Question

Question 14 Explain why xylem transport is unidirectional and phloem transport bi-directional.

Class XI Biology Chapter - Transport in Plants Page 193

Answer 1

Xylem flow is unidirectional and phloem flow is bidirectional because xylem transport water from soil to leaves and phloem transfers the food synthesized in leaves to all the parts of plants wherever it is necessary.

Answer 2

During the growth of a plant, its leaves act as the source of food as they carry out photosynthesis. The phloem conducts the food from the source to the sink (the part of the plant requiring or storing food). During spring, this process is reversed as the food stored in the sink is mobilized toward the growing buds of the plant, through the phloem.

Thus, the movement of food in the phloem is bidirectional (i.e., upward and downward).

The transport of water in the xylem takes place only from the roots to the leaves.

Therefore, the movement of water and nutrients in the xylem is unidirectional.

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