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

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

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

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

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