Transport in Plants

• Active loading


  1. Hydrogen ions actively pumped out of companion cells using ATP

  2. Hydrogen ions diffuse down concentration gradient back into cells via co-transporter proteins

  3. Sucrose carried into cells
• Adhesion (water movement)


  • Formation of hydrogen bonds between carbohydrates in xylem vessel walls and water molecules
  • Contributes to capillarity of water and transpiration pull
• Apoplast route

  • One of two pathways for water and minerals to move across the root
  • Water moves through intercellular spaces between cellulose molecules in cell wall
• Casparian strip

  • Waterproof strip surrounding endodermal cells of root
  • Blocks apoplast pathway, forcing water through symplast route
• Cohesion (water movement)


  • Formation of hydrogen bonds between water molecules
  • Contributes to capillarity of water and transpiration pull
• Cohesion-tension theory


  Model explaining movement of water from soil to leaves in continuous stream
• Companion cells


  • Active cells of phloem located adjacent to sieve tube elements
  • Retain nucleus and organelles, produce ATP for metabolic processes in themselves and sieve tube elements
• Dicotyledonous plants


  • Plants that produce seeds containing two cotyledons
  • Have two primary leaves
• Hydrophytes


  Plants adapted to live and reproduce in very wet habitats, e.g. water lilies
• Phloem


  • Living plant transport vessel responsible for transfer of assimilates to all parts of plant
  • Consists of sieve tube elements and companion cells
• Plasmodesmata (phloem)


  • Small pores between adjacent sieve tube elements and companion cells
  • Allow communication and exchange of materials
• Potometer


  Apparatus used to measure water uptake from a cut shoot
• Root hair cells


  • Specialised cells responsible for uptake of water and minerals from soil
  • Have long hair-like extensions (root hairs) adapted as exchange surfaces
• Sieve plates


  • Perforated end walls of sieve tube elements
  • Allow plant assimilates to flow between cells unimpeded
• Sieve tube elements


  • Main cells of phloem
  • Elongated cells laid end-to-end with sieve plates between
  • Contain few organelles
• Sinks (plants)


  Regions of plant that remove assimilates, e.g. roots, meristem, fruits
• Sources (plants)


  Regions of plant that produce assimilates, e.g. leaves, storage organs
• Symplast route


  • One of two pathways for water and minerals to move across root
  • Water enters cytoplasm through plasma membrane and moves between adjacent cells via plasmodesmata
  • Water diffuses down water potential gradient by osmosis
• Translocation


  Movement of organic compounds in phloem, from sources to sinks
• Transpiration


  • Water loss from plant leaves and stems via diffusion and evaporation
  • Rate affected by light, temperature, humidity, air movement, soil-water availability
• Transpiration stream


  Flow of water from roots to leaves in plants, where it is lost by evaporation to environment
• Vascular bundle


  • Vascular system in herbaceous dicotyledonous plants
  • Consists of xylem and phloem transport vessels
• Vascular system


  Network of transport vessels in animals and plants
• Xerophytes


  Plants adapted to live and reproduce in dry habitats with low water availability, e.g. cacti and marram grass
• Xylem


  Non-living plant transport vessel responsible for transfer of water and minerals from roots to shoots and leaves