3.1.3. Transport in plants

• Translocation movement of assimilates (products of photosynthesis but sucrose and not glucose as to easily broken down by respiration) from source to sink
• Phloem leads by the apoplast pathway so requires energy released in the form of ATP via respiration, this is why the tissue is alive and the companion cell
• apoplast pathway

  1. H+ pumped out of cc through H+ pumps by active transport so the conc is higher outside CC
  2. electrochemical gradient so H+ comes back using cotransporter proteins with sucrose, increasing conc in cc
  3. as the water potential is lower in cc cell so diffuse through the plasmodesmata into the sieve tube, lowering the so in ste so water moves out of cc into ste, increasing turgo pressure for mass flow
• 1. .
  2. mass low as assimilates move from source to sink down a pressure gradient
  3. phloem unloading, passive. diffuse from phloem to sinks. to maintain conc gradient sucrose is converted into other forms. loss of assimilates increases so in ste so h20 moves out of cell via osmosis or enters xylem transpiration stream
• symplast pathway; through cytoplasm (diffusion) and plasmodesmata (osmosis)

  apoplast pathway; through cell wall using tension

  uses this to move from root hair cells to do dermis to epidermis and cortex
• water moves across the endodermis

  • apoplast pathway until it meets the casperian strip which has subrin making it waterproof so must move symplast pathway, forcing it to go through the plasma membrane. happens so water and mineral ions in and toxins do not enter
• • ions move from endodermis to xylem first, decreasing the wp so water moves via osmosis down a wp gradient
  • this creates root pressure and forces water going upwards