(N/A) $\Rightarrow$ Source: The part of the plant where food is synthesized,typically the leaves.
$\Rightarrow$ Sink: The part of the plant where food is stored or utilized,such as roots,stems,or developing buds.
$\Rightarrow$ Food,primarily in the form of sucrose,is transported by the vascular tissue phloem from a source to a sink.
$\Rightarrow$ The source-sink relationship is not fixed; it can be reversed depending on the season or the plant's physiological needs.
$\Rightarrow$ For example,sugar stored in roots may be mobilized to become a source of food in early spring to support the growth of developing buds.
$\Rightarrow$ Unlike xylem transport,which is unidirectional,phloem transport is bidirectional.
$\Rightarrow$ Bidirectional movement means that food in the phloem sap can be transported in any required direction,provided there is a source of sugar and a sink capable of using,storing,or removing it.
$\Rightarrow$ Phloem sap consists mainly of water and sucrose,but it also transports other sugars,hormones,and amino acids.