What does phloem primarily transport within the tree?

Phloem is primarily responsible for the transport of soluble organic compounds, mainly sugars produced through photosynthesis. These compounds are crucial for providing energy and building materials for the tree, moving from the leaves where they are synthesized to other parts of the tree, such as roots and developing fruits. This transport process is essential for the maintenance of the tree's growth and energy balance, as these organic compounds are also used for cellular respiration and other metabolic activities.

The other options involve substances that are transported by different systems or parts of the tree. Water and minerals are primarily absorbed by the roots and transported through the xylem. Oxygen and carbon dioxide are gases exchanged through the stomata of leaves and are not specifically transported by phloem. Waste products may be handled in various ways by the tree but are not the primary function of phloem. Therefore, the role of phloem in transporting soluble organic compounds is critical to the tree's overall functionality and health.