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A-LevelBiologyTransport in plantsMay/June 2020Paper 3 Q218 Marks

Water moves through xylem vessel elements in plants. The diameter of xylem vessel elements varies between different species of plant. You will measure how quickly coloured water moves through xylem vessel elements of different diameters. You will use microscope slides to represent xylem vessel elements of different diameters. You are provided with the materials shown in Table 2.1. Table 2.1 labelled description hazard P container with 6 pieces of paper none R beaker containing coloured water none Carry out step 1 to step 9. 1. Put one clean, dry microscope slide on the bench. 2. Put two pieces of paper from the container labelled P on top of the microscope slide. 3. Put another microscope slide on top of the paper. 4. Put tape around the two microscope slides to hold them together as shown in [Figure 2.1A]. 5. Label this pair of microscope slides, A. 6. Repeat step 1 to step 4 using four pieces of paper instead of two pieces of paper, as shown in [Figure 2.1B]. 7. Label this pair of microscope slides, B. 8. Hold A by the side edges and remove the paper. You should be left with a gap as shown in [Figure 2.2]. 9. Repeat step 8 for B. 10. Put A into the beaker labelled R, as shown in [Figure 2.3]. Start timing immediately and record in Table 2.2 the time it takes for the coloured water to reach the top of the pair of microscope slides. If the time taken is longer than 60 seconds record the result as 'more than 60'. 11. Repeat step 10 using B instead of A. Fig. 2.4 is a photomicrograph of a stained transverse section through a leaf. You are not expected to be familiar with this specimen. [Figure 2.4] Use a sharp pencil for drawing. You are expected to draw the correct shape and proportions of the different tissues. Fig. 2.5 is a photomicrograph of a stained transverse section through a leaf of a different type of plant. You are not expected to be familiar with this specimen. [Figure 2.5] Fig. 2.6 is the same photomicrograph as in Fig. 2.5 but with line Z added to show the diameter of the vascular bundle. [Figure 2.6]

📋 Examiner Report & Trap Analysis

Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...

🎯 Mark Scheme Breakdown

Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.

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About This A-Level Biology Question

Topic

This structured question tests Transport in plants in A-Level Biology (syllabus code 9700). It is worth 18 marks.

Source

This question appeared in the Cambridge A-Level Biology May/June 2020 examination, Paper 3 Variant 2.

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