Transport in Plants

• Xylem

  Transports water through plants from the roots in transpiration
• Phloem

  Transports sugars and food nutrients in translocation
• Xylem

  • Made from hollowed-out dead cells that have the ends removed to make a tube for water to pass through
• Phloem

  • Made of living cells
• Water uptake

  1. Root hair cells take up water via osmosis

  2. Water moves into root cortex cells by osmosis

  3. Water enters xylem vessel

  4. Water drawn up stem to leaves

  5. Water diffuses into mesophyll cells
• Root hair cells


  • Large surface area to increase rate of osmosis and ion uptake
  • Thin wall to shorten diffusion distance
• Transpiration


  Loss of water vapour from mesophyll cell surface due to evaporation, exiting plant via stomata
• Water loss not replaced

  Plant begins to wilt as water moves out of cells and turgor pressure decreases
• Plant closes stomata


  To limit water loss
• Transpiration pull


  Water molecules drawn up xylem, not by osmosis
• Water molecules


  • Cohesive, stick together
• As water evaporates at leaf and diffuses out of stomata


  More water is drawn up the plant from the roots
• Higher temperature


  Water evaporates more easily, increasing rate of transpiration
• Higher humidity


  Decreases rate of transpiration as concentration gradient of water vapour is lower
• Translocation


  Transport of amino acids and sucrose in phloem vessels
• Source


  Areas where amino acids and sucrose are produced
• Sink


  Regions where amino acids and sucrose are stored or used for respiration and growth
• Materials are always transported from source → sink
• Leaves can act as both source and sink within a plant's life
• Transpiration definition 


  The evaporation of water from the aerial parts of a plant on the surface of the mesophyll cells which is followed by diffusion of water vapour through the stamata