Xylem, phloem and sclerenchymaEdexcel International A Level Biology: Subtopic test

1. 1
   A student examines a stained transverse section of a young sunflower stem using a light microscope. The vascular bundles form a ring near the outside of the stem, and each bundle contains xylem, phloem and a cap of sclerenchyma fibres.

   (a)

   Ignoring the cambium, which sequence shows the tissues of one vascular bundle from the centre of the stem outwards?

   [1 mark]

   • APhloem, xylem, sclerenchyma fibres
   • BSclerenchyma fibres, phloem, xylem
   • CXylem, phloem, sclerenchyma fibres
   • DXylem, sclerenchyma fibres, phloem

   (b)

   Which feature is found in a mature xylem vessel but not in a phloem sieve tube element?

   [1 mark]

   • ALignified cell walls
   • BLiving cytoplasm
   • CSieve plates at the end walls
   • DA companion cell alongside

   (c)

   Describe two differences in structure between a xylem vessel and a phloem sieve tube element.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student prepares temporary slides of sections cut from the root, stem and leaf of a plant to compare the tissues. The sections are stained with toluidine blue, which stains lignified walls blue-green and unlignified cellulose walls pink or purple. The student wants to identify the tissues and to measure their dimensions.

   (a)

   The student wants to find the real diameter of a xylem vessel from the eyepiece graticule. What must be done first?

   [1 mark]

   • AUse each graticule division as 1 µm
   • BCount the number of cells across the vessel
   • CUse the low-power calibration at every magnification
   • DCalibrate the graticule against a stage micrometer for the objective lens in use

   (b)

   Which pair of tissues in the stem section would stain blue-green with toluidine blue?

   [1 mark]

   • APhloem sieve tubes and companion cells
   • BXylem vessels and sclerenchyma fibres
   • CPhloem sieve tubes and sclerenchyma fibres
   • DXylem vessels and phloem companion cells

   (c)

   Describe two steps the student should take to make a temporary slide of a stem section that is suitable for identifying the tissues.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A teacher describes three types of cell from a plant stem. Cell P is long and dead, with a very narrow lumen and thick lignified walls. Cell Q is a dead, hollow tube with a wide lumen, lignified walls with small pits, and no end walls between neighbouring cells. Cell R is a living cell with thin cellulose walls, perforated end walls and almost no cytoplasm, and it lies next to a cell with dense cytoplasm.

   (a)

   Identify cells P, Q and R and state one main function of each.

   [3 marks]

   (b)

   Explain how the structure of cell Q suits it to its function and how the structure of cell R, with its neighbouring cell, suits it to its function.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student studies a young dicotyledonous stem. The vascular bundles lie in a ring near the edge of the stem. The student will compare the support tissues and transport tissues in the bundles, and then prepare a fresh section of the stem for a microscope.

   (a)

   Compare the structure, position and function of xylem vessels and sclerenchyma fibres in the stem.

   [6 marks]

   (b)

   Describe how the student should prepare and observe a transverse section of the fresh stem so that the tissues can be identified, drawn and measured.

   [6 marks]

   Total for question 4: 12 marks

End of questions