Describe the way solutes are transported in a plant's vascular system

Solutes (e.g sucrose) are transported in the phloem from source to sink. Sucrose is made at the leaves in the plant, this is actively transported into the phloem via companion cells. This then lowers the water potential of the phloem, so water moves in from the xylem via osmosis. As a result, the hydro-static pressure of the phloem is increased so the solutes in the phloem move down their hydro-static pressure gradient. This means they move down from the source to the sink which is in the roots. This is where sucrose is removed via companion cells and stored, then water moves out of the phloem via osmosis, which lowers the hydro-static pressure in this area of the phloem and so this process maintains a pressure gradient allowing solutes to continue to move from source to sink.