Edexcel International A Level Biology

Revision Notes

4.6 Core Practical 7: Identifying Tissue Types Within Stems

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Identifying Tissue Types Within Stems

  • In order to identify tissue types within stems, a permanent pre-prepared slide could be used
  • Alternatively, a section of a plant stem could be cut and stained before preparing a temporary slide

Apparatus

  • Plant stem
  • Scalpel
  • Suitable stain
  • Microscope slide
  • Cover slip
  • Forceps
  • Dissecting needle
  • Light microscope
  • Gloves

Method

  1. Cut a very thin cross-section of the stem using a scalpel
  2. Carefully transfer each section into a dish containing a suitable stain and leave for one minute
    • A stain such as toluidine blue O (TBO) will make xylem and sclerenchyma fibres appear blue-green, while phloem will appear pinkish purple
  3. Rinse off each section in water and mount onto a microscope slide, before adding a cover slip (take care to lower the coverslip slowly over the sample from one side to the other to avoid trapping air bubbles, which can then be mistaken for plant tissues/structures)
  4. View under a microscope and adjust the focus to form a clear image
  5. Make a labelled drawing of the positions of the xylem vessels, phloem sieve tubes and sclerenchyma fibres

tissue-types-in-a-stem

Light microscope image showing tissue types (sclerenchyma fibres, phloem sieve tubes and xylem vessels) found within plant stems and their locations relative to one another

Plan diagrams

  • When drawing tissue plan diagrams you need to:
    • Read the instructions carefully
    • Draw a large diagram
    • Use a sharp pencil and do not shade (including the nucleus)
    • Use clear, continuous lines (no sketching)
    • When using an eyepiece graticule, use it to ensure you have correct proportions or if you are not using a microscope then endeavour to keep the proportions between tissues to scale
  • If drawing from a low-power image:
    • Do not draw individual cells
    • Read the question carefully as you may only have to draw a portion of the image
    • Include the magnification on the drawing
  • If drawing from a high-power image:
    • Draw only a few of the required cells
    • Draw the cell wall of the plant cells 
    • Include the magnification on the drawing
  • When labelling, remember:
    • Use a ruler for label lines (and scale lines if appropriate)
    • Label lines should stop exactly at the structure (do not use arrows)
    • Don't cross label lines over each other
    • Label all tissues and relevant structures that are requested

Transverse sections_Stems, roots and leaves (root)

A tissue plan diagram of a dicotyledonous root indicating different tissue types

Transverse sections_Stems, roots and leaves (stem)

A tissue plan diagram of a dicotyledonous stem indicating different tissue types

Transverse sections_Stems, roots and leaves (leaf)

A tissue plan diagram of a dicotyledonous leaf indicating different tissue types

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Marlene

Author: Marlene

Marlene graduated from Stellenbosch University, South Africa, in 2002 with a degree in Biodiversity and Ecology. After completing a PGCE (Postgraduate certificate in education) in 2003 she taught high school Biology for over 10 years at various schools across South Africa before returning to Stellenbosch University in 2014 to obtain an Honours degree in Biological Sciences. With over 16 years of teaching experience, of which the past 3 years were spent teaching IGCSE and A level Biology, Marlene is passionate about Biology and making it more approachable to her students.