module 4

• Functions of roots


  • Absorbs water and nutrients from the soil
  • Stores food
  • Anchors plants in place
  • Produces plant hormones
• Plant hormones produced by roots

  • Auxins
  • Gibberellins
  • Cytokinins
  • Ethylene
  • Abscisic acid
• Auxins


  • Elongation in response to stimuli
  • Apical dominance
• Gibberellins


  • Seed germination
  • Stem elongation
• Cytokinins


  • Cell division
  • Ensure same growth rate for roots and shoots
  • Growth of fruits
  • Secondary (lateral) growth
• Ethylene


  • Maturation and aging
  • Ripening of fruits
• Abscisic acid


  • Inhibits cell division
  • Death of leaves (abscission)
  • Seed dormancy
  • Stress response
  • Closing of the stomata
• Root systems


  • Taproot system
  • Fibrous root system
• Taproot system


  • Root growth of dicots and gymnosperms
  • Has large main root (taproot)
  • Penetrates deep into the soil
  • Primary root remains
  • Can store food
  • Develops from a radicle

  
• Fibrous root system


  • Root growth of monocts and seedless vascular plants
  • No large main root
  • Does not penetrate deeply into the soil (shallow)
  • Primary root does not remain
  • Cannot store food
  • Develops from the stem

  
• Root cap


  Thimble-shaped mass of parenchyma cells covering the tip of each root, protects delicate tissues, contains amyloplasts and dictyosomes

  
• Region of cell division

  Composed of apical meristem, produces the root cap, cells are cubical with large nuclei and small vacuoles, divisions are rhythmic

  
• Region of cell elongation

  Cells become longer and wider, vacuoles merge into large ones, tissues are permeable to minerals
• Region of maturation


  Cells mature and differentiate into dermal, vascular, and ground tissues, includes root hairs, cortex, and endodermis

  
• Endodermis


  Single-layered cylinder of cells with suberin-impregnated primary walls (Casparian strip), forces water and dissolved substances to pass through plasma membranes, has passage cells
• Vascular cylinder


  Core of primary phloem and xylem tissues inside the endodermis
• Pericycle


  Region where lateral roots arise, cells continue to divide even after maturation
• Specialized roots


  • Prop roots
  • Haustoria
  • Buttress roots
  • Aerial roots
  • Epiphytic roots
  • Contractile roots
  • Pneumatophores
  • Suckers

  
• Prop roots


  Elaborate set of aerial roots that provide additional support
• Haustoria


  Parasitic plant roots that penetrate host plant tissues and absorb water and minerals
• Buttress roots


  Support plants in shallow, wet soil

  
• Aerial roots


  Roots of climbing plants, may be photosynthetic
• Epiphytic roots


  Long, hanging aerial roots that eventually reach the ground and anchor the plant, often kill the original host plant
• Contractile roots


  Adjust the depth of bulbs and corms in the soil

  
• Pneumatophores


  Breathing roots produced by trees in swampy habitats to facilitate gas exchange
• Suckers


  Aboveground stems that develop from adventitious buds on the roots, become independent plants

  
• Functions of stems


  • Transport water and nutrients
  • Store food
  • Support other plant parts
  • Produce new living tissues
• Terminal bud


  Grows stems that bear leaves and flowers, located at the tip of the stem, protected by bud scales

  
• Axillary bud


  Grows stems that bear leaves and flowers, found in the axils above leaf scars

  
• Node


  Area of the stem where leaves are attached

  
• Internode


  Area on the stem between two successive nodes
• Lenticel


  Site of loosely arranged cells that allows gas exchange
• Epidermis


  Outer covering that provides protection by producing cuticle
• Cortex


  Thick cylinder of ground tissue that functions as storage, support, and photosynthesis
• Stele


  Central cylinder of the stem composed of the vascular bundle
• Vascular bundle


  Vascular cells arranged in a circular pattern, including primary phloem and primary xylem
• Pith


  Ground tissue composed of large, thin-walled parenchyma cells that function primarily for storage
• Vascular cambium


  Main growth tissue of stems and roots, divides to produce secondary xylem and secondary phloem

  
• Sapwood


  Functioning secondary xylem
• Heartwood


  Non-functioning secondary xylem that provides structural support