Syllabus Edition

First teaching 2023

First exams 2025

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Drawing Root & Stem Structure: Skills (HL IB Biology)

Revision Note

Marlene

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Marlene

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Dicotyledonous Stem Structure

Distribution of tissues in a transverse section of a dicotyledonous stem

  • The stem in a dicotyledonous plant contains several different types of tissues, which include:
    • The epidermis which forms the outer layer of the stem
      • This prevents water loss and provides protection from herbivores
    • Parenchyma which forms the cortex and pith of the stem
      • These cells act as storage structures for starch and other substances
      • The cortex is the region located directly beneath the epidermis while the pith is the central region of the stem
    • Vascular tissue arranged in a ring of vascular bundles
      • Xylem transports water and dissolved mineral ions from the roots to the leaves
      • Phloem transports organic solutes from the leaves to other parts of the plant
  • The distribution of tissues in a transverse section of a dicotyledonous stem can be represented as a plan diagram
  • There are a few things to keep in mind when drawing plan diagrams:
    • Do not draw individual cells; only the outline of different tissues are drawn
    • Draw clear, continuous lines; do not sketch
    • Avoid shading parts of your drawing
    • Pay attention to the size and proportions of different parts visible in a micrograph
    • Make sure the different parts are clearly labelled
    • Add a scale bar or the estimated size of your drawing
    • Include annotations that give the functions of the labelled sections

Transverse sections_Stems, roots and leaves (stem)

A plan diagram (bottom right) showing the distribution of different tissues in a dicotyledonous stem

Note that a hand-drawn plan diagram should not contain shading

Examiner Tip

You are expected to annotate your drawing with the main functions of these structures; this is not shown above

Dicotyledonous Root Structure

Distribution of tissues in a transverse section of a dicotyledonous root

  • The arrangement of the vascular tissues differ in a root compared to a stem
    • The xylem is centrally located in a root in a cross-shaped structure, while it forms the outer part of the ring of vascular bundles in a stem
      • Remember, x = a cross = xylem
    • Phloem bundles are arranged between the cross "arms" of xylem in a root, while it forms the inner part of the ring of vascular bundles in a stem
  • The cortex consists of parenchyma cells that store starch and other substances while the epidermis forms the outer layer of the root
    • Specialised epidermal cells called root hairs are present in roots to absorb water and mineral ions from the soil
  • The endodermis forms the boundary between the vascular tissue and cortex in a root
  • You should be able to draw a plan diagram of the tissues in a dicotyledonous root; see above for the features of a plan diagram drawing

Transverse sections_Stems, roots and leaves (root)

A plan diagram (bottom right) of a dicotyledonous root showing the distribution of different tissues

Note that hand-drawn plan diagrams should not contain any shading

Examiner Tip

Don't forget to draw your plan diagrams large enough to fill at least half of the available space on a page. Making a drawing that is too small will make it difficult to label structures accurately and may cost you marks

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Marlene

Author: Marlene

Expertise: Biology

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.