translocation and mass flow theory

• what direction does sugar move in a plant

  root to leaf in spring

  leaf to root in summer
• what is used to describe where sucrose moves from and to

  sources and sinks
• what is another name for mass flow theory

  pressure theory
• what are the stages of mass flow theory

  H+ ions are pumped by active transport from the companion cell into a photosynthesising cell

  H+ ions combine with the sucrose

  these diffuse back into the companion cells by co-transport

  water potential lowers in companion cell

  water enters the companion cell by osmosis creating high pressure

  sucrose and water is forced into sieve tube elements via plasmodesmata down through the phloem into the roots
• how is pressure gradient maintained in the roots

  sucrose is converted into insoluble starch

  water leaves the roots via the xylem