Transport systems in plants: phloem and translocation

Sugars, amino acids and other organic substances (nutrients) are transported in phloem. Translocation starts at a source, such as a leaf where sugars are made. Sugars are transported into phloem by active transport across the membranes of the living phloem cells. Water moves into the phloem cells by osmosis, which increases the pressure and pushes the sugars along the phloem tube. Sugars are transported out of the phloem by active transport at a sink, such as a developing root, stem or flower.