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Transport in Plants

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12

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

The leaves carry out photosynthesis and act as the source of the food. The phloem conducts the food from the source to the sink (the part of the plant requiring or storing food).  But, the source and sink may be reversed depending on the season, or the plant’s needs.  During spring, the food stored in the sink is mobilised 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) as the realtion of source and sink is variable.

However, 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.


Give the term for the ability to resist a pulling force.

Tensile strength

Why the cortex produces no resistance to movement of water ?

The cortical cells are loosely packed and produce no resistance to movement of water via cell walls or apoplast.

Why the water is forced to move through cell membrane beyond endodermis ?

Water is forced to move through cell membranes beyond endodermis because of the suberin (waxy substance) present on radial walls of endodermal cells blocks water and solute movement through cell walls of endodermis. 

Who introduced the apoplast—symplast concept ?

E. Munch (1930).

What is transmembrane pathway ?

The movement of water through cell membranes is called trans membrane pathway.