(8) transport in plants

• Xylem


  Transport water and mineral ions, support stem
• Xylem


  • Lignin provides support
  • Dead and hollow
  • Cells joined end to end, no cross walls
  • Walls are waterproof
• Phloem


  Transport sucrose and amino acids
• Phloem


  • Living tissue
  • Sieve tubes
  • Bidirectional
• Root hair cells


  Large surface area, increases uptake of water and mineral ions
• Transpiration


  Loss of water vapour from leaves, by evaporation of water at the surfaces of mesophyll cells followed by a diffusion of water vapour through stomata
• Water uptake


  1. Root hair cells (osmosis)

  2. Root cortex cells (osmosis)

  3. Xylem cohesion force between water molecules, adhesion between water molecules and side of xylem, transpiration pull pulls water up xylem

  4. Mesophyll layer (evaporates)

  5. Airspace (diffuse)

  6. Stomata (diffuse)
• Water vapour loss


  Related to large internal surface area provided by air spaces between mesophyll cells, size and number of stomata
• Factors affecting transpiration rate

  • Temperature (kinetic energy of water molecules increase, evaporate, evaporate and diffuse faster from mesophyll cells, transpiration rate increase)
  • Wind speed (wind removes away the water vapour, transpiration rate increase)
  • Humidity (air surrounding leaf has more water vapour, weak concentration gradient for diffusion, transpiration rate decreases)
• Translocation


  Movement of sucrose and amino acids in phloem from sources to sink
• Translocation


  • Sources release sucrose or amino acids
  • Sinks use or store sucrose or amino acids
• Wilting


  Water in plant keeps it turgid and helps support plant, if amount of water loss in plant is more than amount of water available in soil to travel into plants through roots, plant will become soft and droop, cell walls become flaccid, cannot support plant