Plants

• Vascular plant


  Plant composed of cells, tissues, and organs

  
• Basic vascular plant organs

  • Roots
  • Stems
  • Leaves

  
• Roots

  • Anchor vascular plant in soil
  • Absorb minerals and water
  • Often store carbohydrates and other reserves
• Tall plants


  • Generally have a taproot system - one main vertical root, the taproot
• Small vascular plants


  • Efficiently anchored by a fibrous root system - a thick mat of slender roots spreading out below the soil surface
• Absorption of water and minerals occurs primarily near the tips of elongating roots, where root hairs emerge and increase the surface area

  
• Most root systems form mycorrhizal associations, symbiotic interactions with soil fungi that increase a plant's ability to absorb minerals
• Evolutionary adaptations of roots

  • Anchoring
  • Absorption
  • Storage
  • Symbiosis
  • Reproduction
• Stems


  • Bear leaves and buds
  • Chief function is to elongate and orient the shoot to maximize photosynthesis by the leaves

  
• Nodes


  Points at which leaves are attached
• Internodes


  Stem segments between nodes
• Apical bud


  Near the growing shoot tip
• Axillary bud


  Form a lateral branch or, in some cases, a thorn or flower
• Modified stems


  • Rhizomes
  • Stolons
  • Tubers

  
• Leaves


  • Main photosynthetic organ
  • Exchange gases with the atmosphere
  • Dissipate heat
  • Defend against herbivores and pathogens
• Petiole


  Stalk that joins the leaf to the stem at a node
• Leaf shape


  • Simple versus compound

  
• Compound leaves may withstand strong wind with less tearing and confine some pathogens to a single leaflet
• Leaf adaptations


  • Support
  • Protection
  • Storage
  • Reproduction

  
• Plant tissue systems


  • Ground tissue
  • Dermal tissue
  • Vascular tissue

  
• Ground tissue


  • Fills the spaces between more specialized cell types
  • Important sites of photosynthesis, respiration & storage
• Vascular tissue


  • Xylem & Phloem form a continuous distribution system embedded in the ground tissue of shoots & roots
  • Vascular bundle - strand of tissue containing xylem & phloem

  
• Dermal tissue


  • Covers the plant
  • Consists of the epidermis, a single layer of tightly packed, flat, transparent parenchyma cells
  • Contains cuticle, stomata, and guard cells

  
• Ground tissue cell types

  • Parenchyma
  • Collenchyma
  • Sclerenchyma

  
• Parenchyma


  • Most abundant
  • Vital functions: photosynthesis, respiration, gas exchange & starch storage
• Collenchyma


  Provide elastic support without interfering with the growth of young stems or expanding leaves
• Sclerenchyma


  • Inelastic support to parts of a plant that are no longer growing
  • Secondary wall contains lignin, a tough, complex molecule that adds great strength

  
• Xylem

  • Transports water & dissolved minerals from the roots to all parts of the plant

  
• Water-conducting cells in xylem

  • Tracheids
  • Vessel elements

  
• Tracheids

  • Long, narrow cells that overlap at their tapered ends
  • Water moves from tracheid to tracheid through pits, which are thin areas in the cell wall
• Vessel elements


  • Short, wide, barrel-shaped conducting cells that stack end to end, forming long, continuous tubes
  • Their side walls have pits, but their end walls are perforated or absent
• Phloem


  • The main conducting cells are sieve tube elements, which align end to end to make a single functional unit called sieve tube
  • Companion cells are specialized parenchyma cells that retain all of their organelles

  
• Determinate growth


  Shoots become larger by adding units ("modules") consisting of repeated nodes and internodes
• Indeterminate growth


  Roots can branch repeatedly as they explore the soil
• Modular growth is one key feature that distinguishes plants from animals
• Types of meristems


  • Apical meristems
  • Lateral meristems
• Apical meristems


  When cells divide, they give rise to new cells that differentiate into all of the tissue types
• Lateral meristems


  When the cells divide, they typically produce tissues to both the inside & outside of the meristems
• Sexual reproduction produces genetically variable offspring, increasing reproductive success in a changing environment
• Asexual reproduction produces identical clones that develop from the roots, stems, or leaves of a parent plant