate units. mean actual length =[2]
- (b)Draw a large plan diagram of the transverse section of the whole root shown in Fig. 2.3. Use one ruled label line and label, with the letter G, the tissue that contains most of the starch grains.[5]
- (c)Prepare an appropriate table so that it is suitable for you to record the observable differences between the root in Fig. 2.4 and the root in Fig. 2.5. Record the observable differences, other than differences in colour, in your table.[4]
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 (Feb/Mar 2020). The mark or mark type is shown in brackets.
- [1] suitable size and lines continuous, thin and sharp ; [2] draws only four starch grains ; [3] shows details of surface markings; [4] draws single line around each grain;
- [1] L;
- [1] measures and records the length of three starch grains using the lines N1, N2 and N3 and units ; [2] shows the addition of these three lengths and shows division by three ;
- [1] correct actual length of N1 = 64 µm ; 4 × 16 μm [2] uses answer to (a)(iii) and shows how to calculate mean actual length of the three starch grains ; (64 image length of N1) × mean image length from (a)(iii)
- [1] suitable size and whole root drawn ; [2] draws at least three layers of tissue ; [3] shows correct proportion of the stele to the diameter of the root ; [4] vascular tissue subdivided ; [5] label line and label G to the cortex ;
- [1] organises comparison into table with three columns with first column for feature and records only differences or organises comparison into table with two columns with direct comparison of the same feature in each row and records only differences ; [2, 3 and 4] three correct differences;;; e.g. feature: amount of vascular tissue, Fig. 2.4: large(r) amount of vascular tissue, Fig. 2.5: small(er) amount of vascular tissue; feature: cortex size, Fig. 2.4: small(er) cortex, Fig. 2.5: large(r) cortex; feature: starch grains, Fig. 2.4: starch grains present, Fig. 2.5: starch grains absent; feature: number of layers, Fig. 2.4: many / more, Fig. 2.5: few / fewer; feature: shape of cortex cells, Fig. 2.4: rectangular/longer / flatter / elongated cells, Fig. 2.5: circular/round / oval; AVP; AVP
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