Kingdom Plantae


Kingdom Plantae

  • encompasses species that are:
    • multi-cellular
    • have eukaryotic cells
    • with cellulose walls
    • photosynthesise using c'phyll contained in c'plasts
  • They also show distinct differentiation w/in cells in different parts of the plant eg. leaf cells specialised for p'syn

The two major plant groups are the Bryophytes and the Tracheophytes

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Division Bryophyta

  • represented by mosses
  • Structure:
    • lack true roots
    • lack stems and leaves
    • no vascular tissue (rely on turgor support)
    • cells organised into structure superficially similar to stems and roots
    • rhizoids water and minerals gained and lost over entire surface
      • anchor to ground
      • unable to penetrate substratum
      • no specific role in water uptake
    • leaf-like structures do not have cuticle or stomata
  • As a result of not having true roots and vascular tissue, and limited ability to reduce water loss:
    • seldom reach significant size
    • restricted to damp habitats
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Division Bryophyta (mosses)

  • Mosses produce spores in a capsule at the end of a stalk
    • lifts the spore-producing cabsule above the ground, aiding dispersal by wind
    • capsule has stomata and a cuticle, so partially protected from desiccation
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Division Tracheophyta

  • Vascular plants
  • have a vascular system of xylem (water and minerals) and phloem (sucrose and amino acids)

Two major sub-divisions: 

Ferns (pteridophytes)

Flowering plants (spermatophytes)

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Subdivision Pteridophyta (Ferns)

  • Structure:
    • true roots
    • stems 
    • leaves (typically subdivided into leaflets- pinnae)
  • possess vascular tissue- xylem (water and ion transport) and phloem (organic nutrient transport)
    • Support is by turgor w/in cells and by presence of xylem thickened by lignin (lignin creates secondary cell walls
    • vascular tissue important factor in allowing them to grow to considerable sizes
  • Can colonise dried areas than mosses due to:
    • waterproof cuticle
    • stomata (allowing fine control) 
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Subdivision Pteridophyta (Ferns)

  • In many ferms, the stem (rhizome) runs horizontally underground, with leaves the only part that extends above ground
  • Disperse spores and germinate in damp conditions - spores not highly resistant to desiccation
    • an important factor in restricting ferns to relatively damp habitats

Stem- Rhizome

Leaf- Frond

Leaflet- Pinna (pl. Pinnae)

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Subdivision Spermophyta (Flowering plants)

  • Angiosperms have flowers as reproductive structures
  • Produce seeds instead of spores
  • Variable in form - include small herbaceous plants and large trees
  • Structure: 
    • true roots
    • stems and leaves
    • waterproofed cuticle
    • stomata subject to fine control
    • vascular tissue highly developed
    • roots able to penetrate deep into ground to absorb water and minerals
  • Adaptations to terrestrial habitats:
    • root systems more complex
    • xylem much more extensive + capable of providing more support
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Subdivision Spermophyta (Angiosperms)

Note: Trees are usually over 95% xylem (wood). In older trees, most of this wood no longer transports water and has a purely supportive role.

This allows trees to reach great heights and obtain more light than other plants when growing in woodland.

  • Seeds have tough outer coat which provides protection against desicattion
    • can be dispersed into hostile environments and remain dormant but viable, eventually germinating if conditions become suitable
    • many are highly adapted for disperal by wind, animal or explosive mechanism
  • Diversity of flowering plants means diff adapted for virtually all habitats on Earth, and can be adapted for anything btwn v. moist environments (or in water- hydrophytes) to extremely dry (xerophytes)
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Height:Width Ratio

Mosses- no vascular tissue, so do not grow tall

Ferns- reach a greater height than mosses, a competitive advantage

Ferns grow tall, but stem thickness does not increase proportionally

∴ fern  height : width ratio is much greater compared to trees

Woody angiosperms (trees)reach greater height than ferns

They can increase stem thickness as height increases, as they have a layer of dividing cells (beside the cambium) between xylem and phloem in their vascular bundles 

Greater width allows trees to get taller still- having greater stability at heights

This is a competitive advantage, as it leads to more light, so greater rate of p'syn

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