Class 11 Biology Transport In Plants Phloem transport: flow from source to sink

Phloem transport: flow from source to sink

  • Sucrose is transported by the vascular tissue phloem from a source to a sink.
  • Source is the place which synthesises the food, i.e., the leaf and sink is the part that needs or stores the food.
  • Since the source-sink relationship is variable, the direction of movement in the phloem can be upwards or downwards, i.e., bi-directional, which contrasts with that of the xylem where the movement is always unidirectional, i.e. upwards.
  • Food in phloem sap can be transported in any required direction.
  • Phloem sap transports water and sucrose, but other sugars, hormones and amino acids are also transported or translocated through phloem.


Fig. Source-sink relationship

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