Transport in Plants

• To ensure all cells receive a strong supply of the nutrients they require. Especially important as a plant must be able to transport substances up their stem (against gravity).
• Vascular system in stem

  • Consists of xylem and phloem
  • Xylem on the inside of the bundle to provide support and flexibility, phloem on the outside
  • Layer of meristem cells that produce new xylem and phloem tissue when required
• Phloem


  • Sieve tube elements transport sugars around the plant
  • Companion cells designed for active transport of sugars into tubes
  • Plasmodesmata allow flow of substances between cytoplasm of different cells
• Xylem


  • Long, continuous columns made of dead tissue, allowing transportation of water
  • Contain pits, allowing water to move sideways between vessels
  • Thickened with a tough substance, providing structural support
• Vascular system in roots

  • Consists of xylem and phloem
  • Xylem arranged in an X shape to provide resistance against force
  • Surrounded by endodermis, a water supply
• Vascular system in leaves

  • Consists of xylem and phloem
• Vascular system in the leaves

  Consists of xylem and phloem, forms the midrib and veins, involved in transport and support
• Symplastic pathway


  To be continued...
• Measure transpiration rate

  Potometer. Plant cutting is placed in a water-filled tube that contains an air bubble. Rate of transpiration is calculated by measuring the movement of the air bubble over time
• Factors affecting the rate of transpiration

  • Increased light increases transpiration
  • Increased temperature increases transpiration
  • Increased humidity decreases transpiration
  • Increased air movement increases transpiration
  • Waxy cuticle prevents transpiration
• Apoplastic pathway


  A method of osmosis through the root hair cells, where water moves through the cell walls and intercellular spaces. This pathway can only be used until water reaches the Casparian strip
• Adaptations of xerophytes that allow them to live in dry conditions

  • Small/rolled leaves
  • Densely packed mesophyll
  • Thick waxy cuticle
  • Stomata often closed
  • Hairs to trap moist air
• Mechanism of translocation

  Sucrose produced in leaves loaded into sieve tubes via active transport (requiring energy). Lowers water potential, causing water to move in from xylem. Assimilates move along the sieve tube towards areas of lower hydrostatic pressure (sink). Sucrose diffuses into surrounding cells where it is needed
• Symplastic pathway

  A method of osmosis through the root hair cells, where water moves through the cytoplasm via plasmodesmata. To begin this pathway, water must be actively transported into cells
• Adaptations of hydrophytes that allow them to live in wet conditions

  • Thin or absent waxy cuticle
  • Stomata often open
  • Wide, flat leaves
  • Air spaces for buoyancy
• Cohesion-tension theory

  Water molecules form hydrogen bonds with each other, causing them to ‘stick’ together (cohesion). The surface tension of the water also creates this sticking effect. Therefore as water is lost through transpiration, more can be drawn up the stem from the roots