Q 12. “Movement in xylem is unidirectional, while in phloem movement is from source to sink.” Elaborate.
Dear student.
Upward movement of water and minerals in the xylem depends on transpiration. Therefore it is always unidirectional. The phloem transport depends on the source-sink relationship. Therefore, the movement of phloem sap is bi-directional.
Foods are synthesised in the plants with photosynthesis which occurs in the leaves of the plant, so the leaves are the source. The synthesised food is translocated to other parts of the plant for their use and storage(sink). At the time of emergence of new buds, the direction gets reversed and stored food are translocated from sink to growing buds of the plant. So, the movement through phloem in bi-directional.
But in case of xylem, the transport of water takes place only from the roots to the leaves through xylem, most of the water is lost in transpiration, so the demand of water is again renewed from root to leaves, this is because transport in xylem is unidirectional.
Regards.
Upward movement of water and minerals in the xylem depends on transpiration. Therefore it is always unidirectional. The phloem transport depends on the source-sink relationship. Therefore, the movement of phloem sap is bi-directional.
Foods are synthesised in the plants with photosynthesis which occurs in the leaves of the plant, so the leaves are the source. The synthesised food is translocated to other parts of the plant for their use and storage(sink). At the time of emergence of new buds, the direction gets reversed and stored food are translocated from sink to growing buds of the plant. So, the movement through phloem in bi-directional.
But in case of xylem, the transport of water takes place only from the roots to the leaves through xylem, most of the water is lost in transpiration, so the demand of water is again renewed from root to leaves, this is because transport in xylem is unidirectional.
Regards.
