Mass flow theory

• Label this diagram of the sites of mass flow theory

  A) xylem

  B) phloem

  C) companion cell

  D) source cell

  E) sink cell

  
• Explain mass flow theory.?

  1. Movement of sucrose produced by photosynthesis from source cell (palisade cell) to companion cell by facilitated diffusion
  2. Sucrose is transported from the companion cell to the phloem using ATP
  3. Water moves from xylem to phloem by osmosis. This increases hydrostatic pressure at the top of the phloem
  4. Sucrose is actively transported from the phloem to the companion cell
  5. Water moves from the phloem into the companion cell by osmosis, and some water is reabsorbed by the xylem. This reduces hydrostatic pressure at the bottom of the phloem.
• How is ringing used as evidence for mass flow?

  -bark containing phloem is removed from the tree

  -xylem is left intact

  -fluid accumulates in the phloem on the source side of the tree, causing swelling

  -tissues below the removed ring of bark will die as they cannot get organic materials
• How are aphids used as evidence for mass flow?

  -aphids feed by inserting their mouthpiece directly into the phloem

  -body of aphid is removed, sap leaks out of the mouthpiece

  -this shows phloem is under positive pressure and transports organic materials