Phloem
Transport
The food synthesised by
the leaves are transported by the phloem either to the area of requirement or
stored. Phloem tissue is composed of sieve tubes which have sieve plates.
Cytoplasmic strands pass through the pores in the sieve plates.
Phloem transports food
(sucrose) from a source to a sink. The source is part of the plant that
synthesize food, i.e., the leaf, and sink, is the part that needs or stores the
food. But, the source and sink may be reversed depending on the season, or the
plant’s need.
Since the source-sink
relationship is variable, the direction of movement in the phloem can be
upwards or downwards, i.e., bidirectional. In contrast, the movement is
always unidirectional in xylem i.e., upwards.
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