Translocation of sucrose

• Define translocation

  it is the movement of sucrose in the phloem
• the phloem consists of..

  lots and lots of sieve tube elements, it has no space for organelles so all the sieve tube organelles are found in the companion cell
• Source

  the source is what makes sucrose, which is the leaf cell
• Sink

  It either stores sucrose or uses it in respiration, it is the root cell
• Stage 1 in translocation of sucrose- IN THE LEAF CELL

  The source (leaf cell) It contains chloroplast, this is the site of photosynthesis, it creates sucrose. The sucrose then moves into the companion cell by facilitated diffusion, using a carrier protein and down it's concentration gradient.
• Stage 2- Translocation of sucrose: IN THE COMPANION CELL

  There is a lower concentration of sucrose in the companion cell and there is a higher concentration of sucrose in the phloem, so the sucrose is moved into the phloem via active transport, it requires ATP. This lowers the water potential of the phloem.
• Stage 3- Translocation of sucrose: IN THE PHLOEM

  The water potential of the phloem has been lowered, next to the phloem is a xylem vessel that has a continuous column of water, so the water is moved into the phloem via osmosis. This increases the hydrostatic pressure in the phloem. The sucrose then moves down a pressure gradient near the sink cell (root cell).
• Stage 4- translocation of sucrose: THE SINK CELL

  the sucrose is actively transported from the sieve tube elements in the phloem to the sink cell (root cell) this lowers the water potential of the root cell. So water is moved from the phloem into the root cell via osmosis. So water is also moved into the xylem. This lowers the hydrostatic pressure of the phloem