Transpiration + translocation

Transpiration + translocation

1. Transpiration

   • Loss of water vapour from aerial part of a plant
   • Inevitable process of photosynthesesis.
     • Stomata are open for gaseous exchange
   • Osmosis from xylem vessels to mesophyll cells
     • Evaporation mesophyll into air spaces
       • Diffusion of water vapour through stomata
   • Increase
     • No of leaves (SA)
       • Density of stomata
         • Light intensity
           • Temperature
             • Wind Speed
   • Decrease
     • Thick waxy cuticle
     • Specialised adaptions
       • Xerophytes
         • Smaller leaves
           • Thick waxy cuticle
             • Dense spongy mesophyll reduces air spaces
               • Hair on suface = moist trapped air, lower WP
                 • Sunken stomata pits = moist trapped air, lower WP
     • Humidity

2. Translocation

   • Movement of assimilates
   • Sink - removes sucrose from phloem
     • Source - releases sucrose into phloem
   • Leaf = source, sucrose produced
     • Sucrose moves to phloem, active transport
       • High to Low
         • Water moves down phloem, and contents down sieve elements
           • Contents move to sink (bud)
             • High to Low
               • Sucrose into sink via facilitated diffusion
   • H+ pumped out of companion cell
     • Ions diffuse back into companion cell, with sucrose - facilitated diffusion
       • Sucrose, HIGH TO LOW into sieve tube elements