Phloem

• What does the phloem do?

  Transports sugars through the plant
• What is translocation?

  The transport of sugars from source to sink. Requires ATP
• What is the liquid that is being transported in the phloem?

  Phloem sap
• What is the source (where the sugars come from)?

  Leaves or storage organs
• What is the sink (where the sugars go)?

  Meristems or roots
• What is the mass flow theory?

  Explains how sugars are transported through the phloem
• What is the process of translocation in the source?

  • Source cells produce sucrose
  • Sucrose is actively transported from source into sieve tubes via companion cells, lowering water potential
  • Water moves in from xylem to sieve tube, increasing pressure
• What is the process of translocation at the sink?

  • Sucrose moves out of sieve tubes into sink cells by active transport
  • This decreases water potential in the sink
  • Volume and hydrostatic pressure in sieve tubes decreases, making a pressure gradient between source and sink
  • This causes mass flow of sucrose from source to sink