BioNinja

Root Structure

The roots of a plant form a branched network responsible for the absorption of water and minerals from the soil

• Fibrous roots are thin and very spread out to improve absorption, but are not very effective at anchorage (more suitable for smaller plants)
  

• Tap roots possess a deeply penetrating main root with many lateral branches (can access deeper soil layers and provides better anchorage)
  

Roots possess three main tissue layers that are organised to optimise the absorption of water and dissolved solutes

• The outer epidermis is where water and minerals enter the roots and may have protrusions (root hairs) to maximise surface area
  

• The middle layer (cortex) facilitates water movement between loosely packed cells and also functions as a storage site for starch
  

• The innermost layer is the vascular tissue (phloem and xylem), which allows for the transport of materials to other parts of the plant
  

Root Cross-Section

Root Anatomy

The tissues in a root are specifically distributed to maximise the absorption and transport of water and minerals

• The epidermis may have protrusions called root hairs to increase the available surface area for material absorption
  

• The cells in the cortex are loosely packed to enable the movement of water between the intercellular spaces
  

• The vascular bundle is surrounded by cells with a modified cell wall (casparian strip) that is impermeable to water 
  

  • This forces water to move into the cells to access the vascular bundle, facilitating greater control of water movement
    

Root Tissue Distribution

Root Histology

Plan Diagram

The stem of a plant functions to support and elevate the leaves, flowers and fruits (promoting photosynthesis and seed dispersal)

• Material is transported between the leaves and the roots via vascular bundles that traverse the length of the stem
  

Stems possess three main tissue layers that are organised to optimise the transport of water and nutrients between leaves and roots

• The epidermis covers the outer surface and functions to waterproof and protect the stem from damage
  

• The inner ground tissue (cortex and pith) assists in the storage of nutrients – it is also responsible for lateral growth
  

• In dicotyledons, the vascular tissue is arranged into concentric bundles around the outer edge of the stem
  

Stem Cross-Section

Stem Anatomy

The tissues in a stem are specifically distributed to support the weight of the plant and facilitate material transport

• Stems are normally divided into nodes that are capable of axillary growth (branching) and lateral growth (thickening)
  

• The epidermis in woody plants is eventually replaced by a secondary tissue (periderm) that forms bark
  

• The cells in the cortex typically have large, central vacuoles that allow the stem to store nutrients and regulate material transport
  

• The vascular bundles form a concentric ring near the outer edge of the stem to resist stem compression and bending 
  

  • The xylem is located to the interior side of the bundle and the phloem is on the exterior side (phloem = outside)
    

Stem Tissue Distribution

Stem Histology

Plan Diagram