Question

In a plant, translocation in xylem is unidirectional while in phloem it is bidirectional. Explain.

Answer 1

Translocation in xylem is uni-directional:

Translocation of water and minerals in xylem depends on the transpirational pull and root pressure. Therefore, it is unidirectional due to transpiration pull being developed from roots to leaves.


Translocation in phloem is bi-directional:

• Translocation of food in phloem depends on the source and sink relationship. Source is the part of the plant which synthesises the food example leaves and sink is the part that needs or stores the food (example roots)
• The source-sink relationship is variable depending on the season, or requirements of the plant. So the direction of movement can be upwards or downwards in the phloem. Therefore the translocation food in phloem is bi-directional. ​​​​​​